can be adequately opened from a lateral to medial direction starting in its middle portion, even though proximal control is not achieved. In such cases, if the aneurysm will be exposed partially during opening of the sylvian fissure, the surgeon should move further proximally to obtain control of the proximal M1 segment. In the standard transsylvian approach, it is important to remember that the aneurysm usually is located more superficially. Regardless of the length of M1, if the M1 can curve downward toward the skull base, it is easier to just expose the M1 segment to the aneurysm by distal transsylvian approach. In these cases, if we select the conventional transsylvian approach, we may seize the aneurysm before internal carotid artery. So we need not see the internal carotid artery. In the case of long M1 segment, the aneurysm is usually within the temporal lobe. We can catch the proximal M1 by dissection of frontal side of a sylvian fissure.

Distal MCA aneurysms can be approached through an opening of the lateral sylvian fissure. The surgeon usually begins such opening in the middle portion of the fissure and proceeds distally. It is easy to mistake one of the deeper sulci for the sylvian fissure distally. To confirm that the sylvian fissure is actually being entered, the surgeon should trace one of the branches of the MCA proximally. The opening of the distal sylvian fissure must be done meticulously to avoid damaging adjacent areas of the brain, which have great functional importance. If severe intratemporal hemorrhage or brain swelling makes the opening of the fissure impossible, the surgeon can make an incision through the middle temporal gyrus and perfonn brain resection with a suction until the sylvian fissure is exposed.

In case 2 (Fig. 15.6), we operated by distal approach for usual MCA aneurysm.

**Fig. 15.6** Case 2. Ruptured MCA aneurysm with long and curved downward toward skull base M1, 36-year-old male. (**a**) CT scan revealed SAH with Fisher group 3. (**b**) CTA on admission showed ruptured MCA aneurysm (arrow). M1 segment curve downward toward the skull base. (**c**) Postoperative DSA showed disappearance of aneurysm. (**d**) Simulation image by preoperative CTA

showed anatomical relationship of M1, M2, aneurysm, sylvian vein, and skull bone. You can understand the relationship of aneurysm and M1–M2 junction in operative field. (**e**) Dissection of aneurysmal neck by microdissector. (**f**) After appliance of the temporary clip to proximal M1, neck clipping by mini clip is applied

#### **15.4.9 Dissection of the Aneurysm and Neck Clipping**

After the proximal and distal vessels have been exposed, dissection of the aneurysm can begin. During this stage of the operation, we usually employ temporary clipping of the proximal vessel, with keeping normotension over 100 mmHg of systolic blood pressure, normothermia under 36.5 °C, and brain protective drugs. The aneurysm must be dissected in its neck, with no perforating vessels remaining adherent to the posterior surface of the aneurysm. It is sometimes useful to place a tentative clip across the dome of the aneurysm and then to dissect it from around the structure further before placing the final clip. MCA aneurysms often have a wide-based neck that involves 180° or more of the circumference of the bifurcation point. Optimal occlusion of such aneurysms requires the use of the application of multiple clips (Fig. 15.7). In some of these cases, it may also be necessary to use wrapping with some material to reinforce any unclipped areas of the neck. Perforators arising from the MCA must be handled with care. Most lenticulostriate vessels arise from the posteromedial surface of the M1 segment and enter the anterior perforated substance to supply the internal capsule and the basal ganglia.

Often, pan of the neck or dome is adherent to the vein and small artery. A fine micro dissector and microscissors are useful in the dissection from their vessels (Figs. 15.8 and 15.9). After the neck has been identified, selection and appliance of optimal clip help protect these vessels. Usually, multiple clips are needed for proper clipping of the MCA aneurysm.

#### **15.4.10 Dural Closure**

Primary tight dural closure by nylon suture with fibrin glue can prevent liquorrhea postoperatively.

#### **15.5 Surgeon Plan to Handle the Complication**

Many MCA aneurysms have a wide-based neck. Accordingly, placement of the clip may compromise the origin of one of these vessels, especially if the base of the aneurysm is partially calcified or atherosclerosis. A lenticulostriate artery originates from the deep side of the MCA distally along the M1 segment close to the bifurcation. This vessel may be occluded inadvertently by the tips of the aneurysm clip.

**Fig. 15.7** Multiple clipping method for broad neck MCA aneurysm. (**a**) Broad neck MCA aneurysm. (**b**) Multiple clipping methods for MCA aneurysm using ring clip

**Fig. 15.8** Dissection between vein and aneurysm. (**a**) Dissection between vein and aneurysm by micro dissector. (**b**) Dissection between vein and aneurysm by microscissors

**Fig. 15.9** Dissection between small artery and aneurysm. (**a**, **c**) Dissection between small artery and aneurysm by micro dissector. (**b**) Dissection between vein and aneurysm by microscissors

Thus, after the aneurysm clip is placed, it is important to visually inspect the tips of the aneurysm clip and to auscultate the M1 branches with a micro-Doppler probe. To inspect the all arteries around aneurysm, we must check them by using indocyanine green (ICG) video angiography. There are rare cases of postoperative small infarction of perforating area in spite of checking these modalities completely. So, MEP is the most useful intraoperative monitoring especially in M1 aneurysm in relation with lenticulostriate artery. If the wave of MEP reduced in its amplitude under 50% after neck clipping, we should release the clip and investigate all around aneurysm and find the obstructed lenticulostriate artery. MEP is very sensitive regarding with the damage of corticospinal tract, so we can trust MEP monitoring. If the patient has postoperative small infarction by MRI, he (she) is asymptomatic as long as MEP is normal.

It is important to reduce the pressure of parent artery and aneurysm using temporary arterial occlusion during the neck clipping of broadbased MCA aneurysm. In all cases, the brain must be protected during temporary arterial occlusion by brain protected drug, avoiding not only hyperthermia but also hypotension. The temporary occlusion time is usually less than 5 min per once. At the conclusion of the clipping process, papaverine is applied over the vessels to relax the mechanical spasm.

Preoperative three-dimensional CTA can enhance the surgeon's ability to picture the anatomy of the aneurysm before surgery to plan the optimal clipping.

#### **15.6 Expert Opinion/Suggestion to Avoid Complication**

In patients with giant MCA aneurysms, the surgeon must often completely trap the MCA and its branches and empty the aneurysm before final clipping. However, even with this technique, it is impossible to achieve optimal clipping of some heavily thrombosed or calcified aneurysms. Such cases often require a bypass procedure. Options include the STA to MCA bypass, the saphenous vein graft, and radial artery graft bypass to the major branches of MCA, transposition of some MCA branches.

Large sylvian veins should be left intact and displaced laterally with the temporal lobe or medially with frontal lobe. We can preserve almost all sylvian vein by careful finding the anastomosis between sylvian veins. Extremely small bridging veins across the sylvian fissure call can be safely cauterized and divided; however, we should understand that careful dissection of small veins can lead us expert microsurgeon.

#### **15.7 Things to Be Observed and Postoperative Care/ Follow-Up**

In case of SAH, the prevention and treatment of delayed cerebral ischemia (DCI) are essential. We use intraoperative irrigation by artificial cerebrospinal fluid (CSF) (Artcereb) and postoperatively statin, cilostazol for prevention of DCI. Especially in severe cases of MCA aneurysm with sylvian hematoma, external decompressive craniotomy is performed for better circulation of CSF to prevent the DCI.

#### **References**

**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

## **Surgery of Posterior Cerebral Artery Aneurysm**

**16**

Joseph C. Serrone, Ryan D. Tackla, and Mario Zuccarello

#### **16.1 Sign and Symptoms**

This case illustration was a 62-year-old male presenting with the acute onset of worst headache of life symptoms (Hunt and Hess grade 2). Head computed tomography (CT) revealed Fisher grade 3 subarachnoid hemorrhage (SAH).

#### **16.2 Investigation**

As in most centers, CT angiography is the preferred imaging modality for the identification and evaluation of intracranial aneurysms at our institution. In this case, the CT angiogram revealed a 3.5-mm saccular aneurysm arising from P1 segment of right posterior cerebral artery (PCA) (Figs. 16.1 and 16.2).

#### **16.3 Preoperative Preparation**

Procurement of proximal control must be considered first when preparing to approach any ruptured aneurysm. For PCA aneurysms, we obtain proximal control at the distal part of basilar artery

Department of Neurosurgery, Virginia Mason Medical Center, Seattle, WA, USA

© The Author(s) 2019 135 J. July, E. J. Wahjoepramono (eds.), *Neurovascular Surgery*, https://doi.org/10.1007/978-981-10-8950-3\_16

**Fig. 16.1** A superiorly projecting right P1 segment PCA aneurysm is seen from this CT angiogram. Also of note, the basilar apex is well above the posterior clinoidal process allowing easy exposure of the basilar artery from an anterolateral approach for proximal control

**Fig. 16.2** Using CT angiography to create a surgical view of the aneurysm, neurosurgeons can study the vascular anatomy as it will be encountered intraoperatively. This view, through the supracarotid window, exposes the aneurysm well for clip application

J. C. Serrone · R. D. Tackla

M. Zuccarello (\*) Department of Neurosurgery, University of Cincinnati, Cincinnati, OH, USA e-mail<EMAIL_ADDRESS>
just proximal to the origins of the superior cerebellar arteries. This area of the basilar artery is usually devoid of brainstem perforating arteries. The anatomical obstruction when approaching the posterior circulation through a pterional craniotomy is the posterior clinoid process (PCP). The relationship of the PCP to the basilar apex is assessed through sagittal or coronal reconstruction of the CT angiogram, which best demonstrates vascular and bone anatomy. If the basilar apex is above the PCP, it is possible to obtain proximal control of the basilar artery prior to clipping the posterior cerebral artery aneurysm. If the basilar apex is at the level of the PCP, removal of the PCP with a drill or ultrasonic bone curette may be required to achieve proximal control. If the basilar apex is below the PCP, proximal control cannot be achieved with a pterional approach, and a subtemporal approach is usually preferred.

#### **16.3.1 Approach**

Dealing with most aneurysm near basilar apex (including P1 segment aneurysms), we prefer an anterolateral approach based upon the pterional approach popularized by Dr. Yasargil [1]. As an extension of this approach, the pterional approach via the extended lateral (PAVEL) corridor is helpful [2]. The patient position is supine, with the head extended and rotated 15° contralaterally (Fig. 16.3). Relevant anatomy to consider when planning the craniotomy includes the superficial temporal artery, frontalis branch of facial nerve, and frontal sinus (Fig. 16.4) [3]. A branch of superficial temporal artery is often encountered during the skin incision and must be ligated. The skin incision must remain posterior to the frontalis branch of the facial nerve for prevention of postoperative frontalis palsy. The extent of pneumatization of the frontal sinus should be assessed preoperatively to prevent encountering the frontal sinus during craniotomy. In the event that the craniotomy is exposing the frontal sinus, cranialization of frontal sinus should ensue.

After minimal shaving of the hair, a skin incision is made behind the hairline. The incision

**Fig. 16.3** The patient is positioned supine with the head extended and rotated 15° contralaterally. Relevant anatomy when using the pterional approach is seen with this schematic. Commonly the frontal branch of the superficial temporal artery is under the skin incision and must be ligated. The skin incision is kept posterior to the frontalis branch of the facial nerve to prevent its injury. There is wide variation in the pneumatization of the frontal sinus, and this must be studied preoperatively to prevent entering the sinus and causing a cerebrospinal fluid leak (Printed with permission from Mayfield Clinic)

**Fig. 16.4** The skin incision has been made with the myocutaneous flap retracted anteriorly. A frontal, temporal, and posterior burr hole is made to aid in dissection of the dura from the inner skull cortex and prevents a durotomy by the craniotome (Printed with permission from Mayfield Clinic)

starts 1 cm anterior to tragus at zygoma root, and curve extends to midline. Then myocutaneous flap is detached in one single layer and retracted with spring hooks toward the anterior to expose the orbital rim. We prefer a one layer myocutaneous flap as opposed to an inter- or subfascial dissection that is associated with more jaw pain and temporal wasting [4]. Three burr holes are made to allow adequate dissection of the dura

**Fig. 16.5** Using a craniotome, cuts 1–3 are made until the sphenoid ridge is encountered. Cut #4 is made with a high-speed drill. Green-shaded area represents the thickened bone of the sphenoid ridge, which will subsequently be drilled off (Printed with permission from Mayfield Clinic)

away from the inner skull cortex (Fig. 16.5). A side-cutting craniotome with footplate is used to create a bone flap from the supraorbital notch, medially, to the mid-temporal lobe, exposing Sylvian fissure laterally. Sphenoid ridge is then drilled off in its entirety with the coarse diamond drill. Dura is cut with curvilinear shape and reflected anterolaterally.

