The classification codified during the International Symposium on Lumbar Canal Stenosis (Canada, 1975) have been a source of confusion amongst the neurosurgical community. The present study was initiated to clearly define the concept of lumbar canal stenosis starting with a reexamination of the original usage of the term by Verbiest. Also introduced are surgical techniques for the relief of lumbar canal stenosis and for disc excision in pure lumbar disc herniation. In our clinic, the determination of the appropriate surgical procedure is based upon the following criteria : 1) Laminectomy ; when 3 or more vertebral bodies exhibit stenosis. 2) Partial Laminectomy ; when localized stenosis is present. 3) Discotomy ; in case of pure disc herniation. 4) Full/Partial Laminectomy+Discotomy; canal stenosis with herniation. 5) Foraminotomy (unroofing of the lateral recess); superior facet syndrome.

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From November 1988 to January 1996, 38 cases with cranio-cervical lesions were treated surgically. The primary disease included 12 cases of rheumatoid arthritis, 7 cases of metastatic tumor of the spine, 5 cases of Klippel-Feil syndrome, 3 cases of cranio-cervical instability with Down syndrome, 2 cases of primary spinal tumor, 3 cases of pseudarthrosis after fracture of the axis, one case with odontoid fracture, one case with multiple myeloma, one case of post-laminectomy kyphosis after excition of spinal cord tumor, and one case with atlantoaxial instability with kyphotic deformity of unknown origin, atlantoaxial instability with athetoid cerebral palsy and cervical spondylosis, and one case of destructive spondyloarthropathy after long-term dialyses. Surgical methods included transoral anterior decompression in two cases, posterior occipito-cervical fusion using segmental spinal instrumentation in 32 cases, and a combination of both procedures in 4 cases. When the symptom of atlantoaxial instability or cranio-cervical instability was presented, posterior atlantoaxial fusion or occipito-cervical fusion was the treatment of choice. In most of the cases, reduction of the abnormal position of the bony structures was attempted after preoperative application of a Halo-vest with local anesthesia. Reduction while the patient was in a state of consciousness, was not only safe and effective but also brought about temporalily the desired postoperative situation of decompression and stabilization for the patients. It was also an easier and less worrying procedure for the surgeons. Vertical subluxation was reduced effectively, thus deleting the necessity of transoral anterior decompression in many cases. Rigid and consistent stabilization was facilitated with the use of a sufficient amount of bone graft and instrumentation. This procedure is also applicable either as a primary procedure or as a secondary procedure when stabilization through the transoral approach is difficult. On the other hand, the transoral approach provides an excellent exposure of the compressive lesion in front of the spinal cord, facilitating decompression and offers histological specimens in diagnostically challenging conditions. Surgical complications were minimal. These procedures are safe and effective, if the surgeons are familiar with the indications for anterior and posterior approach operations.

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Surgical treatments of craniovertebral junction lesions, focused upon Atlantoaxial dislocation (AAD) and basilar impression (BI) are discussed according to our surgical indications and surgical methods. The total number of our surgical cases of atlantoaxial dislocation (AAD) and basilar impression (BI) are 96 (posterior fusion 63, transoral anterior approach 30, combinded approach 3). The surgical approach for each case was decided as follows : If AAD is reducible, posterior fusion is selected. In nonreducible AAD or BI, if the clivoaxial angle is under 120 degree, the transoral approach is selected and if the angle is over 120 degree, posterior decompression and fusion is selected. In posterior fusion, grafting bone taken from iliac crest has been used for posterior fusion, and recently titanian wire or titanian loop and other newly developed surgical instrumentation and materials are used. Except for 3 cases in which grafted bones were absorbed, recovery after surgery was satisfactory in 63 cases in which posterior fusion was used. Except for one case, neurological improvement was obtained in 30 cases using the anterior approach. In 3 cases in which transoral approaches were used. grafted bones slipped out of portion, but this did not result in neurological deterioration. The appropriate surgical approach selsected by considering the aspect of the compression to the neural tissue of the craniovertebral junction is as follows : Posterior approach when there is reducible AAD without anterior compression. Anterior approach when there is noreducible AAD with anterior compression or basilar impression.

