A total of 81 spinal arachnoid cyst patients (male:female 34:47, mean age 32 years) undergoing surgery in Beijing Tiantan Hospital from January 1995 to December 2010 were retrospectively studied. The study protocol was approved by the Ethics Committee of Beijing Tiantan Hospital. Written informed consent was obtained from all patients or from guardians for patients less than 18 years old.
Inclusion criteria were: 1) diagnosis of idiopathic or congenital spinal arachnoid cyst based on MRI and clinical features, using the diagnostic criteria provided by Hughes et al; 2) aged 6-70 years at the time of treatment; and 3) conservative-treatment failure, and patient still exhibiting a baseline preoperative Fugl-Meyer (FM) score of <50 after conservative treatment. Exclusion criteria were: 1) diagnosis of another disease requiring clinical intervention or impairing routine operative care, including spinal tuberculosis or tumor; 2) undergoing treatment for diabetes mellitus or other chronic diseases; or 3) had been diagnosed with arachnoid cysts secondary to trauma, including hemorrhage, inflammation, surgery, or lumbar puncture.
All patients underwent routine MRI examinations. Spinal arachnoid cysts were identified based on apparent low-signal regions in T1-weighted images. Similarly, high signals were used to indicate cerebrospinal fluid without enhancement in T2-weighted images. All examinations were conducted in accordance with previously published guidelines.
Both anatomical location and abnormalities observed by MRI were assessed for each patient. Surgical procedure of spinal arachnoid cysts was determined before the year 1995 in our department. Spinal arachnoid cysts were subdivided into five types: 1) intramedullary cysts/syrinxes, 2) subdural extramedullary, 3) subdural/epidural, 4) intraspinal epidural, or 5) intraspinal/extraspinal (Figure 1). If surgical observation was inconsistent with preoperative evaluation by MRI, the surgical procedure was modified according to intraoperative observations.
Surgical treatment was selected based on spinal arachnoid cyst type and conducted by a team of two trained surgeons and two assistants. All surgeries were conducted at the same facility. The use of total or partial resection was recorded for each patient.
For patients with this kind of cyst, experimental puncture was performed to identify the location of the cysts, then an incision along the posterior median sulcus was made to achieve cyst opening (the length of the incision varied according to the size of the cyst). For some patients with dense adhesion between the cyst wall and spinal cord, the separation of the cyst was not continued if it was very difficult to separate. On the contrary, the clinicians removed the parts that could be separated or sutured the pia mater to the cyst wall and ensured the connection of the cyst cavity and the subarachnoid space to prevent the recurrence of the cyst.
Subdural extramedullary spinal arachnoid cysts feature abnormal thickening and adhesion of the arachnoid caused by congenital aplasia and/or inflammatory responses. These abnormalities are commonly found at the ventral and ventrolateral spinal cord. Posterior shifting of the spinal cord is generally found in patients with cysts at the ventral and ventrolateral spinal cord, and thickening and adhesion of the arachnoid that could lead to dense adhesion between the spinal cord and the endorrhachis. Thus the incision of the endorrhachis should be carefully performed with the assistance of endoscopy to avoid injuries to the spinal cord. The long-term pressure on the spinal cord could result in the adhesion and thickening of the adjacent arachnoid and poor spinal cord pulsation. Thus the adhesive arachnoid between the spinal cord and the adjacent endorrhachis was separated carefully and removed as much as possible to release the spinal cord. However, the operational view of the surgical procedures on the cysts at the ventral spinal cord is generally limited, and traction of the spinal cord should be avoided as much as possible to avoid damage to the spinal cord nerves and adjacent vessels.
Subdural/epidural cysts were treated by resection of the cyst wall. If no dense adhesion between the cyst wall and the endorrhachis or nerve root was found, the cyst was separated until the neck of the cyst, and then tight suturing was performed after resection of the cyst. In contrast, if dense adhesion between the cyst wall and nerve root made the separation of the cyst very difficult, partial removal of the cyst was performed, and then tight suturing was performed after the connecting hole had been filled with a section of free muscle mass. For cysts not connected with the subarachnoid space, the cyst wall was removed as much as possible. In cases of dense adhesion between nerve root and the cyst, the cyst wall was partially resected for drainage and decompression before tight overlapping suturing. A section of free muscle mass was then positioned on the dura at the site of the cyst and fixed by suture and inward pressure to prevent new cyst formation.
Intraspinal epidural cysts were treated by ligation of the cervix. In some cases, the muscle mass was isolated and used to plug the access hole prior to suturing of the cyst walls. If the nerve root or dural adhesion was weak, the cyst was mobilized to the neck, resected, and sutured tightly. However, in cases of very strong nerve root or dural adhesion the cyst wall was partially resected and a piece of free muscle mass was used to plug the access hole prior to tight suturing.
Intraspinal and extraspinal cysts were removed through enlarged intervertebral foramina. Extraspinal cysts are easy to be treated. Operation of intraspinal cysts is similar to subdural/epidural cysts. If no dense adhesion between the cyst wall and the endorrhachis or nerve root was found, the cyst was separated until the neck of the cyst, and then tight suturing was performed after resection of the cyst. If dense adhesion between the cyst wall and nerve root made the separation of the cyst difficult, partial removal of the cyst was performed, and then tight suturing was performed with a section of free muscle mass. For cysts not connected with the subarachnoid space, the cyst wall was removed.
All patients were followed up, with a mean period of 69 months (range 3-187 months). Cases of recurrence, death, or second surgery were recorded.
FM scores were assessed preoperatively and at postoperative day 90 on a 0- to 99-point scale. As previously described, FM scores were assessed as severe or marked motor impairment (0-84), moderate motor impairment (85-95 points), and slight motor impairment (96-99 points).
Preoperative FM scores of all patients were less than 50 points after conservative therapy. Significant improvement was determined when postoperative FM score achieved 96-99, and clinical symptoms disappeared with incident pain or numbness; patients had a normal life and work. Improvement was determined when postoperative FM score achieved 85-95, and parts of symptoms disappeared but some moderate motor impairment still remained. No improvement was determined when postoperative FM score remained 0-84.