#### **16.4 Steps of the Surgery**

When clipping posterior circulation aneurysms through the pterional approach, the neurosurgeon works through the opticocarotid, oculocarotid, and supracarotid windows (Figs. 16.6 and 16.7). To safely access these corridors, mobilization of the temporal lobe is required [2]. This is accomplished with several key steps. It is important to split the sylvian fissure widely, and expose the supraclinoidal ICA (internal carotid artery) and MCA (middle cerebral artery). This is a crucial step, as retracting the temporal lobe without detethering the ICA and MCA can result in a vascular injury and stroke [5]. The middle Sylvian vein at its entrance into the sphenoparietal sinus must be coagulated and cut to allow for retraction of the anterior temporal lobe. Subsequent dissection is done to mobilize the anterior choroidal artery from the uncus, making it possible to retract the tempo-

**Fig. 16.6** After opening of the proximal Sylvian fissure, wide exposure of the optic nerve (CN2), supraclinoidal internal carotid artery (ICA), and oculomotor nerve (CN3) are demonstrated. The opticocarotid and oculocarotid windows are visualized

**Fig. 16.7** Further dissection allows utilization of the supracarotid window above the carotid terminus, which will eventually be used for clipping of the PCA aneurysm. Exposure of the basilar artery within the opticocarotid window is well seen from this image. The opticocarotid window will be used for temporary clipping of the basilar artery for proximal control

ral lobe laterally. Lastly, third cranial nerve is followed posteriorly, and Liliequist membrane is opened to get to PCA (posterior cerebral artery). These steps comprise the PAVEL extension of the pterional approach and are described in detail elsewhere [2].

After extensive subarachnoid dissection in this case, the opticocarotid corridor was used to obtain proximal control at basilar artery (Fig. 16.8). With the proximal control achieved, attention was directed toward the P1 segment aneurysm through the supracarotid window (Fig. 16.9). Given that this was a simple, small aneurysm, a straight clip was used to occlude the

**Fig. 16.8** A temporary clip is being placed on the basilar artery through the opticocarotid window

**Fig. 16.9** The temporary clip has been placed on the basilar artery through the opticocarotid window. Looking above the carotid terminus (through the supracarotid window), the aneurysm is well exposed for clipping

aneurysm (Fig. 16.10). Lastly, the tips of the clip were inspected through the opticocarotid window to ensure the aneurysm was completely occluded and that no thalamoperforator arteries were incorporated within the clip (Fig. 16.11).

#### **16.5 Surgeon Plans to Handle the Complication**

A dreaded complication when using the pterional approach for posterior circulation aneurysms is vascular dissection of the middle cerebral artery [5]. Management of this complication depends on the presence of collaterals and the time from ictus. If the complication is identified intraoperatively by loss of somatosensory-evoked potentials or motor-evoked potentials, surgical revascular-

**Fig. 16.10** A temporary clip has been placed on the basilar artery through the opticocarotid window. The PCA aneurysm is being clipped through the supracarotid window with a straight aneurysm clip

**Fig. 16.11** After permanent clip placement through the supracarotid window and removal of the temporary clip, the tips of the permanent clip are inspected through the opticocarotid window to ensure complete occlusion of the aneurysm without incorporation of thalamoperforator arteries within the clip blades

ization by middle cerebral artery thrombectomy or bypass between the external carotid artery and the middle cerebral artery should be considered. However, the dissection commonly occurs during surgery, but occlusion of MCA occurs in a delayed fashion, with the acute onset of hemiparesis occurring postoperatively. At this time, cerebral angiography should be performed.

With good collaterals, postoperative augmentation of blood pressure is the preferred treatment. If poor collaterals are seen and the ictus of the patient's stroke is within 6 h, endovascular or surgical revascularization can be considered. Endovascular therapy is approached with caution, as the patient will require some form of anticoagulation or antiplatelet therapy after thrombectomy to prevent recurrent occlusion. If there is any uncertainty regarding the timing of ictus, revascularization should be avoided, as this will likely result in the conversion of a morbid ischemic complication into a fatal hemorrhagic complication. The size of the stroke should be assessed radiographically for consideration of a prophylactic decompressive hemicraniectomy in order to prevent cerebral herniation due to malignant middle cerebral artery infarction.

#### **16.6 Expert Opinion/Suggestion to Avoid Complication**

Like most complications, they are better to prevent than manage. This complication is prevented by extensive mobilization of the temporal lobe and detethering of the middle cerebral artery as described above. In fact, the PAVEL extension of the pterional approach was developed specifically to prevent the complication of the middle cerebral artery injury while approaching basilar aneurysms [2, 5].

#### **16.7 Things to Be Observed and Postoperative Care/ Follow-Up**

This is a ruptured cerebral aneurysm case that will have the clinical sequelae of SAH, including posthemorrhagic cerebral vasospasm. Prophylactic treatment of vasospasm should include maintenance of a euvolemic state and administration oral nimodipine. Monitoring of posthemorrhagic cerebral vasospasm with frequent neurological exams and transcranial Doppler ultrasound should be performed. Consideration of cerebral angiography with endovascular treatment of vasospasm should occur with alterations of the neurological exam or elevation in transcranial Doppler ultrasound velocities. In accordance with recently published guidelines, delayed cerebrovascular imaging is recommended after clipping of ruptured aneurysms to evaluate for aneurysm recurrence (which occurs in approximately 4%) [6].

#### **References**

**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

**17**

## **Surgery of Upper Basilar Artery Aneurysm**

Kentaro Mori, Terushige Toyooka, and Naoki Otani

#### **17.1 Signs and Symptoms**

Aneurysms of the basilar artery (BA) may occur at several locations including the BA-vertebral artery junction, BA-anterior inferior cerebellar artery junction, BA-superior cerebellar artery junction, and BA tip. Upper BA aneurysm is usually considered to include BA tip aneurysm and BA-superior cerebellar artery junction aneurysm. BA aneurysm seldom manifests as neurological problems before rupture. Partially thrombosed BA aneurysm may manifest as progressive neurological deficits due to compression of the brain stem and cranial nerves caused by aneurysm growth. Unruptured BA tip aneurysm has a higher tendency to rupture compared to other types of cerebral aneurysm. Therefore, the surgical indications for unruptured BA aneurysm should consider this fact as well as the age, size, and shape of the aneurysm.

#### **17.2 Investigation**

Upper BA aneurysms are surrounded by many important osseous and neurovascular structures such as the anterior (ACP) and posterior

K. Mori (\*) · T. Toyooka · N. Otani

clinoid processes (PCP), optic nerve, oculomotor nerve, internal carotid artery (ICA), posterior communicating artery and its perforators (anterior thalamoperforating arteries), and posterior cerebral artery and its perforators (posterior thalamoperforating arteries: PTPAs) (Fig. 17.1). The PTPAs arise from the superior or posterosuperior surface of the P1 segment of the posterior cerebral artery and at a distance of 0.41–4.71 mm (mean 1.93 mm) from the BA apex. The PTPAs number 1–8 (mean 3.6) with diameter of 0.24–1.18 mm (mean 0.7 mm) [1]. Dissection of the PTPAs from the BA tip aneurysm is the key step to successful clipping surgery.

#### **17.3 Preoperative Preparation**

Three-dimensional computed tomography angiography and/or digital subtraction angiography are mandatory to investigate the BA complex with the aneurysm (Fig. 17.2). The distance of the aneurysm neck from the clinoid line (the line between the tips of the ACP and PCP) is particularly important to determine the operative approach. Anterolateral approaches such as the pterional transsylvian approach and extradural temporopolar approach (ETA) are suitable for the treatment of BA aneurysms located between 15 mm above and 5 mm below the clinoid line. The subtemporal transtentorial approach or

Department of Neurosurgery, National Defense Medical College, Tokorozawa, Saitama, Japan e-mail<EMAIL_ADDRESS><EMAIL_ADDRESS><EMAIL_ADDRESS>
<sup>©</sup> The Author(s) 2019 141 J. July, E. J. Wahjoepramono (eds.), *Neurovascular Surgery*, https://doi.org/10.1007/978-981-10-8950-3\_17

**Fig. 17.1** Illustration of the basilar artery (BA) complex with BA tip aneurysm via the anterolateral approach. Note the anterior thalamoperforating arteries from the posterior communicating artery (p-com) and the posterior thalamoperforating arteries from the posterior cerebral artery (P1 and P2). *II* optic nerve, *III* oculomotor nerve, *IV* trochlear nerve, *V* first branch of trigeminal nerve, *ACP* anterior clinoid process(resected), *PCP* posterior clinoid process, *IC* internal carotid artery, *SCA* superior cerebellar artery

anterior petrosal approach should be considered for aneurysms located more than 5 mm below the clinoid line.

#### **17.3.1 Approach**

#### **<IP_ADDRESS> Extradural Temporopolar Approach ETA**

The pterional transsylvian approach and subtemporal transtentorial approach are usually used to treat upper BA aneurysms, but both have advantages and disadvantages. The anterior temporal approach, which retracts the temporal tip posteriorly, combines the advantages of both these approaches and facilitates the surgical trajectory from the anterolateral direction. The anterior temporal approach is a pure intradural approach based on dissecting the superficial middle vein and anterior temporal artery from the temporal lobe. The ETA is an epidural approach involving posterior displacement of the temporal lobe with

**Fig. 17.2** Three-dimensional computed tomography angiograms of a case of basilar tip aneurysm. *Left* preoperative, *Right* postoperative

the dura mater [2, 3] and includes extradural anterior clinoidectomy, optic canal opening, peeling the lateral wall of the cavernous sinus, and retraction of the temporal lobe over the dura mater. The ETA enables the neurosurgeon to pass through the open anterior part of the cavernous sinus to the retrocarotid space and interpeduncular cistern. Such epidural temporal lobe retraction is less likely to cause contusion. Furthermore, opening the oculomotor foramen and drilling the PCP provide space for securing the proximal BA. The use of the ETA for treatment of BA top aneurysm is discussed below.

#### **<IP_ADDRESS> Patient Position, Skin Incision, and Craniotomy**

After induction of general anesthesia, lumbar spinal drainage is placed for cerebrospinal fluid (CSF) aspiration to relax the dural tension during the epidural procedures. The patient is placed in the supine position, and the head is rotated away from the operative side at about 30° (Fig. 17.3). Semi-coronal skin incision and interfascial dissection of the temporal muscle fascia are then performed. The temporal muscle is detached from the superior temporal line but not incised. The temporal muscle is dissected subperiosteally

**Fig. 17.3** Scheduled skin incision, frontotemporal craniotomy with orbitozygomatic osteotomy

**Fig. 17.4** After frontotemporal craniotomy with orbitozygomatic osteotomy. *ZA* zygomatic arch, *OR* orbit (opened), *FD* frontal dura mater, *TD* temporal dura mater

and retracted posteroinferiorly using fish hooks. Standard frontotemporal craniotomy is performed with the anterior border at the midpoint of the orbit, and the temporal squama is rongeured out until the floor of the middle cranial fossa is exposed. If the orbitozygomatic approach is needed for specific cases such as high position BA tip aneurysm, the orbitozygomatic bar is removed as in the two-piece method (Fig. 17.4).

#### **17.4 Steps of the Surgery**

The frontal dura and the temporal dura are dissected subperiosteally until flush with the frontal and middle fossae. The lesser wing of the sphenoid and the orbital apex is drilled away until the meningo-orbital band is exposed. Dissection of the middle fossa dura is continued until the orifices of the superior orbital fissure (SOF) and foramen rotundum are exposed (Fig. 17.5). The roof of the SOF is opened to a width of 2 mm to expose the junction between the dura propria of the temporal lobe and the periosteal dura (Fig. 17.5 arrowhead). The meningo-orbital band is pulled proximally using forceps or a

**Fig. 17.5** Junction between the dura propria of the temporal dura mater (TD) and periosteum at the superior orbital fissure (SOF). *FD* frontal dura mater, *MOB* meningo-orbital band, *OR* orbit. Arrowhead indicates the junction

**Fig. 17.7** After peeling of the dura propria (DP) of the temporal dura mater and exposure epidurally of the anterior clinoid process (ACP). *V1* ophthalmic branch of the trigeminal nerve, *V2* maxillary branch of the trigeminal nerve. Open triangle shows Mullan's anterolateral triangle

**Fig. 17.6** Cutting the meningo-orbital band (MOB)

stitch and cut with micro-scissors for about 4 mm. The tip of the micro-scissors should be pointed toward the exposed junction at the SOF (Fig. 17.6). Any bleeding from the meningoorbital artery should be coagulated and divided. Peeling of the dura propria from the inner membrane can be started anywhere, with the easiest point between the SOF and foramen rotundum, using a micro-dissector with a sharp edge. If the dura propria and inner membrane are tightly attached, sharp dissection using micro-scissors is recommended. The peeling is continued until the entire ACP is exposed epidurally. The trochlear nerve and first and second branches of the trigeminal nerve can be seen though the semitransparent inner membrane (Fig. 17.7). Care should be taken to maintain the sphenoparietal sinus at the dura propria side and to stop the peeling at the point where the sphenoparietal sinus drains into the cavernous sinus to prevent problems with venous congestion. Drilling of the ACP with a high-speed drill using saline irriga-

