laminectomy without reconstruction has been the standard surgical treatment method for intradural and posterior epidural spinal lesions7 ) .
although this surgical technique provides an adequate operative field , it may lead to hematoma in the spinal canal , invasion of scar tissue after surgery , or postoperative instability and scoliosis45 ) . as microscopic surgical techniques have evolved ,
new surgical methods such as laminoplasty with the use of a t - saw for reconstruction36 ) or laminoplasty with a 90 or 60 change in the lamina with en bloc removal14 ) have been introduced .
some authors have reported that certain spinal cord tumors can be removed through hemilaminectomy and a minimally invasive technique that involves the use of a tubular retractor system , which enables maximum preservation of the posterior elements210 ) . here ,
we report a spinous process - splitting hemilaminoplasty technique that maintains the shape and integrity of the posterior elements and retains a barrier that prevents hematoma in the spinal canal and scar tissue damage .
between 2011 and 2014 , spinous process - splitting hemilaminoplasty was performed in nine patients .
physical examinations , mri with gadolinium , ct , and routine radiography with dynamic imaging of the intradural and posterior epidural lesions were performed prior to surgery .
unilateral paravertebral muscle dissection reveals the lamina and a part of the medial facet joint .
a hole is created in the spinous process , lamina , and medial articular facet with a match head burr ( 1.7 mm ) drill to achieve laminoplasty to replace the bone that was removed en bloc into the exact pre - surgery position .
the splitting of the spinous process can be performed by 1 ) cutting to a depth determined on the basis of measurements on computed tomography ( ct ) scans with an oscillating saw in the midline where the epidural space is wide or 2 ) splitting with the t - saw by partially removing the surrounding ligament flavum to facilitate use of the t - saw , revealing the dura and enabling passage of the t - saw stylet . in the cases reported here
, we used both methods and found that the t - saw method resulted in less bone loss due to the cutting . using a fine burr ,
we linearly drilled the laminofacet junction into the spinal canal in order to perform the hemilaminectomy .
this approach secures a wider operating field than previous hemilaminectomy procedures , as the surgeon is able to see as much as half of the spinous process .
furthermore , undercutting of the opposite side of the spinolamina junction enables the surgeon to see the dura margin on the contralateral side , providing enough space to treat intradural and posterior epidural lesions .
finally , the 1-cm operating field is wide enough to place dura sutures . after removing the spinal lesion
, we performed suture for the spinous process and the laminofacet junction , which enabled laminoplasty with similar pre - surgery integrity . of note , placing the sutures on the split spinous process results in a stable suture on the laminofacet junction without subsequent movement .
non - absorbable suture threads were used to stabilize the surgical area and to prevent the formation of artifacts .
this is beneficial given that imaging techniques such as magnetic resonance imaging ( mri ) are used for follow - up inspection .
surgical outcomes were evaluated on the basis of postoperative symptom states and complications , operation time , and estimated blood loss ( ebl ) ( table 2 ) .
between 2011 and 2014 , spinous process - splitting hemilaminoplasty was performed in nine patients .
physical examinations , mri with gadolinium , ct , and routine radiography with dynamic imaging of the intradural and posterior epidural lesions were performed prior to surgery .
unilateral paravertebral muscle dissection reveals the lamina and a part of the medial facet joint .
a hole is created in the spinous process , lamina , and medial articular facet with a match head burr ( 1.7 mm ) drill to achieve laminoplasty to replace the bone that was removed en bloc into the exact pre - surgery position .
the splitting of the spinous process can be performed by 1 ) cutting to a depth determined on the basis of measurements on computed tomography ( ct ) scans with an oscillating saw in the midline where the epidural space is wide or 2 ) splitting with the t - saw by partially removing the surrounding ligament flavum to facilitate use of the t - saw , revealing the dura and enabling passage of the t - saw stylet . in the cases reported here , we used both methods and found that the t - saw method resulted in less bone loss due to the cutting . using a fine burr , we linearly drilled the laminofacet junction into the spinal canal in order to perform the hemilaminectomy .
this approach secures a wider operating field than previous hemilaminectomy procedures , as the surgeon is able to see as much as half of the spinous process .
furthermore , undercutting of the opposite side of the spinolamina junction enables the surgeon to see the dura margin on the contralateral side , providing enough space to treat intradural and posterior epidural lesions .
finally , the 1-cm operating field is wide enough to place dura sutures . after removing the spinal lesion
, we performed suture for the spinous process and the laminofacet junction , which enabled laminoplasty with similar pre - surgery integrity . of note , placing the sutures on the split spinous process results in a stable suture on the laminofacet junction without subsequent movement .
non - absorbable suture threads were used to stabilize the surgical area and to prevent the formation of artifacts .
this is beneficial given that imaging techniques such as magnetic resonance imaging ( mri ) are used for follow - up inspection .