**Fig. 17.8** Completion of epidural procedures after removal of the anterior clinoid process and opening of the optic canal. *II* optic nerve, *III* oculomotor nerve, *V1* ophthalmic branch of the trigeminal nerve, *V2* maxillary branch of the trigeminal nerve, *C3* clinoid segment of the internal carotid artery, *DP* dura propria. Open triangle shows Dolenc's anteromedial triangle

tion is started from the lateral part of the ACP, and the optic canal is then opened partially in the medial part of the ACP. The ACP is hollowed like an egg shell, and the remainder of the ACP can be removed en bloc. The anterior loop of the ICA (clinoid segment, C3) in the opened clinoid space can be seen through the thin carotid oculomotor membrane. The partially opened optic canal can be enlarged using a micro-punch, and the remainder of the optic strut between the opened clinoid space and optic canal can be removed with either a small diamond drill or a micro-punch (Fig. 17.8). During the skull base drilling, if the posterior ethmoid sinus is opened and the mucous membrane is injured, a muscle piece should be inserted and sealed with fibrin glue to avoid CSF leakage. At this point, the temporal lobe with the temporal dura mater can be displaced posteriorly by 25–30 mm from the tip of the middle cranial fossa. The dura mater is cut along the sylvian fissure as far as the optic nerve, the falciform ligament is cut, and then the dural cutting is continued to the inferior frontal dura mater in an L-shaped fashion over the distal dural ring. Incision of the falciform ligament and distal dural ring will facilitate movement of the optic nerve and ICA. Before tentorial incision, the sylvian fissure should be opened widely, and the arachnoid membrane around the oculomotor nerve should be incised to free the nerve from the medial temporal lobe. By observing at the cisternal and extradural parts of the oculomotor nerve, the medial tentorial edge is cut for separation from the cavernous sinus around the oculomotor nerve. Following these procedures, the temporal lobe can be retracted posteriorly with the temporal dura mater to complete the ETA with the surgical corridor of the opened anterior part of the middle fossa and the cavernous sinus (Fig. 17.9). Opening of the oculomotor foramen facilitates mobilization of the oculomotor nerve. If the target pathology is located beneath the PCP, the latter can be drilled away to expose the pontine cistern to secure the proximal BA. The ICA is retracted medially to expose the BA complex with the BA tip aneurysm (Figs. 17.10 and 17.11). After temporary clips are applied to the

**Fig. 17.9** After dural opening and tentorial incision. The falciform ligament (FL) and the distal dural ring (DDR) are incised. The tentorium is incised along the anterior petroclinoid ligament (APCL). The temporal dura is retracted posteriorly with the temporal dura mater (TD). *II* optic nerve, *III-I* intradural oculomotor nerve, *III-E* extradural oculomotor nerve, *IV* trochlear nerve, *V1* ophthalmic branch of the trigeminal nerve, *V2* maxillary branch of the trigeminal nerve, *C3* clinoid segment of the internal carotid artery

**Fig. 17.10** Basilar artery (BA) complex and BA tip aneurysm. Note the small thalamoperforating arteries around the aneurysm (AN). *IC* internal carotid artery, *A1* anterior cerebral artery, *M1* middle cerebral artery, *R-PCA* right posterior cerebral artery, *L-PCA* left posterior cerebral artery

**Fig. 17.11** Dissection of the basilar tip aneurysm (AN) via the retrocarotid space. *p-com* posterior communicating artery, *IC* internal carotid artery

**Fig. 17.12** After neck clipping of the basilar tip aneurysm

BA and bilateral posterior cerebral arteries, aneurysm dissection is started. If the posterior communicating artery obstructs the operative view, this vessel can be ligated and divided except for the fetal type. Great care is required to dissect the PTPAs in the vicinity of the aneurysm before neck clipping is performed (Fig. 17.12). After clipping of the aneurysm, the dural defect around the dural ring can be approximated with a small piece of harvested temporal fascia and fibrin glue. The skull is fixed with titanium plates, a subcutaneous drain is placed, and the wound is closed as usual.

#### **17.5 Specific Plans to Handle Complications and Expert Opinion**

#### **17.5.1 How to Avoid Heat Injury During Skull Base Drilling**

Constant cooling with saline irrigation is extremely important to avoid heat injury to the neurovascular structures. Before drilling the ACP, the ACP should be carefully dissected from the surrounding tissue because the oculomotor nerve passes along the inferolateral face of the ACP. The optic canal is partially opened with a drill and should be enlarged using a micro-punch. Opening the optic canal using a micro-punch can avoid heat injury.

#### **17.5.2 How to Control Bleeding from the Cavernous Sinus**

There are two major points of bleeding from the cavernous sinus, Dolenc's anteromedial triangle and Mullan's anterolateral triangle. Bleeding from the cavernous sinus can be controlled by packing with Surgicel® cotton soaked with fibrin glue or direct injection of fibrin glue into the sinus (Fig. 17.13).

#### **17.6 Important Observations and Postoperative Care**

CSF drainage (about 150 cm3 /day) from the lumbar spinal tube should be continued for several

**Fig. 17.13** How to control bleeding from the cavernous sinus. (**a**) Bleeding from Mullan's anterolateral triangle (*arrow*). (**b**) Direct injection of fibrin glue into Mullan's triangle. (**c**) Bleeding from Dolenc's anteromedial triangle (*arrow*). (**d**) Application of Surgicel® soaked with

fibrin glue (*open triangle*). *ACP* anterior clinoid process, *II* optic nerve, *III* oculomotor nerve, *V1* ophthalmic branch of the trigeminal nerve, *V2* maxillary branch of the trigeminal nerve

days (3–7 days) after the operation to prevent CSF rhinorrhea, especially if the ethmoid sinus is opened during surgery.

#### **References**

**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

## **Surgery of Superior Cerebellar Artery Aneurysm (SCA)**

**18**

Miguel A. Arraez, Miguel Dominguez, Cristina Sanchez-Viguera, Bienvenido Ros, and Guillermo Ibañez

#### **18.1 Signs and Symptoms**

Patient a 57 years old male, a persistent headache was evaluated by neurologists. MRI was done, and incidental superior cerebellar artery (SCA) aneurysm was discovered after assessment of abnormal image at the lateral aspect of the mesencephalon. CT-angio and angiography (Fig. 18.1) showed an aneurysm with saccular form at proximal portion of right SCA. Endovascular treatment was precluded by neuroradiologist due to the morphological characteristics of the aneurysm's neck [1–3].

#### **18.2 Investigation**

The most striking neuroradiological examination was angiography and CT-angio. The superior cerebellar and posterior cerebral arteries were seen arising from a common origin ("N" type according to the McCullough classification of the anatomical variations of the circle of Willis) [4]. The aneurysm was close to the origin of the artery from basilar trunk at the anterior pontomesencephalic segment. The relation neck/dome suggested a good indication for surgery.

Viguera · B. Ros · G. Ibañez

Department of Neurosurgery, Carlos Haya University Hospital, Malaga, Spain e-mail<EMAIL_ADDRESS>
One of the important points before surgery is the appropriate anatomical characterization of the origin and location and morphology of the aneurysm. Among the segments of the SCA (prepontine, ambient, and quadrigeminal), the aneurysm was seen at the prepontine portion of the artery. It is noteworthy that in this segment, the SCA is giving off perforating branches to the pons before the origin of the lateral (marginal) branch. It is also interesting to mention that SCA aneurysms usually arise at the 2 mm proximal to the artery of origin (usually the basilar trunk). SCA aneurysms are not frequent (1.7% of the total), but 42% of the cases are found in the context of multiple aneurysms. Unlike our patient, the most common presentation is SAH (60%) followed by compression of III, IV, or V cranial nerve. The hemorrhagic presentation is frequently seen in lesions smaller than 7 mm.

#### **18.3 Preoperative Preparation**

Preoperative preparation is crucial in aneurysm surgery. Relaxation of the brain is of outstanding importance. The timing for surgery is decided in accordance to the clinical presentation (SAH, incidental aneurysm), morphology and size of the aneurysm, Hunt and Hunt scale, and choice of the surgical approach. Not infrequently posterior fossa lesions require significant brain retraction making advisable delayed procedure. In our

M. A. Arraez (\*) · M. Dominguez · C. Sanchez-

<sup>©</sup> The Author(s) 2019 149 J. July, E. J. Wahjoepramono (eds.), *Neurovascular Surgery*, https://doi.org/10.1007/978-981-10-8950-3\_18

**Fig. 18.1** Aneurysm of the right superior cerebellar artery in a 57-year-old male. Incidental finding. Angiography and CT-angio

patient (incidental aneurysm) elective surgery was done with preoperative spinal drainage and osmotic diuretics as perioperative adjunct measures.

#### **18.4 Steps of Surgery**

The approach selected for this case was a right frontotemporal craniotomy with limited zygomatic osteotomy (no need for orbito-zygomatic osteotomy in our opinion). The choice of approach for exposure of SCA aneurysm will depend on the segment where the lesion lies. The SCA might be separated into four segments: the pontine segment also called as anterior pontomesencephalic segment, the ambiens segment also called as the lateral pontomesencephalic segment, the quadrigeminal segment also called as the cerebellomesencephalic segment, and then the last one which is called cortical segment. According to location of aneurysm in one of these segments, the following approaches can be used: subtemporal, pretemporal extradural with clinoidectomy, subtemporal with addition of zygomatic or orbito-zygomatic osteotomy, and presigmoid and posterior fossa suboccipital. The latter is used to approach the cortical segment and the former to get access to the tentorial incisura and *perimesencephalic* segments of the SCA [5, 6].

In our patient, the lesion was placed at the pontine segment. This part of SCA is located between dorsum sellae and the upper brainstem [5]. This segment starts at the exit of the SCA from the basilar artery. The aneurysm in the presented case arose in this point (as very frequently seen in SCA aneurysms). In this area, special care must be taken as basilar artery and SCA at its origin show intermingled perforating vessels. Another relevant anatomical structure is the III nerve, constantly

**Fig. 18.2** Positioning of the head for the surgical approach to the right tentorial incisura. Left rotation and extension of the head. No hair shaving

above SCA and below the PCA (posterior cerebral artery). Due to location of aneurysm at the anterior pontomesencephalic segment, the choice of the approach was a subtemporal-pretemporal transzygomatic approach.

The patient was placed in supine position, with left rotation and slight extension of the head (Fig. 18.2). We usually do not shave the hair (previously prepared with antiseptic solution). A skin incision is made curvilinear from the hairline to anterior of tragus. After skin incision, the identification of the fascia at temporal is very important; there are superficial and deep layer of the fascia and dissection of the fat in between to avoid injury to facial nerve that innervates the frontal side. The zygomatic bone needs to be exposed. In our opinion, only a limited osteotomy is necessary to increase the reflection of the temporal muscle after detachment from the temporal bone (Figs. 18.3 and 18.4) instead of the more time-consuming orbito-zygomatic osteotomy that adds unnecessary morbidity. This maneuver diminishes the retraction of the temporal lobe increasing also the view of the tentorial incisura region. A frontotemporal craniotomy is done and dura is opened (Fig. 18.5). The brain is relaxed after mannitol and CSF release through spinal drainage or through opening the arachnoid layer at the basal cisterns in the context of the microsurgical approach. The intradural part of

**Fig. 18.3** Exposure of the zygomatic bone after careful dissection of the layers of the deep temporal fascia. A very limited zygomatic osteotomy is done instead of orbitozygomatic osteotomy (see the osteotomy lines depicted in upper left corner)

**Fig. 18.4** Reflection downward of the temporal muscle exposes adequately the temporal bone to increase the temporal component of the craniotomy

the operation starts with a very minimal retraction just to hold the temporal lobe. The tentorial incisura is exposed with the relevant structures. The exposure will allow the recognition of the anterolateral mesencephalon, carotid artery, posterior communicating artery and its perforating arteries, PCA, SCA, and oculomotor nerve, typically running below PCA and above SCA (Fig. 18.6). Also, IV nerve can be seen in its typical course along tentorium [7].

All these steps were done in our patient. The III nerve was right in the direction of our sight,

**Fig. 18.5** Right frontotemporal craniotomy. The frontal component is small. The temporal flap almost reaches the level of the middle fossa floor to diminish the intradural retraction of the temporal lobe

**Fig. 18.6** Exposure of the right tentorial incisura and pontomesencephalic segment of the SCA. Temporal lobe retracted (1), tentorium (2), posterior cerebral artery (3), basilar artery (4), III nerve interposed in the direction of the sight of the surgeon (5), right mesencephalon (6), and aneurysm dome right before clipping

making slightly difficult in the identification and clipping of the neck. A Sugita clip was use to exclude the aneurysm from the circulation (Fig. 18.7). The effectiveness of the procedure was confirmed by means of ICG intraoperative angiography (Fig. 18.8).

**Fig. 18.7** SCA aneurysm clipped. The SCA main trunk has been preserved (1)

#### **18.5 Expert Opinion/Suggestion to Avoid Complication**

One of the possible complications would come from bad exposure due to wrong choice of the surgical approach [8, 9]. Wrong approaches very seldom happen, at the anterior circle of Willis, but the posterior circle offers many more possibilities and difficulty to reach appropriately the aneurysm neck. The anatomy of the vessels and their variations along with morphology of the aneurysm, its neck, and relation with perforating vessels are of course of paramount importance. Thus, preoperative assessment (angiography, CT-angio) is absolutely crucial to establish the choice of the approach [10, 11]. The segment in which the aneurysm is located and the relation of the aneurysm and posterior clinoid must be carefully evaluated. The segment harboring the lesion will suggest anterior, lateral, or posterior approach. In regard to the relation of the aneurysm and posterior clinoid, a very low origin would preclude the use of anterior intradural approaches.

**Fig. 18.8** ICG intraoperative angiography before (**a**) and after clipping (**b**) showing exclusion of the aneurysm. Basilar artery (1), posterior cerebral artery (2), superior cerebral artery (3), SCA aneurysm (4), and III nerve interposed (5)

Another frequent source of complications in *para-temporal* approaches is the improper management of the temporal lobe (contusion, infarction, hemorrhage). In our selected approach (anterolateral), a very gentle retraction of the temporal lobe must be done lifting the tip not subtemporally but anteriorly. No veins are encountered in a long avenue from the sylvian fissure (anterior and medial) to the Labbé area (posterior and lateral). This lifting of the temporal lobe is very well tolerated unlike some other forms of compression or distortion. Sylvian fissure usually doesn't need to be opened. Care must be taken not to tear sylvian veins during the exposure. The proper extension of the head and gravity can help diminish any harmful effect of the retractors over the temporal lobe.

#### **18.6 Postoperative Measures**

This approach doesn't differ from other approaches in regard to the general care after other aneurysm surgery procedures or craniotomy. We administer postoperative calcium antagonist, antiepileptic drugs, and low weight subcutaneous heparin along with early mobilization. The external lumbar drainage is removed 24 h after surgery.

#### **References**

1. Chaloupka JC, Putman CM, Award IA. Endovascular therapeutic approach to peripheral aneurysms of the superior cerebellar artery. AJNR Am J Neuroradiol. 1996;17:1338–42.

**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

**19**

## **Surgery of Posterior Inferior Cerebellar Artery (PICA) Aneurysm**

Ivan Ng and Julian Han

#### **19.1 Sign and Symptoms**

Posterior circulation aneurysms account for approximately 10% of all aneurysms, which affect 1–6% of the population [1, 2]. Aneurysms of the posterior inferior cerebellar artery (PICA) are very rare, only 0.5–3% of all aneurysms [3]. Patients with PICA aneurysms usually present with subarachnoid hemorrhage, or they might have symptoms due to compression of the brainstem or lower cranial nerves. Microsurgical clipping of PICA aneurysms is difficult and very challenging due to the limited working space and its surrounding neurovascular structure, the brainstem and lower cranial nerves IX, X, XI, and XII, and very often the aneurysm is located very deep and far from the surgeon's view. Surgical maneuvers require moving around and sometimes in between cranial nerves. PICA aneurysms may vary widely within a range in terms of their complex anatomy, as a result either of their origin, branching out of the vertebral artery (VA), or their course along the lower cranial nerve. The PICA itself is usually of a small caliber, and aneurysms on it with a wide neck create a difficult situation with respect to clipping the aneurysm and preserving the PICA.

National Neuroscience Institute (NNI), Singapore, Singapore e-mail<EMAIL_ADDRESS>
#### **19.2 Investigation and Vascular Anatomy**

The VA branches out of the subclavian artery, ascends along the lateral aspect of the cervical vertebra through transverse processes, turns posterior of the lateral mass of C1, and enters the subarachnoid space between foramen magnum and ring of C1. The initial part of the intradural VA passes the superior–anterior to the first cervical roots, then crosses in front of the dentate ligament, also in front of the accessory nerve at the spinal part. The VA then ascends in front of the hypoglossal nerve to reach the medulla at its anterior surface, where it meets and unites with the contralateral VA to become the basilar artery at the junction of the medulla and pons.

The PICA is the VA's largest and most clinically significant branch. The PICA is very complex, sometimes long and tortuous, having a variable course and a wide area of supply compared to other branches of the cerebellar arteries. It supplies the medulla, cerebellar tonsil, inferior part of the vermis, and inferior surface of the cerebellar hemisphere. The PICA has five segments: anterior medullary (p1), lateral medullary (p2), tonsillomedullary (p3), telovelotonsillar (p4), and cortical (p5) segments (Fig. 19.1).

The first segment (p1) starts from the PICA's origin just in front of the medulla near the inferior olivary, then turns posteriorly through hypoglossal rootlets and continues on, then

I. Ng (\*) · J. Han

<sup>©</sup> The Author(s) 2019 155 J. July, E. J. Wahjoepramono (eds.), *Neurovascular Surgery*, https://doi.org/10.1007/978-981-10-8950-3\_19

**Fig. 19.1** Drawing of PICA and its segments: anterior medullary (p1), lateral medullary (p2), tonsillomedullary (p3), telovelotonsillar (p4), and cortical (p5) segments. It supplies the medulla, cerebellar tonsil, inferior vermis, and suboccipital surface of the cerebellar hemisphere

turning to the lateral surfaces of the medulla. The second segment (p2) starts from the turn at the prominent point of the olivary until the outlet of the lower cranial nerve. The third segment (p3) starts at the outlet of the lower cranial nerve and crosses medially at the posterior aspect of the medulla, making a big loop starting from the lateral surface of the tonsil until it reaches the pole and turning up at the medial surface of the tonsil. The fourth segment (p4) starts at the midpoint of the PICA at the medial surface of the tonsil, moves toward the fourth ventricle roof, then comes out through the fissure to reach the cerebellar surface. There is almost always a cranial loop where the apex usually overlies the inferior part of the medullary velum. The fifth segment (p5) starts where the PICA extends out from the fissure between the tonsil, vermis, and cerebellar hemisphere. It often happens that the bifurcation of the PICA occurs at this fifth segment; the lateral trunk will supply the tonsil and cerebral surface, while the medial trunk will supply the vermis.

CT angiography and 3D reconstruction are usually sufficient for diagnostic purposes and surgical planning. Interventional angiography is rarely required, but for selective cases it still provides additional value for treatment.

#### **19.3 Steps in Surgery**

Microsurgical treatment of PICA aneurysms could be done either by clipping the aneurysm or trapping/occluding it with bypass surgery.

PICA aneurysms most commonly occur at the p2 and p3 segments [4]. Common approaches include by the lateral suboccipital or far lateral suboccipital for more proximal PICA aneurysms and paramedian or midline suboccipital for more distal PICA aneurysms. Other more complex skull-base approaches have also been described, such as retro-labyrinthine presigmoid and transsigmoid exposures. A modified far lateral approach, which has been the approach most frequently used by the senior author in dealing with PICA aneurysms, is described here.

The patient may be placed in a true lateral position, with the operative side facing upward (Fig. 19.2). The dependent extremity is hung in a sling. The contralateral shoulder is pushed forward anteriorly, and there is mild inferior traction of the shoulder with tape. The vertex of the head is tilted slightly toward the ground, and there is also a slight lateral rotation of the head toward the ground. This opens up the working space at the lateral suboccipital region. Skin incision is made in the manner of golf club with the descending limb remaining at the midline from inion to C2. The muscles and soft tissue are dissected with monopolar blade then retracted, exposing the occipital, mastoid bones and posterolateral arch of C1; when dissection is done near the foramen magnum, especially 2–3 cm laterally from the midline, where yellowish fat tissue occurs, one must be careful not to injure the extracranial VA. Place a burr hole near the transverse–sigmoid junction, gently detach the dura from the bone, and perform a craniotomy up to 1 cm from the midline and the foramen magnum inferiorly; additional C1 laminectomy is necessary for better

**Fig. 19.2** *Left*: Patient is placed in lateral position with operative side upward. The dependent extremity is hung in a sling. The contralateral shoulder is pushed forward anteriorly, and there is mild inferior traction of shoulder

with tape. *Right*: Vertex of head is tilted slightly toward ground, and there is also a slight lateral rotation of head toward ground

proximal control. Lateral suboccipital bony exposure should be up to the line where the VA enters the dura. The dura opening is a gentle curve and the edges are holded with silk stiches. The Cerebrospinal fluid needs to be released slowly so the brain is relaxed, and everything must be done under a microscopic view. Preparing the vertebra artery (VA) for the proximal control and usually the VA is under the dentate ligament when it comes to intracranially. The ligament must be cut gently from the foramen magnum and at C1 to enable viewing of the VA anteriorly and to widen the surgical corridor by detaching the upper cervical spinal cord. The proximal VA just after it becomes intracranial should be prepared for temporary clipping. In cases where the PICA originates right at the point where the VA pierces the dura, extradural/extracranial dissection of the VA may be performed. Typically, authors expose the VA at the point where the vessel forms a groove in the upper surface of the C1 lamina, which is marked anatomically by the sulcus limitans. Dissection of the PICA should not be a difficult procedure; in fact, it is relatively simple, and one should be able to locate the aneurysm by simply following the PICA's course. We can start following the PICA just under the tip of the tonsil and tracking it to the cistern. Sharp dissection may be done by opening the arachnoid layer to expose the vagoaccessory triangle, which provides a good natural working space, and many surgeons use this method in a far lateral approach (Fig. 19.3). Superiorly there is the vagus nerve, laterally the accessory nerve, and medially the medulla. One's view of the meeting point of the VA and PICA is usually obstructed by the IX–X–XI complex. Each case may have unique features, such as the shape of the aneurysm, the parent artery anatomy, and the tortuosity of the vessel, so the dissection strategy, including the pathway, should be formulated accordingly.

For more distally positioned aneurysms, surgical access may be achieved using a telovelar approach (Figs. 19.4 and 19.5).

PICA aneurysms are often associated with unusual anatomy, and direct clipping is not always possible. Several factors such as the branch anatomy, the size of the aneurysm, dolicho-ectatic morphology, or even atherosclerotic neck, will contribute to the difficulty. This then requires alternative techniques such as a trapping and

**Fig. 19.3** (**a**) This patient has a proximal left PICA aneurysm in lateral medullary zone. The approach is via a modified far lateral approach. (**b**) The dissection is deep to

the rootlets of the accessory nerve to expose the aneurysm neck. (**c**) The aneurysm was clipped simply with a bayonet clip

bypass procedure. Preoperative study and planning are very important if revascularization procedures are necessary. This is particularly significant in proximally located aneurysms, particularly at the VA–PICA junction. In scenarios potentially requiring the occlusion of the PICA, bypass procedures may be necessary.

There are various options of extra-intracranial (EC-IC) bypass surgery. However, Authors generally favor an in situ bypass (PICA–PICA) that matches donor and recipient arteries well because it can be performed quickly.

Bypass options include the following (Fig. 19.6):

**Fig. 19.4** (**a**) Some PICA aneurysms are located more distally, such as this one, at the ascending loop of the p3 segment of the left PICA. This is better accessed via a midline suboccipital approach. (**b**) Proximal and distal

control was achieved with temporary clipping, before dissecting out the aneurysm neck. (**c**) The aneurysm was clipped simply with a straight clip

PICA–PICA bypass involves the using two PICAs that lie close to each other at the midline in the ascending portion of the p3 segment running at the medial surface of the tonsil. The two loops are generously mobilized and their arachnoid trabecula is cut to make the vessel free

**Fig. 19.5** (**a**) This is a case of proximal right PICA aneurysm located at the lateral medullary segment. Dissection was via a modified far lateral approach. Intradural VA was

identified for proximal control. (**b**) Aneurysm neck excised just beyond the traversing accessory nerve. (**c**) The aneurysm neck was obliterated with tandem clipping

and to allow for tension-free side-to-side anastomosis. With the temporary clips in place on both PICAs, a longitudinal arteriotomy is made in each artery, ideally two to three times the PICA diameter. Both PICAs should have almost identical diameters, or the donor should be larger than the ipsilateral recipient.

Reimplantation of the PICA can be done if the clip obliteration of the aneurysm also sacrifices the PICA but preserves the VA. The occluded PICA can be revascularized by cutting at its origin, transposing and reimplanting it proximally to the original PICA origin. This is an end-to-side anastomosis. Reimplantation is probably the

**Fig. 19.6** Drawing of PICA–PICA bypass (*left*), reimplantation of PICA to VA (middle), and reanastomosis of PICA (*right*)

hardest of the IC–IC bypasses because the location is deep and it is surrounded by all the lower cranial nerves. The complication of postoperative lower cranial nerve palsy is much higher with this surgery.

Reanastomosis involves reconnecting the transected ends of a parent artery after excising the aneurysm; it is an end-to-end anastomosis. The afferent and efferent ends are generously mobilized from their arachnoid adhesions to allow approximation without tension. A PICA's tortuosity usually provides adequate length to get to the arteries without tension. Ideal situations for such a bypass include aneurysms that are fusiform in their distal portions and have no branches. The end-to-end anastomosis line is shorter, making suturing quicker.

Large complex aneurysms at the VA–PICA junction may be trapped and reconstructed with an interposition graft using the radial artery. The donor site is usually at V3, and the recipient site is a PICA. A radial artery graft is more suitable in terms of caliber compared to a saphenous vein graft. Interposition means that two grafts are needed, with both requiring two anastomoses, either end to end or end to side.

An alternative bypass is an OA–PICA bypass for large complex aneurysms involving the VA– PICA junction. The OA is located at the posteriormost of the eight branches of the External Carotid artery and lies medially and posteriorly of the mastoid process. It is identified preoperatively using a handheld Doppler probe. It is usually densely adhered to its surrounding muscular tissue, making it more difficult to dissect compared to the Superficial Temporal Artery. It is an endto-side anastomosis.