surgical outcomes were evaluated on the basis of postoperative symptom states and complications , operation time , and estimated blood loss ( ebl ) ( table 2 ) .
the age of the patients ranged from 28 to 76 years ( mean , 60.2 years ) .
eight had an intradural extramedullary spinal tumor and one had ossification of the ligament flavum .
the surgical sites were cervical in six patients , thoracic in one , and lumbar in two ( table 1 ) .
spinous process - splitting hemilaminoplasty was performed on levels 1 - 3 with a mean operation time of 237.847.0 min ( range , 160 - 315 min ) and a mean ebl of 116.761.2 ml ( range , 50 - 200 ml ) .
post - surgical diagnoses were schwannoma in five patients , meningioma in two , neurofibroma in one , and ossification of the ligament flavum in one .
we performed total resection in the schwannoma , neurofibroma , and ossified ligament flavum cases , and simpson grade ii resection in the patients with meningioma ( table 2 ) .
the postoperative follow - up period was 6 to 31 months , and all patients were able to walk 1 day after surgery .
ct scans were obtained for each patient 6 months after surgery , and the findings confirmed that laminoplasty was achieved on the bone fusion without displacement .
a 57-year - old female patient had pain and numbness in her left arm for 3 months .
cervical mri revealed an intradural extramedullary spinal tumor leaning toward the left at c3 - 4 - 5 ( fig .
we split the spinous process on the left side of c3 - 4 - 5 , drilled the facet lamina junction , and performed en bloc hemilaminectomy . after removing the tumor
, we placed the detached bone fragments in their original position using non - absorbable suture threads ( fig . 2c ) .
ct performed 6 months after surgery revealed that bone fusion had been achieved ( fig .
3a , b ) , and a spinous - splitting hemilaminectomy was performed . to achieve optimal vision , undercutting of the contralateral spinous process was performed , which enabled the surgeon to see both sides of the dura to the same extent ( fig .
a 62-year - old female patient had progressive pain and numbness in the right arm 3 months prior to her hospital visit .
mri revealed an intradural extramedullary spinal tumor on the right side of c5 - 6 ( fig .
spinous process - splitting hemilaminectomy was performed on the right side of c5 - 6 , and the tumor was removed .
laminoplasty was performed in the same position , using non - absorbable threads ( fig .
a 57-year - old female patient had pain and numbness in her left arm for 3 months .
cervical mri revealed an intradural extramedullary spinal tumor leaning toward the left at c3 - 4 - 5 ( fig .
we split the spinous process on the left side of c3 - 4 - 5 , drilled the facet lamina junction , and performed en bloc hemilaminectomy . after removing the tumor
, we placed the detached bone fragments in their original position using non - absorbable suture threads ( fig . 2c ) .
ct performed 6 months after surgery revealed that bone fusion had been achieved ( fig .
3a , b ) , and a spinous - splitting hemilaminectomy was performed . to achieve optimal vision , undercutting of the contralateral spinous process was performed , which enabled the surgeon to see both sides of the dura to the same extent ( fig .
a 62-year - old female patient had progressive pain and numbness in the right arm 3 months prior to her hospital visit .
mri revealed an intradural extramedullary spinal tumor on the right side of c5 - 6 ( fig .
spinous process - splitting hemilaminectomy was performed on the right side of c5 - 6 , and the tumor was removed .
laminoplasty was performed in the same position , using non - absorbable threads ( fig .
although laminectomy has previously been used to treat intradural lesions , the surgical outcomes have often been compromised by hematoma , scar tissue invasion , and/or postoperative instability . with
asazuma et al.1 ) performed 90 degree - rotation laminoplasty on spinal cord and cauda equina tumors in seven patients and reconstructed the vertebral arch .
the authors reported satisfactory operative exposure , a maintained range of motion , and an improved japanese orthopedic association score .
hida et al.4 ) introduced a 60 degree - rotation laminoplasty with titanium mini - plates .
of the eight patients who underwent surgery , six had an intradural tumor as well as ossification of the ligament flava and spontaneous spinal cord herniation .
this can only be conducted on the thoracic and lumbar spine where the spinous process is long , but not on the cervical spine where the spinous process is short .
therefore , these techniques can only be used to treat thoracic and lumbar lesions . furthermore , because bone fusion does not mirror the original state , this technique can not be considered true reconstructive laminoplasty .
in contrast , the method that we introduced here involves minimizing bone loss by cutting the spinous process with a t - saw or oscillating saw to obtain a wide epidural space , enabling preservation of the pre - surgical appearance .
this technique is not only applicable to the thoracic and lumbar spine regions , but also to cervical lesions .
in addition , because it does not involve the use of titanium mini - plates , there are no artifacts , and therefore , imaging evaluations are more accurate , especially in cases of tumors that could be recurrent .
hemilaminectomy has been introduced as a surgical treatment for intradural lesions using a unilateral approach28 ) .
it preserves the contralateral muscles and ligaments , which prevents secondary instability and scoliosis after laminectomy .
however , in hemilaminectomy , the lamina is removed via a unilateral approach , and thus , the operative field is restricted .
in contrast , our technique involves splitting the spinous process , thereby allowing the midline of the dura to be seen ( fig .