Parent artery sacrifice of the PICA is a possible treatment, but it may cause medullary and cerebellar infarcts that will be followed by malignant edema, causing acute hydrocephalus or, in the worst case, direct brainstem compression. These complications may be tolerable if the patient's condition deteriorates, in which case urgent decompressive craniectomy may become necessary. Many surgeons might simply sacrifice the parent artery without revascularization if the aneurysm arises at the most distal two segments of the PICA [5]. The more proximally parent PICA should not be sacrificed because of variations in perforating vessels that may arise from more proximal segments. Liew et al. have suggested that if an aneurysm is located distally to the last perforator artery, then a clip may be safely placed on the parent artery after the perforator artery [6]. If there is no evidence that the patient will be able to tolerate PICA sacrifice, the surgeon will need to prepare all alternatives, including direct clipping with or without bypass to preserve the PICA; additional endovascular coiling will likely be required to achieve complete aneurysm occlusion [7].

#### **19.4 Expert Opinion**

PICA aneurysms are relatively rare and pose significant challenges to neurosurgeons owing to their proximity to critical structures and their variable complex anatomy. However, they can be successfully managed microsurgically, and the neurosurgeon has a variety of options at her disposal that can be used aside from direct clipping, such as occlusion or trapping, with several bypass possibilities.

#### **References**

**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

## **Surgery of Giant Aneurysm**

**20**

Petra Wahjoepramono and Eka J. Wahjoepramono

#### **20.1 Sign and Symptoms**

Aneurysm bigger than 25 mm is called giant aneurysm [1], further subdivided by morphology into saccular, fusiform, or dolichoectatic aneurysms [2]. Epidemiologically, they are very rare, comprising only 0.5% of all intracranial aneurysms, while others describe it as 3–5% of all intracranial aneurysms [1, 3, 4]; the epidemiology of intracranial aneurysms among the general population amounts to 0.2–9.9% [5]. In pediatric patients, the incidence of giant aneurysms and aneurysms of the posterior circulation is greater than those in adult patients [6]. The most common type is the saccular giant aneurysm, accounting for 98% of cases [7]. Fusiform types are more commonly found in the posterior circulation and MCA [1]. These lesions have a female preponderance and are diagnosed mostly between 40 and 60 years of age [2]. These lesions are found

Department of Neurosurgery, Medical Faculty of Universitas Padjadjaran, Hasan Sadikin Hospital, Bandung, West Java, Indonesia

Department of Neurosurgery, Faculty of Medicine Universitas Pelita Harapan (UPH), Neuroscience Centre Siloam Hospital Lippo Village, Tangerang, Indonesia

E. J. Wahjoepramono (\*)

J. July, E. J. Wahjoepramono (eds.), *Neurovascular Surgery*, https://doi.org/10.1007/978-981-10-8950-3\_20

most often in the anterior circulation, affecting the ICA, MCA, and ACA [1, 2], while in the posterior circulation, they most commonly occur at the basilar artery, vertebrobasilar junction, PCA, and PICA [2]. Multiple giant aneurysms can be found in 7% of patients [2].

The most common presenting symptoms for these lesions are mass effect complaints, seizures caused by irritated neural tissue, or compression of cranial nerves [2, 4], which are very different from the subarachnoid bleed usually found in smaller aneurysms [2, 4]. Additionally, the occurrence of thrombus formation in these aneurysms may produce symptoms of thromboembolic event in the parent vessel or perforator vessels [2]. Thromboembolism may occur in up to 60% of giant aneurysms, and its probability increases along with aneurysm size. Hydrocephalus had been reported due to the compression of giant aneurysms near the cerebral aqueduct, and carotid-cavernous fistulae (CCF) can result from ruptured aneurysms of the ICA cavernous segment [2].

#### **20.2 Investigation**

These aneurysms must be thoroughly investigated as to its vascular anatomy, such as the presence of perforators, the size and orientation of the aneurysm neck, and its distal outflow (Fig. 20.1). Giant aneurysms frequently display calcification,

P. Wahjoepramono

Department of Neurosurgery, Faculty of Medicine Universitas Pelita Harapan (UPH), Neuroscience Centre Siloam Hospital Lippo Village, Tangerang, Indonesia

**Fig. 20.1** *Left:* Three-dimensional CT scan of a 50-year-old, female with left M1 giant aneurysm. *Right:* Intraoperative finding after a wide sylvian fissure dissection

thrombosis, and wall thickening around the neck, while there may be multiple perforator vessels present from the parent artery or even from the aneurysmal sac in the case of fusiform aneurysms [4]. The gold standard diagnostic procedure would be digital subtraction angiography (DSA), which provides the best picture of cerebrovascular anatomy and provides information about the suitability for vessel bypass. DSA can be combined with CT angiography to provide information about surrounding bony anatomy for surgical approach and monitor the presence of calcified thrombus. CT scan is very useful in evaluating for calcification [1], and MRI may be performed if there is a suspected ischemic event, to investigate peritumoral edema and to evaluate intraluminal thrombus [1]. Preoperative assessment of these patients includes balloon occlusion tests during angiography, if the surgeon plans to sacrifice the ipsilateral ICA [2]. Intraoperatively, patients may be monitored using electroencephalography (EEG) to detect any changes in the electrical activity, as well as continuous transcranial Doppler (CTD) to check the cerebral blood flow [2].

The natural course of giant unruptured aneurysm has been previously reported by Wiebers et al. [8]; in anterior circulation the 5-year cumulative risk is about 40%, while in the posterior circulation including posterior communicating artery, the risk is about 50%. A study by ISUIA (International Study of Unruptured Intracranial Aneurysms) group shows the rupture rate at 6% in the first year after diagnosis alone [5, 9], with a more recent study by the UCAS Japan investigators reporting a rupture risk of giant aneurysms at 76.26% within 3 years [3], with aneurysms at the posterior and anterior communicating arteries being more likely to rupture [3, 5, 9]. The mortality rate of such ruptures reaches 20–70% [10, 11], reaching higher than 60% within 2 years of diagnosis [12]. It is therefore established that such rupture rates were similar or worse to the risks taken when a similar lesion is treated, either through surgery or endovascular treatment. More recent studies on the natural course of aneurysms have not found any other parameters indicative of rupture risk [13].

#### **20.3 Steps of Surgery**

#### **20.3.1 Surgical Approach**

Microsurgical clipping has the advantage of being able to relieve mass effect associated with nerve compression, especially in aneurysms with thrombus formation or atheroma [14]. The main principles of giant aneurysm surgery are to prepare the proximal and distal control, avoid the blunt dissection, and appreciate all the perforators, and to achieve circumferential dissection of the aneurysm might be very difficult [12]. The goals of surgical management of giant aneurysms are:

Several microsurgical techniques which are used in the management of giant aneurysms include: microsurgical clipping, bypass of parent artery (ICA) using saphenous vein graft or the MCA, temporary ligation of the ICA to help clipping, aneurysm wrapping with muscle or fascia, or combined microsurgical and endovascular treatment [2].

Microsurgical clipping of giant aneurysms can be performed, because all aneurysms must have a "neck." [4] With the use of fenestrated clips, aneurysms with large necks can undergo vessel reconstruction to create an aneurysm neck [4] (Fig. 20.2). The presence of perianeurysmal edema, which is most often found in the MCA circulation, may complicate the microsurgical clipping [16].

There are several approaches available for microsurgery of giant aneurysms of the carotid artery or the basilar tip; an approach through the middle fossa is recommended. The important surgical anatomy in this region is the cavernous sinus, which includes several natural corridors available to access this region, usually divided into the ten triangular spaces [2]. Skeletonization of the ICA in the carotid canal through Glasscock's triangle [12] is performed to treat intracavernous aneurysms [2]. Orbito-zygomatic approach is used to maximize exposure [12].

Certain location of the posterior circulation aneurysm could be approach through subtemporal such as the upper basilar artery segment [2]. The transpetrosal approach or far-lateral approach may be used for lower lesions [12, 17].

To reduce mass effect of the giant aneurysm after clipping is performed, the aneurysm dome can be directly punctured to exsanguinate the sac when no thrombus is present and perform suction decompression [4, 12] (Fig. 20.3). If there is thrombus, calcification or atheroma is present, thrombectomy may be performed on the aneurysm sac, also called endoaneurysmectomy [4].

**Fig. 20.2** *Left:* Same case of Fig. 20.1 shows intraoperative view of giant aneurysm undergoing vessel reconstruction with multiple fenestrated clips. *Right:* Angiography confirmation of MCA flow

**Fig. 20.3** Aneurysm deflation using the wing needle no 25G

Aneurysm repair using wrapping or clip wrapping with the muscle or fascia can be used to maximize outcomes in ruptured aneurysms [12]. Aneurysms which are broad-based, frail, or complex may also be clipped using augmented "cotton-clipping" technique [18]. This technique can also be used to perform emergency repair in the case of ruptured aneurysm.

Low-flow and high-flow bypass techniques have been used to provide revascularization of the distal circulation in the treatment of giant aneurysms [4]. Vessel reconstruction using clips also serve the same function, which is to guarantee CBF distal to the aneurysm [4].

Microsurgical treatment may be advantageous in comparison with endovascular treatment in cases of complex basilar artery aneurysms. Performing surgical clipping of the aneurysm may provide selective occlusion of the basilar artery aneurysm while avoiding damage to the thalamoperforators which may adhere to the posterior aspect of the aneurysm, compared to endovascular treatment where visualization of the perforators cannot be achieved, and the risk of brainstem damage due to ischemia is greater [19].

Adjunctive techniques which can be used in giant aneurysm surgery include deep hypothermic circulatory arrest (DHCA) [4, 20, 21] and the use of excimer laser-assisted nonocclusive anastomosis (ELANA) bypass [22, 23]. DHCA may be performed to temporarily reduce blood flow to the aneurysm, facilitating the surgeon to perform surgical clipping and neck reconstruction. However, it has several drawbacks, including unpredictable recovery after circulatory arrest and possibility of postoperative brain hemorrhage [24]. A study by Ponce et al. also shows significant mortality and morbidity rates for using DHCA, even though most patients had improved neurological function after surgery [21]. Neuroprotective agents may also be used to improve outcome after surgery, especially if DHCA will be used. Barbiturates are traditionally used to reduce cerebral blood volume and metabolism before the ischemic procedure [12].

The ELANA technique enables surgeons to perform a high-flow bypass without utilizing temporary clips, which makes it a reasonable alternative to other methods of direct revascularization, such as direct anastomosis [23]. The elimination of temporary clips from the procedure provides the surgeon with longer safe operating time without cerebral ischemia and eliminates the need of exposing the proximal parent artery before the procedure, which is especially beneficial in the posterior fossa [23].

#### **20.3.2 Endovascular Approach**

Endovascular management has the advantage of decreased morbidity, due to its nonsurgical nature [25]; aneurysms at the posterior circulation especially show higher morbidity after microsurgery [26]. The endovascular management of giant aneurysms can be performed as long as the aneurysm does not show signs of intraluminal thrombus; if there is thrombus, then endovascular management will not be able to relieve the mass effect caused by the aneurysm itself, even though it could occlude the aneurysm from the circulation.

The endovascular management for giant aneurysms are [25]:

Parent vessel occlusion is a very simple technique which is guaranteed to exclude the aneurysm from cerebral circulation [4, 25]. This is the endovascular treatment of choice if the patient can tolerate parent vessel occlusion [25]. Multiple tests must be done before this treatment, using balloon occlusion test, to ensure that the cerebral circulation is not compromised by blocking the parent artery [25]. A study by Linskey et al. demonstrated that even without previous BOT, up to 75% of patients can tolerate ICA occlusion [28]. The vertebral artery, however, can be safely occluded, except where the patient only has a single vertebral artery without a patent PCoA [25].

Selective occlusion of giant aneurysms, whether using coils or ONYX embolization device, emphasizes on filling the aneurysm lumen and occluding the aneurysm from the circulation as thrombus forms within the lumen [25]. As most giant aneurysms are formed with large necks, coil-assisted devices such as stents, balloons, or flow diverters are often used [25]. The re-endothelialization of the parent artery after such a procedure is key to preserving a patent lumen and reducing reopening of the aneurysm [29].

Another treatment option is to use flowdiverting stents [4]. These devices have more metal coverage and lower porosity in comparison with standard intracranial stents and have the capability of creating blood flow inside their artificial lumen and induce thrombus formation in the dome of giant aneurysms as blood flow into the dome decreases. These stents are also capable of providing a scaffold for neointimal growth in the vessel. The role of flow diverters against giant aneurysms is effective, with permanent major complication occurring in 3% of patients in a study by Piano et al. [30] and 5–10% of patients in other studies [31]. Previous studies have documented encouraging results when these stents are used against aneurysms of the anterior circulation [32, 33], defined as aneurysms from the ICA below the anterior choroidal artery. However, they are not as effective against aneurysms in the vertebrobasilar system [34]. It is thought that the vertebrobasilar system with its many perforators are not suitable for flow-diverting stents, as these stents also occlude the perforators, in some cases up to 2 years after stent placement [34]. The resulting ischemia of the pons may lead to unacceptable morbidity [34]. These devices may also be used in conjunction with coils to achieve complete occlusion of the aneurysm [35].

The main concern about selective occlusion is that the embolization device may disengage over time, either by coil become compaction, the coil sometimes migrate, degeneration of the thrombus intraluminal or migration of the ONYX clot into the parent artery [25, 26, 36]. This problem is caused by the inherent nature of giant aneurysms, with their large lumen volume, which sometimes cannot be adequately packed with these devices [25, 26]. Stable occlusion of these aneurysms requires at least 25% packing of its volume, which is difficult to achieve with large-volume aneurysms [25]. In a study by van Rooij et al. [25], it is found that nearly all giant aneurysms show reopening after endovascular treatment in the 6-month postoperative period, even up to several years of stable condition. The follow-up strategy for these patients is to schedule additional coiling procedures along with routine follow-up, with decreased patient compliance as a result [25, 37]. MRA has also been suggested as a routine follow-up procedure after endovascular treatment [37].

#### **20.4 Expert Opinion/Suggestion to Avoid Complication**

In several cases such as paraclinoid giant aneurysms, combined approach using microsurgical and endovascular management can be performed [38]. Paraclinoid giant aneurysms are often atherosclerotic and calcified, difficult exposure and dissection of the aneurysm dome, and difficulty in exposure and proximal control through temporary clipping [38, 39]. In such cases, temporary occlusion of the parent artery can be achieved through the endovascular method, while microsurgery is used to expose and clip the tumor, followed with suction decompression of the aneurysm dome [4]. Flow alteration using a combined microsurgical and endovascular method may be used to treat fusiform basilar artery aneurysms [40]. Sughrue et al. [18] championed a combined approach using microsurgery and endovascular therapy as an adjunct in the treatment of giant aneurysms.

#### **References**

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**21**

## **Surgery of Posterior Fossa AVM**

Ferzat Hijazy, Mardjono Tjahjadi, Aruma O'shahinan, Hanna Lehto, Hugo Andrade, Behnam Rezai Jahromi, Johan Marjamaa, Aki Laakso, Martin Lehecka, and Juha Hernesniemi

#### **21.1 Signs and Symptoms**

Prior to the routine use of vertebral angiography, posterior fossa AVMs were usually found unexpectedly during the evacuation of posterior fossa hematomas [1]. In 1932 (May 5th), Olivecrona had reported their first successful radical removal of a left cerebellar AVM in a 37-year-old male who was misdiagnosed of having a posterior fossa tumor. After an 8-h-long marathon surgery under local anesthesia and with a blood transfusion of 2000 ml, the AVM was removed. The postoperative course was uneventful and the patient left the hospital 3 months later [2]. As vertebral angiography became more widely used, the preoperative diagnosis of posterior fossa AVMs became possible. Even so, at that time, neurosurgeons thought that it was possible to operate on small-to-moderate-sized AVMs in silent areas of the brain but were reluctant to touch AVMs in nonsilent areas [2], including the more demanding posterior fossa. Neurosurgeons were, however, disappointed that only very few AVMs could be removed entirely without great

F. Hijazy · M. Tjahjadi · A. O'shahinan · H. Lehto

H. Andrade · B. R. Jahromi · J. Marjamaa · A. Laakso M. Lehecka · J. Hernesniemi (\*)

Department of Neurosurgery, Helsinki University Central Hospital, Helsinki, Finland

e-mail<EMAIL_ADDRESS><EMAIL_ADDRESS><EMAIL_ADDRESS><EMAIL_ADDRESS><EMAIL_ADDRESS>
risk, which led to the development of other, ineffectual techniques, such as vertebral artery or feeder ligation [1].

In 1961, based on a review of literature and his personal experience, Verbiest showed that small cerebellar AVMs could be removed safely. However large posterior fossa AVMs, even if located outside the brainstem, could be extremely dangerous to operate on, while brainstem AVMs were considered inoperable lesions by their nature [3]. Since that report, the frequency of successful surgical removal of the posterior fossa AVMs has increased with the development of new microsurgical and radiological techniques, modern neuroanesthesia, and refined intensive care principles. Later, Drake with his big series reported that removal of the posterior fossa AVMs even in the more sensitive areas of the hindbrain could also be accomplished with excellent outcomes.

Over the last 30 years, around 1000 patients with AVMs have been treated in two centers in Finland (Helsinki and Kuopio); one tenth of them were posterior fossa AVMs. The accumulated experience in the treatment of these patients is documented in this chapter, as well as the philosophical and practical basis for our current management of these relatively uncommon lesions.

All types of AVMs contribute about 2% of all hemorrhagic strokes. When AVM rupture occurs, it usually affects young adults in third or fourth decade of their life, more often males than

J. July, E. J. Wahjoepramono (eds.), *Neurovascular Surgery*, https://doi.org/10.1007/978-981-10-8950-3\_21

<sup>©</sup> The Author(s) 2019 171

which is about 1/10 of that of cerebral aneurysms. Posterior fossa AVMs are even more uncommon, and it can be roughly concluded that 1/10 of cerebral AVMs are located in the posterior fossa [1].

#### **21.1.1 Location**

The posterior cranial fossa is the largest and deepest of the three cranial fossae, which extends from the tentorial incisura superiorly to the foramen magnum inferiorly. The major contents of it are the cerebellum and the brainstem which consist of the midbrain, the pons, and the medulla oblongata. Posterior fossa AVMs can be generally classified into brainstem (25%), cerebellar vermian (15%), superficial cerebellar hemispheric (40%), and deep cerebellar hemispheric (20%) lesions based on the dominant location of the nidus.

Of the 631 AVM patients admitted to Helsinki University Central Hospital between 1942 and 2005, a total of 64 patients were diagnosed with infratentorial AVMs (Table 21.1).

#### **21.1.2 Signs and Symptoms**

In many studies, including ours, hemorrhage is the main clinical presentation of the posterior fossa AVMs accounting for 72–92% of the patients [1, 2, 4–7]. The type of hemorrhage depends on the location of the AVM, e.g., cerebellar AVM cases often come with intraparenchymal hemorrhage, cerebellopontine angle (CPA) AVMs are highly related to subarachnoid hemorrhage, and brainstem AVMs are more likely to cause subarachnoid and intraventricular hemorrhage (Figs. 21.1 and 21.2a). We have earlier reported that the annual rupture rate of posterior fossa AVMs within 5 years after admission is almost three times higher than in their supratentorial counterparts (11.6% vs. 4.3%) [8].

**Table 21.1** The locations of the posterior fossa AVMs [4]

**Fig. 21.1** Axial CT scan shows ICH due to AVM rupture, and posterior circulation DSA (lateral view) shows the location of the AVM

**Fig. 21.2** (**a**) CT scan of the brain shows SAH and intraventricular bleeding due to posterior fossa AVM with associated aneurysm confirmed by left vertebral artery

DSA (**b**). (**c**) Post-op DSA illustrates complete surgical removal of the AVM and clipping of the associated aneurysms

The risk factors for hemorrhagic presentation of AVMs in general based on studies from the Finnish population are young age, AVM, deep venous drainage, previous rupture, and infratentorial and deep location. Small AVM size tends to have a higher risk for hemorrhagic presentation in almost every series, while large AVM size is also a factor for AVM rupture in most multivariate analyses (including ours) [8, 9]. Some multivariate analyses didn't find large size as a risk factor for AVM rupture, but importantly, small AVM size has never been found as a prospective risk factor for rupture in a multivariate analysis. That is because the small AVMs will not be diagnosed unless they are ruptured, whereas many large ones become symptomatic even before the hemorrhage [10, 11]. AVM-associated aneurysms are found as risk factor for hemorrhage in many meta-analysis studies [10–12]. This risk is highest for the first few years after diagnosis, then it declines, but overall it remains significant for decades [13].

Other clinical presentations are relatively uncommon and depend on the location of the AVM. Cerebellar AVMs are more likely to cause headache, hydrocephalus, and gait disturbances. CPA AVMs may give symptoms of cranial nerve compression such as trigeminal neuralgia or hemifacial spasm. Brainstem AVMs can cause significant neurologic deficits even in the absence of hemorrhage probably due to local mass effect, vascular steal phenomenon, or venous congestion. Overall, progressive neurologic deficits, cranial nerve palsy, headache, and ataxia are possible symptoms of posterior fossa AVMs [1, 7]. In recent years the incidental finding of posterior fossa AVMs has also become more common with the increasing use of modern imaging techniques, making incidental AVMs to account for to 10% in recent studies, compared to that of less than 2% in early studies [14].

#### **21.2 Investigation**

Since the most common clinical presenting sign of posterior fossa AVM is an acute hemorrhage, a computed tomography (CT) scan is the most commonly used initial imaging modality. Location, volume, and mass effect of the hemorrhage can be detected quickly with a CT scan as well as signs of hydrocephalus. Any evidence of a previous bleeding or calcification raises the possibility/probability of an AVM as the origin of the hemorrhage (Fig. 21.1). Contrast injection may show feeding arteries and draining veins as linear, vermiform, tubular, or serpentine highdensity areas.

Magnetic resonance imaging and angiography (MRI and MRA) provide exquisite detail of the anatomic relations of the AVM. This is particularly useful when the AVM lies in or near the brainstem or cerebellar peduncle, in order to determine the operability or to plan the surgical approach. MRI is superior to other investigations in defining the nidus size and its location in relation to the surrounding structures. Nidus of the AVM is seen as an area of signal void and may have a honeycombed pattern (Fig. 21.3). Tubular signal void structures converging on the nidus represent the feeding arteries and draining veins. Bony artifacts are avoided with MRI, allowing therefore better identification of superficial supply to, or superficial drainage from, the AVM. Gliosis and infarction surrounding the nidus are shown with the hyperintensity area in T2 and FLAIR on MRI. MRI is however an impractical imaging technique for critically ill patients, for example, those harboring a cerebellar clot.

Digital subtraction angiography (DSA) imaging is essential for all patients with AVMs in order to exactly delineate the vascular structures comprising the AVM and for the subsequent management. With DSA the feeding arteries and draining veins can be visualized (Fig. 21.4), but this will necessitate selective injections of contrast material into both the external and internal carotid arteries as well as both vertebral arteries and, occasionally, super-selective injections into the larger feeding arteries. DSA is also vital in the detection of anatomic variants, associated aneurysms, and normal vessels of passage (Fig. 21.2a, b).

**Fig. 21.3** MRI and MRA determine the precise location of the AVM in quadrigeminal cistern after DSA of posterior circulation

#### **21.2.1 Approach**

Posterior fossa AVMs are very prone to rupture, and treatment should be considered in every case, except perhaps for the elderly patients with incidental lesions. In AVM treatment, the aim is to eradicate the malformation completely without disrupting normal blood flow. Incomplete treatment provides no significant protection from further hemorrhage.

**Fig. 21.4** Right vertebral artery angiogram (DSA) demonstrates suboccipital AVM, feeders from PICA, AICA, and SCA

The decision of whether to treat these lesions and the choice of the best treatment modality is difficult. A multidisciplinary team of neurosurgeons, neuroradiologists, and radiotherapists is needed when selecting the best management strategy for each individual patient.

In that process one must take many factors into consideration:

After the evaluation of all of these factors, the most suitable modality of treatment is chosen as single or combined therapy which directs to prevent future hemorrhage and resolve the related symptoms (Fig. 21.2a–c).

#### **21.3 Modalities of Treatment**

#### **21.3.1 Endovascular Techniques**

During the last two decades, endovascular techniques have become a therapeutic option in the management of the AVMs. Preoperative embolization aims to devascularize a large AVM with particulate material, mostly by using rapidly (butyl cyanoacrylate, Histoacryl) or more recently by using a slowly setting glue (ethylene vinyl alcohol copolymer, Onyx). Complete obliteration of an AVM by a rapid embolization alone is an uncommon situation and accounts for only about 10% of all our cases, but with a slow technique of Onyx injection, it can be obtained in up to 50% of the selected cases [15].

Until now, however, none of the embolic agents, which have been used to obliterate these lesions, provide total protection against recanalization, regrowing, and rebleeding. Therefore, we use embolization as combined therapy preoperatively to diminish intraoperative bleeding, making the surgery resemble more that of extrinsic tumor removal. Endovascular techniques can also be used to obliterate the feeders that arise from the deep which are usually difficult to reach or controlled with microsurgical techniques, but such vessel may also difficult to reach by microcatheters.

Many complications may follow the embolization procedures, like occlusion of the main draining vein with risk of AVM rupture during or after the procedure, occlusion of arteries in passage, or occlusion of major cerebral arteries. In some locations in the posterior fossa, preoperative embolization may form a hard mass which later can be difficult to dissect from the cranial nerve roots or brainstem. Also, if the preoperative embolization is performed poorly, the result might be of more harm during the surgery rather than benefit; the surgery could become even more difficult especially if they embolized more draining instead of the feeder.

Recently, we started to perform both the embolization and the microsurgical removal at the same day to avoid hemorrhage resulting from the hemodynamic changes inside the nidus, caused by partial embolization of the AVM.

#### **21.3.2 Radiotherapy**

Irradiation activates the swelling and degeneration of endothelial cells and perivascular tissue, which promote thrombosis and proliferative fibroblastic repair [1]. These changes in the abnormal vessel walls lead to occlusion of the shunt and finally obliteration of the AVM. The success of this technique depends on the delivery of ionizing radiation in a precise and focused manner to the malformation and avoiding exposure of the surrounding brain. Traditionally, the indication of radiosurgery has been a deep location or a location in eloquent brain that is associated with high surgical morbidity and mortality; such locations include the basal ganglia and brainstem.

The obliteration of AV shunt by radiosurgery takes between 1 and 3 years with a risk of recurrent hemorrhage during this period; actually the rate of recurrent bleeding is 2.98%/year/patient [16], and it seems that the occurrence is the same as if the lesion had been left untreated.