3 ) . undercutting of the spinous process enables the surgeon to see around the midline of the dura and dura margins , and therefore , both sides become visible .
hara et al.3 ) performed en bloc laminoplasty on 16 patients using a t - saw , and similar to the results obtained using our technique , the bone shape remained similar before and after surgery .
the authors reported that by cutting the spinous process around the surgical level and placing the sutures , they were able to preserve posterior supporting elements such as the supraspinous and infraspinous ligaments , preventing kyphotic deformity after laminoplasty .
however , our method involves a smaller incision because the spinous process around the surgical area is not removed .
moreover , the midline and contralateral posterior elements remain intact , and thus , the physiological integrity of the spinous ligament is maintained while postoperative kyphotic deformity is prevented .
it should also be noted that splitting the spinous process where there is a large amount of cancellous bone , rather than the laminofacet junction , results in better bone fusion .
spinous process - splitting hemilaminoplasty and other surgical methods were compared with respect to operative time and blood loss12348 ) .
the operation time for 60-degree rotation laminoplasty3 ) was 233.7563.46 min ( 170 - 380 ) and blood loss was 218.75176.33 ml ( 45 - 600 ) , while for 90-degree rotation laminoplasty1 ) , the operation time was 338.29144.35 min ( 205 - 445 ) and blood loss was 578.43176.33 ml ( 73 - 2038 ) . for heminlaminectomy8 ) , operative time was 246.6761.54 min ( 180 - 320 ) and blood loss during surgery was 55.8312.01 ml . for en - bloc laminoplasty3 ) , surgery time was 350.6381.20 min ( 242 - 485 ) and blood loss was 589.31282.89 ml ( 90 - 1209 ) .
these results are similar to those obtained using our surgical technique . and the minimal operative time and bleeding on our surgical method were similar for other surgical methods .
the majority of spinal tumors are either intradural extramedullary ( 40% ) or extradural ( 55% ) tumors , and the intradural lesions often lean toward one side8 ) . in our cases , during same period , we treated a total of 11 cases of spinal cord tumors .
except for two patients with intradural intramedullary tumors and one patient with previous posterior spine surgery , spinous process - splitting hemilaminoplasty was performed in all cases where conventional techniques were applicable .
our novel surgical technique has advantages over previous laminectomy , laminoplasty , and hemilaminectomy techniques .
primarily , this new procedure enables adequate visualization during surgery and prevents scar tissue invasion and hematoma .
moreover , it does not cause injury to the muscles and ligaments on the contralateral side of the lesion , and thus prevents postoperative instability and subluxation .
finally , it should be noted that no imaging artifacts are produced as a result of the surgery , and therefore , imaging evaluations related to tumor recurrence are more accurate .
spinous process - splitting hemilaminoplasty for intradural and posterior epidural lesions preserves the contralateral posterior elements and maintains stability compared to previous reconstructive laminoplasty techniques .
visualization is also improved compared to previous hemilaminectomy techniques , and laminoplasty following this procedure helps maintain physiological integrity .
 objectiveto describe a novel spinous process - splitting hemilaminoplasty technique for the surgical treatment of intradural and posterior epidural lesions that promotes physiological restoration.methodsthe spinous process was split , the area of the facet lamina junction was drilled , and en bloc hemilaminectomy was then performed . after removing intradural and posterior epidural lesions , we fitted the previously en bloc - removed bone to the pre - surgery same shape , and held it in place with non - absorbable sutures . 
 surgery was performed on 16 laminas from a total of nine patients between 2011 and 2014 . 
 bony union of the reconstructed lamina was assessed using computed tomography ( ct ) at 6 months after surgery.resultsspinous process - slitting hemilaminoplasty was performed for intradural extramedullary tumors in eight patients and for ossification of the ligament flavum in one patient . because we were able to visualize the margin of the ipsilateral and contralateral dura 
 , we were able to secure space for removal of the lesion and closure of the dura . 
 none of the cases showed spinal deformity or other complications . 
 bone fusion and maintenance of the spinal canal were found to be perfect on ct scans.conclusionthe spinous process - splitting hemilaminoplasty technique presented here was successful in creating sufficient space to remove intradural and posterior epidural lesions and to close the dura . 
 furthermore , we were able to maintain the physiological barrier and integrity after surgery because the posterior musculature and bone structures were restored . 
INTRODUCTION
MATERIALS AND METHODS
Patients
Surgical procedures
RESULTS
ILLUSTRATIVE CASE PRESENTATIONS
Case 1
Case 5
Case 7
DISCUSSION
CONCLUSION