#### **21.3.3 Microsurgery**

Microsurgery is considered an ideal treatment for ruptured AVMs. It is, however, controversial in unruptured AVMs, even if radical eradication allows a complete cure of the lesion. ARUBA study found that conservative treatment of unruptured AVMs is superior to the interventional ones (microsurgery, endovascular, and radiosurgery) [17]. The study has nevertheless been criticized because of the short follow-up time, the low number of patients that does not allow subgrouping of the patients according to location or size of AVM, and most patients in the interventional arm being treated by radiosurgical methods.

Laakso et al. studied retrospectively 623 AVM patients [4]. The total follow-up is 10,165 personyears, and this study provides a significant longterm follow-up. In their study, they compare the survival of AVM patients to the general population. Their results show that AVMs are associated with significant and long-lasting excess mortality that is considerably lower in actively treated

decision-making regarding incidentally found unruptured AVMs is difficul [4, 5, 13, 18]. The decision of whether to operate on AVMs is based on many factors mentioned before. Size and location are the most important factors in the

patients. Even with these results, however, the

decision-making; major involvement of the brainstem may increase the risk above acceptable. We found superficial and vermian cerebellar AVMs generally favorable for microsurgical treatment. In ruptured AVMs, the hematoma cavity surrounding the nidus facilitates removal of even deep-seated lesions [5, 19].

Drake et al. in their series had no morbidity or mortality in small AVMs (<2.5 cm), and just over 15% morbidity and mortality in large AVMs (>5 cm) [1].

#### **21.4 Steps of the Surgery**

Posterior fossa AVMs are classified into (1) cerebellar hemispheric AVMs (tentorial, suboccipital, and petrosal); (2) vermian AVMs (suboccipital and tentorial); (3) tonsillar AVMs; and (4) brainstem AVMs (midbrain, pontine, and medulla oblongata) [1, 14].

In Helsinki we use four approaches to resect most posterior fossa AVMs: (1) supracerebellar approach for cerebellar tentorial, vermian tentorial, and posterior midbrain AVMs; (2) suboccipital approach for cerebellar suboccipital and vermian suboccipital AVMs; (3) suboccipital telovelar approach for tonsillar AVMs; and (4) retrosigmoid approach for cerebellar petrosal and some brainstem AVMs.

#### **21.4.1 Supracerebellar Approach** [20]

Unless contraindicated, e.g., due to old age and cardiac disease, we use the sitting position for the supracerebellar approach. The advantages of this approach are providing better drainage of CSF and possible less bleeding during surgery, provide a relax vein, and being able to observe the superior anatomical view of the AVM and identify the feeder. But we need to be careful with the risk of air embolism, cervical myelopathy, and hypotension.

Instead of the classical midline supracerebellar approach, we prefer paramedian approach. Its advantages are fewer veins in the surgical trajectory, less steep tentorium, and reduced risk of air embolism due to avoidance of exposure to the confluence of sinuses. The disadvantage is the difficulty to identify the best trajectory toward the center of the quadrigeminal cistern.

#### **<IP_ADDRESS> Positioning**

The sitting position we use in Helsinki is similar with praying position. We bent the upper torso and head of the patient forward about 30° and downward. By doing that, we expect the tentorium would be almost horizontal. This position will provide a good viewing angle from the most cranial portions of the posterior fossa to the lowest part. Two fingers have to fit between the chin and sternum; it will provide enough room to prevent compression of the airways and jugular veins.

#### **<IP_ADDRESS> Incision and Craniotomy**

We make a linear incision 2–3 cm lateral from the midline. The paramedian incision will start about 2 cm cranial to the occipital protuberance and extends until the craniocervical junction. The muscle can be easily split until the occipital bone, along the incision line, and can be held with selfretaining retractor. To spread the wound, we place a curved retractor both from cranial and caudal directions. We detach the muscle insertions with diathermia and expose the occipital bone. Bony exposure is usually enough at 3–4 cm below the transverse sinus.

We place one burr hole 3 cm lateral from the midline, slightly superior to the transverse sinus. We detach the dura from the transverse sinus, gently with blunt and curve dissector. Then we perform craniotomy with 3–4 cm bone flap. The bone flap should be above the transfer sinus to allow retraction of transfer sinus cranially. The bone opening should leave 1 cm edge of bone to the midline.

#### **<IP_ADDRESS> Dural Opening**

Sometimes the draining vein or the AVM itself is firmly adherent to the dura. Therefore, we carefully inspect the dura under the microscope to avoid any injury to the draining vein. To avoid injury to the veins or transverse sinus, the dura is opened under microscope. We open the dura in a V-shaped form and the base at the sinus. Many veins at supracerebellar area usually located in the midline such as superior cerebellar vein and could be avoided with this approach. Once the thick arachnoid and few of the bridging veins between tentorium and cerebellum were coagulated and cut, the cerebellum will follow the gravity, allowing a good surgical view without any brain retraction.

#### **21.4.2 Retrosigmoid Approach** [20]

This approach is described in detail elsewhere in this book. We describe only our modification of this technique.

#### **<IP_ADDRESS> Positioning**

We place the patient in lateral position (park bench), with the head elevated about 20 cm above the heart level. We rotate the upper body slightly (5–10°) backwards, in order that the shoulder is retracted with tape more easily caudally and posteriorly. The head (1) is slightly flexed forward, (2) may be tilted laterally, and (3), if necessary, may be rotated slightly toward the floor.

To gain slack brain, we use spinal drainage with 50–100 ml CSF removed.

#### **<IP_ADDRESS> Skin Incision and Craniotomy**

We place a linear incision 2 cm behind the mastoid process. The length of incision varies depending on distance of the AVM from the foramen magnum. Of importance is to have the skin incision long enough to obtain an adequate bony exposure. We place a large-sized curved retractor at the cranial side of incision. We continue to split the subcutaneous fat and muscles with monopolar until we found the yellowish fat at the level of the foramen magnum. This should be a sign for warning of extracranial vertebral artery.

We made one burr hole just at posterior border of the incision and then continue with the craniotomy. A bone flap of 2–3 cm is usually sufficient. If necessary, the bony opening can be extended by drilling mastoid part of the temporal bone. If the mastoid air cells are exposed, they really need to be meticulously closed to prevent the postoperative CSF leak.

#### **<IP_ADDRESS> Dural Opening**

The duramater is opened in a curvilinear shape, and the base at the mastoid. The dura edges are tackled with sutures. When the dura cut near the transverse sigmoid junction, the dura will be cut in a three-leaf fashion. One is directed exactly to the junction for better exposure.

The brain should be slack due to the spinal drainage, and once the dura is opened completely, we may close the drain temporarily. If the brain is still tight, opening the cerebellomedullary cistern (cisterna magna) helps to slack the brain. In this approach, the petrosal vein is often the prominent vein seen when approaching the tentorium or the upper cranial nerves. Although some papers mention that we may sacrifice this vein, many surgeons have observed complications after its occlusion. The best suggestion is to preserve it.

#### **21.4.3 Suboccipital Craniotomy** [20]

#### **<IP_ADDRESS> Positioning**

We usually use the sitting position described previously in this chapter.

#### **<IP_ADDRESS> Incision and Craniotomy**

We make the incision on the midline. The incision starts from the external occipital protuberance and extends till the C1–C2 level. We split the muscles at the midline with monopolar all the way to the occipital bone. If we split it exactly at the midline, there will be less vascular tissue. We place one large self-retaining retractor on each end, cranial and caudal. When dissecting the muscles, care is needed to avoid injury to the vertebral artery, which is located 1–2 cm from the midline.

We place one burr hole 1 cm paramedian from the midline, below the transverse sinus. We make two cuts with the craniotomy toward the foramen magnum. At the cranial aspect, the bone flap is secured with strong and large rongeur. If needed, we use a high-speed coarse diamond drill or a small rongeur to extend the lateral exposure of the foramen magnum.

#### **<IP_ADDRESS> Dural Opening**

We open the dura under a microscope in a reverse V-shaped form, and the base at the foramen magnum. We start dura cutting below the occipital sinus, and the dural leaf is everted caudally and sutured tightly to the muscles. At this point, usually the arachnoid membrane that covers cisterna magna is usually intact. The arachnoid is opened and attached it to dural leaf using hemoclips. Then under high magnification, we gently push apart the cerebellar tonsils, and we start to enter the fourth ventricle. By changing the table and microscope angle, we may even obtain visualization of superior part of fourth ventricle and aqueduct.

#### **<IP_ADDRESS> Dissection**

Mostly microsurgical removal of AVMs is a great challenge. In posterior fossa AVMs, the lesion is located deep in a small compartment close to many critical structures, which makes posterior fossa AVM surgery even more difficult. Therefore, only experienced neurovascular team should operate on these lesions (Table 21.2).

After opening the dura, we inspect the AVM under less magnification to estimate the nidus and their relationships to the adjacent neurovascular structures. We discern also the superficial feeders, the pattern of draining veins, and the plane of cleavage. During this initial inspection of the AVM, we use indocyanine green (ICG) angiography to distinguish arterial feeders from arterialized draining veins. ICG provides great help in this purpose.

We perform all the AVM dissection using maximize magnification. The cleavage plane between the nidus and the neural tissue is distinguished as a yellow gliotic tissue formed by previous hemorrhage(s). The feeders enter the AVM through this plane, and they should be identified, coagulated, and cut at this point. If no clear plane surrounds the AVM, especially in critical areas, dissection must be considered on the AVM itself depending on the axiom that no normal neural tissue between the AVM aggregation.

Besides carefully studying of 3D reconstruction images preoperatively, the large superficial feeding arteries are identified intraoperatively with ICG. We often place temporary clips only on the feeders that terminate in the AVM and avoid the main trunk of en-passage arteries, which also have branches that supply the normal cerebellum and/or

**Table 21.2** Characteristics of 64 patients with infratentorial arteriovenous malformation, stratified by result of treatment [4]

brainstem. Unintended occlusion of these branches may cause devastating brainstem infarction.

The small feeders should be coagulated directly in the cleavage plane. The tiny and fragile feeders, or dilated capillaries around the AVM, remain the most difficult part of the procedure, particularly when these vessels are close to the ventricle. Because of their fragile nature and little tissue to act on, bleeding from these tiny vessels is difficult to control. We use continuous coagulation with nonsticking bipolar forceps, which we quickly interchange when they become soiled. Bipolar is also used to shrink the AVM and to clarify the cleavage plane.

After disconnecting all the feeders, the AVM becomes border-free, bloodless, smaller, and non-tense, and the color of the draining vein(s) changes from red into blue. At this point, the draining vein can be coagulated and divided safely. If the venous drainage is obstructed during the procedure prior to this point, the AVM may become tense and prone to massive uncontrolled bleeding, and also swelling of the cerebellum can occur. If a secondary draining vein impedes the resection, the trick is to occlude this vein by a temporary clip. If no swelling of the AVM or cerebellum is observed, dividing the vein is safe.

Once the total AVM removal is achieved, the cavity should be carefully inspected for any remnants. Our technique is to touch all walls with the cotton and bipolar tip gently. A bleeding may indicate an AVM remnant, and another resection plane should be performed in that location. Hemostasis of the resection cavity must be meticulous. We use hemostatic materials (Tachosil ®, Surgicel ®, fibrin glue) to seal the resection cavity.

The dura should be closed in watertight and few stitches are used to lift it up to the bone edges. We put back the bone flap and secure it before closing the wound in layers.

#### **21.5 Expert Opinion and Suggestions to Avoid Complications**

**Fig. 21.5** Post-op vertebral artery angiogram demonstrates complete surgical removal of the AVM

#### **21.6 Postoperative Care and Follow-Up**

At the end of the procedure, immediate CT and CT angiography are performed directly before awaking the patient to check any postoperative hematoma and to find out any remnant in the AVM resection bed; then the patient is transferred to the neurosurgical ICU, where ECG, arterial blood pressure, central venous pressure, and other vital signs are recorded. Patients with small AVMs are woken up slowly over the period of several hours; those with large or complex AVMs are kept sedated and under moderate hypotension (mean arterial pressure 20% below the patient's normal level) by restricting fluid intake and hypotensive medications for several days. Careful repeat neurosurgical assessments are achieved.

Postoperative DSA is used to check if the AVM is completely eradicated.

#### **Conclusion**

Posterior fossa AVMs are very prone to rupture, and their treatment should be considered in almost every case. Microsurgical removal of posterior fossa AVMs is a big challenge in neurosurgical practice. Therefore, only experienced neurovascular team should operate on these lesions. The decision of whether to treat these lesions and choosing the best treatment modality is complex. A multidisciplinary team of neurosurgeons, neuroradiologists, and radiotherapists is important in the selection of the best management in each individual patient.

#### **References**

**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

**22**

## **Endovascular Coiling of Intracranial Aneurysms**

Naoya Kuwayama

#### **22.1 Introduction**

Since the development of Guglielmi detachable coil (GDC), endovascular technique for coiling has become widely accepted as one of the option treatments of intracranial aneurysms.

The randomized trial of ISAT [1] proved the superiority of the aneurysm coiling than clipping for the patients with subarachnoid hemorrhage. Endovascular aneurysm treatment has been rapidly developing in technique, and its indication has been also rapidly spreading with the development of a variety of adjunctive techniques, including simple coiling, catheter- or microwireassisted coiling, double-catheter technique, balloon remodeling technique, and stent-assisted technique. In this educational chapter, the standard and most updated coiling techniques will be explained including advantages and drawbacks. The flow diverters will not be mentioned here.

#### **22.1.1 Antiplatelet Therapy**

Antiplatelet agents (aspirin and/or clopidogrel) should be given to the patients with unruptured aneurysms, 1 or 2 weeks before the treatment, to

N. Kuwayama

Division of Neuroendovascular Therapy, Department of Neurosurgery, University of Toyama, Toyama, Japan e-mail<EMAIL_ADDRESS>
prevent thromboembolic complications. When using a simple technique, a single agent (aspirin or clopidogrel) will be enough, while when using the adjunctive techniques, dual antiplatelet therapy (DAPT) will be recommended. If using the stents, DAPT is mandatory and should be kept within several months after the treatment. However, we should be aware of the hemorrhagic complications due to the DAPT medication (Match Study) [2]. In cases with ruptured aneurysms, single agent will be given after procedure or during treatment through the nasogastric tube. When using stents, loading dose of aspirin (300 mg) and clopidogrel (300–600 mg) should be given during or immediately after procedure. Increase of blood aspirin level is rapid but that of clopidogrel is slow, taking several hours even if the loading dose is given.

"VerifyNow (Accumetrics)" is an easy, instant, and portable instrument to assess the platelet aggregation activity of the patient immediately before treatment. The degree of suppression of platelet activity with either aspirin (ARU) or clopidogrel (PRU) can be monitored.

#### **22.1.2 Anesthesia**

Usually general anesthesia is favorable and selected to get immobilization of the patient particularly in case of ruptured aneurysms. If a patient would bleed in the procedure, vital sign

J. July, E. J. Wahjoepramono (eds.), *Neurovascular Surgery*, https://doi.org/10.1007/978-981-10-8950-3\_22

could be controlled much better under intubated condition. Local anesthesia could be selected if the patient could well understand and stay still, but not recommended.

#### **22.1.3 Heparin**

Usually femoral arteries are selected for the access routes. After puncture of the artery, heparin should be given to maintain the ACT (activating clotting time) at 1.5–2 times of pretreatment level. We usually give 3000– 5000 units in bolus intravenously at first and then 1000 units every 1 h.

#### **22.1.4 Procedures of Coiling**

Though the simple technique should be the best, we have to utilize many kinds of adjunctive techniques to protect the parent artery from coil herniation out of the aneurysm dome. The practical techniques with microguidewires, microcatheters, balloons, and stents will be explained.

#### **22.2 Simple Coiling, Basic Techniques, and Follow-Up**

A 6Fr guiding catheter is usually selected to prepare for the second microcatheter usage. The first microcatheter is used for coiling and the second microcatheter (balloon catheter) is used for the adjuctive techniques. A microcatheter should be inserted into the aneurysm dome using a microguidewire. The detachable platinum coils are conceptionally divided into three types: framing, filling, and finishing coils. The decision to choose the size of framing coil should be same with or 0.5–1 mm smaller than the aneurysm diameter. When the aneurysm is spherical shaped, the size of framing coil should be the medium diameter between the long and short axes. The filling coils, shorter and smaller, come next and pack inside the framing coil. Then a few finishing coils follow and finalize the treatment. The finishing coil should be much softer and shorter. Final stage, the microguidewiere should be proceeded into the tip of the microcatheter and pulled back together securing the inside coils not coming with the catheter. The optimum packing rate will be 20–25% or more, and it is reported that the higher the packing rate, the less the recurrence rate [3].

The follow-up should be done under the monitor of plain craniogram and MRI time of flight (TOF) sequence. Morphological changes of the coil in the craniogram and/or inside flow into the aneurysm dome in MRI-TOF images will indicate the recurrence of the aneurysms. Then the angiogram should be done to evaluate the necessity of retreatment.

#### **22.3 Adjunctive Techniques**

A 6 or 7 Fr guiding catheter is usually selected to go with two or three catheters in combination. Sometimes a balloon-guiding catheter (7 or 8 Fr) is used to stabilize the intracranial remodeling balloon catheter or to control intraoperative bleeding. Here, five kinds of adjunctive techniques will be shown.

#### **22.3.1 # Wire Protection Method**  (Fig. 22.1)

This is suitable to a small aneurysm arising from a small parent artery. Place a microguidewire passing across the aneurysm neck in the parent artery. It is sometimes useful to prevent the coil from protruding out of the aneurysm neck.

Figure 22.1 shows the anterior communicating artery (AcomA) aneurysm. The microguidewire is coming through the left internal carotid artery (ICA) and going to the distal right A2 segment through the AcomA, while the microcatheter is coming from the right ICA and inserted into the aneurysm dome. The coils do not come out of the dome with the protection of the microguidewire across the aneurysm neck.

**Fig. 22.1** The wire-assisted technique for an aneurysm of the anterior communicating artery

#### **22.3.2 # Catheter Protection Method**  (Fig. 22.2)

This is a modified method of the wire protection procedure. Place a microcatheter passing across the aneurysm neck in the parent artery. This is available in the small vessel like anterior cerebral arteries and in the posterior circulation.

Figure 22.2 demonstrates the aneurysm of the left VA-PICA. The microcatheter is coming from the contralateral right vertebral artery and going to the left PICA into its distal segment, while the second microcatheter is coming from the left vertebral artery and going into the aneurysm dome.

#### **22.3.3 # Double-Catheter Method**  (Fig. 22.3)

In case with wide-neck aneurysms, coils are easily herniated from the dome. Sometimes a loop of a detached framing coil may come out of the dome, being pushed by filling coils. In these cases, the double-catheter technique is often useful. First, send the two microcatheters into the aneurysm dome. Then start coiling. When the first coil makes a good frame in the dome, keep the coil undetached and push and hold the catheter slightly pressing the framing coil to the dome side. Then start filling inside the frame with the second catheter. Usually after detaching two or three filling coils inside the dome, the framing coil will be stabilized well and not be herniated to the parent artery. Then the framing coil can be detached. Afterward, both the first and the second catheters can be used for the coil insertion depending on the situation.

Figure 22.3 shows the recurred aneurysm at the right posterior communicating artery (PcomA) after clipping. The previous multiple clips caused the tight stenosis of the ICA proximal to the aneurysm, allowing just one microcatheter to pass through the stenosis. While placing a microcatheter from the right ICA, the second microcatheter was coming from the contralateral left ICA through the AcomA, going down to the right ICA, and finally placed in the aneurysm dome. Thus, the wide-neck aneurysm was completely packed with the double-catheter technique.

#### **22.3.4 # Balloon Remodeling Method**  (Fig. 22.4)

First, send the balloon catheter to the distal parent artery and then send the microcatheter into

recurrent aneurysm of the right ICA after clipping. The previous clips make the tight ICA stenosis and only one catheter can pass through the ICA. The 2nd catheter is navigated from the left ICA throught AcomA.

Left: 1st microcatheter going from the right ICA to the aneurysm dome. Middle: 2nd microcatheter going from contralateral ICA to the aneurysm through the AcomA. Right: abgiogram after coiling.

**Fig. 22.3** The double-catheter technique for a recurrent wide-neck aneurysm of the right ICA after clipping

**Fig. 22.4** The balloon remodeling technique for an aneurysm of the posterior communicating artery (PcomA). The aneurysm arises from the PcomA. This is the socalled pure Pcom aneurysm (left). The aneurysm is being

the aneurysm dome. The movement of one catheter will affect the position of the other catheter by the friction of both catheters. Surgeon should always be aware of the position of the tip of coil catheter, when moving the microballoon catheter, otherwise it may cause perforation of the aneurysm. When the balloon and microcatheter are placed properly, start coiling. The balloon can be inflated, if necessary, to prevent the coil coming out of the dome. Surgeon must remember that the inflated balloon will fix the tip of the coil catheter and prevent its free movement, causing rupture of the aneurysm. The balloon should be inflated under road mapping up to the size of the parent artery, not to cause the vessel rupture.

Figure 22.4 shows the so-called pure PcomA aneurysm (arising from PcomA itself). In the final stage of the procedure, the balloon was inflated in the PcomA preventing the finishing coils from herniating to the parent PcomA.

packed with balloon remodeling technique (middle). The balloon is inflated in the parent PcomA to prevent coil herniation. The aneurysm is completely obliterated with coils keeping the PcomA patent (right)

#### **22.3.5 # Stent-Assisted Technique**  (Fig. 22.5)

There are several kinds of remodeling stents: open cell type, closed cell type, braided type, etc. To use the stents, DAPT medication before procedure is mandatory to prevent thromboembolic complication. There are two ways to send the coil catheter to the aneurysm: one is jailing technique and the other is trans-cell technique. In case of jailing technique, send the stent catheter to the distal parent artery. Before opening the stent, send the coil catheter into the aneurysm dome. Then open and deploy the stent, and start coiling. In case of trans-cell technique, send the stent catheter to the distal parent artery and then open and deploy the stent. Send the coil catheter to the aneurysm through the cell of the stent, and start coiling. The demerit of the trans-cell method is to have a potential risk of wire or catheter perforation in cases with small aneurysms.

**Fig. 22.5** The stent-assisted technique for an aneurysm of the origin of the superior cerebellar artery. (**a**) The aneurysm arises from the origin of the superior cerebellar artery (BA-SCA AN) (**b**) The aneurysm is being packed with balloon-assisted technique at first. The balloon is

At present, the jailing method seems to be dominantly used. The demerit of the jailing method is to fix the coil catheter preventing the free movement of the tip of the microcatheter. Recently semi-jailing method is frequently used, keeping the stent half open at the neck to secure the free movement of the coil catheter. In other words, the semi-jailing method makes the neck of the aneurysm smaller, allowing free catheter movement and easy and safe coiling. It is reported that stent-assisted coiling has smaller rate of recurrence due to the hemodynamic effect to the aneurysm [4].

Figure 22.5 demonstrates a case with the aneurysm of the superior cerebellar artery treated with balloon- and stent-assisted technique. Coiling started with balloon-assisted technique; then finally the stent (Elvis Jr.) was deployed from the PCA-P1 segment to the basilar artery.

inflated from the right PCA-P1 segment to the upper basilar artery. (**c**) The aneurysm is completely obliterated with balloon- and stent-assisted technique. (**d**) Note the stent (arrows) is placed from the left PCA-P1 segment to the upper basilar artery

#### **References**

**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

**23**

## **Transparent Sheath for Neuroendoscopic Intracerebral Hematoma Surgery**

Daisuke Suyama, Jun Hiramoto, Kei Yamashiro, Yasuhiro Yamada, Tsukasa Kawase, and Yoko Kato

#### **23.1 Introduction**

Neuroendoscopic procedures for spontaneous cerebral hemorrhage have recently increased. This is a result of the reports published by Nishihara et al. in 2000 [1], describing how to use the neuroendoscopic to evacuate the intracerebral hematoma by using a transparent sheath. Following this, 300 surgical cases of spontaneous intracerebral hemorrhage have been performed with an endoscope in our institution, and in related facilities, between 2000 and 2015. This procedure is commonly performed with only one or two burr holes under local anesthesia. If the

Department of Neurosurgery, Fujita Health University, Banbuntane Hotokukai Hospital, Nagoya city, Aichi, Japan e-mail<EMAIL_ADDRESS>
J. Hiramoto Department of Neurosurgery, Fuchu Keijinkai Hospital, Tokyo, Japan

K. Yamashiro · Y. Yamada · T. Kawase Department of Neurosurgery, Fujita Health University, Banbuntane Hotokukai Hospital, Nagoya city, Aichi, Japan e-mail<EMAIL_ADDRESS>
Department of Neurosurgery, Fujita Health University, Toyoake, Aichi, Japan e-mail<EMAIL_ADDRESS>
transparent sheaths are introduced into hematoma safely, endoscopic procedures will be successful in any location of spontaneous hematomas.

#### **23.2 Preoperative Preparation**

Prior to the surgery, if the hematoma is at unusual location, the patient needs an angiography or at least three-dimensional computerized tomographic angiography (3D-CTA) or magnetic resonance angiography (MRA) to rule out the possibility of vascular malformation, such as arteriovenous malformation (AVM), aneurysm, or dural AV fistula.

To decide on surgical approach, 3D-CT was performed with scalp marker. For deep-seated hematoma like thalamic hemorrhage, we used stereotaxic system or navigation system in order to insert transparent sheath.

#### **23.2.1 Surgical Tools**

For this surgery, we use endoscope, suction tube, and transparent sheath. There are several different types of transparent sheath depending on the case. Some cases require small diameter of 5 mm, but some require 10 mm. Soft blood clot may need small suction of 2 mm, but hard clot may need bigger one such as 4 mm. Rigid and flexible

D. Suyama (\*)

Department of Neurosurgery, Fuchu Keijinkai Hospital, Tokyo, Japan

Y. Kato

**Fig. 23.1** Surgical tools for endoscopic evacuation of intracerebral hematoma

endoscopes are available and their diameter is 2.7 and 4.8 mm (Fig. 23.1).

#### **23.3 Steps of the Surgery**

#### **23.3.1 Burr Hole and Hematoma Evacuation**