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One-stage surgery, transoral anterior decompression and posterior fixation, were performed in 14 cases of irreducible atlantoaxial dislocation (AAD) with anterior cord compression. There were 4 males and 10 females with average age being 52 years and 6 months, and with 3 year follow-ups. Dynamic X-ray and tomography, magnetic resonance imaging and computed tomography were essential in diagnosis of irreducibility and anterior cord compression in AAD which were important conditions for selecting one-stage surgery. As to the positioning of patients in the operating room, supine-prone position was used in 7 and lateral rotatory position in 7. The operative method of posterior fusion has greatly changed over the years and various instruments have recently been used. Transarticular screw fixation in addition to midline bony fusion can be applied to cases with severe degree of AAD or marked instability, however, precise preoperative evaluation for high riding transverse foramen and intraoperative navigation system are recommended in order to avoid serious injury to the vertebral artery. Surgical results were satisfactory in 86% but the surgical timing was important since the results of cases with severe myelopathy was not always favorable. In conclusion, one-stage surgery is a very useful and effective method in cases with irreducible AAD and solid posterior fixation can be obtained by well-planned instrumentation.

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Instrumentation for craniovertebral junction may be characterized by the variety and complexity. Three techniques for craniovertebral fusion, such as the occipitocervical loop fixation, C1/C2 transarticular screw fixation, and anterior odontoid screw fixation are discussed, including indications, advantages and disadvantages, based on our experience of 12 cases. The occipitocervical loop fixation is a method to fix the occipital bone and the cervical laminae, using a metal loop and wires. Immediate and strong fixation of the craniovertebral junction is obtained, although restriction of postoperative neck movement is severe. We used this techniques in 7 cases without any complications. Postoperative stability was excellent except for 2 patients with rheumatoid arthritis, whose anterior C1 archs sank slightly in the early postoperative period. The C1/C2 transarticular screw fixation (Magerl) is a method to fix the C1 and the C2 using two screws inserted into the bilateral facet joints. This method allows one of the strongest fixation of the C1/C2 segments, while it has potential risk to the spinal roots and vertebral arteries. We used this technique in 4 cases of atlantoaxial dislocation with higher instability. Three of them were associated with os odontoideum and the other with SLE. Good fusion was obtained in all these cases. One patient showed asymptomatic neck bruit due to an arteriovenous fistula from the injured right vertebral artery. The patient was successfully treated by endovascular coil embolization without any complications. The anterior odontoid screw fixation is another method to fix a fractured odontoid processes using a single screw or double ones inserted via an anterior cervical approach. The advantage of this method is that it can preserve neck movement postoperatively. However, the indication is very limited to cases with acute odontoid fracture type II without disruption of the cruciform ligament. We used this method only in one case. In conclusion, the best method should be selected in each case among a variety of techniques of instrumentation for craniovertebral instability.

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The authors analysed the results of posterior fusions for craniocervical bone lesions. They were composed by 20 cases of one-stage transoral decompression and posterior fusion and 27 cases of simple posterior fusion. Among these, occipitocervical fusions were carried out in 26 cases with good bone fusions. For the case of long fusion, for example from occiput to C5, autologous long costal rib fragments were used and tightened by sublaminar wiring. Simple posterior cervical fusions (C1-C2 or C1-C2-C3) were made in 21 cases. Reduction loss was encountered in a case of Down syndrome. Fracture of sublaminar Songer cable wire was seen in one case and there were two cases of bone fusion failures which resulted in fibrous unions. To avoid these failures, more than three cable wires must be used for sublaminar wiring and /or more rigid external fixation using a halo-brace must be made.

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Introduction : Various surgical fixation techniques exist to obtain atlantoaxial stability. This study reports a retrospective review of 76 surgically treated cases through a standard posterior midline approach. Materials and Methods : There were 30 men and 46 women, the age range at the time of operation was 14 to 80 years. Forty-six had Rheumatoid arthritis (RA), 12 trauma, 8 Os odontoideum, 2 odontoid fracture, 1 von Recklinghausen's disease and 7 unknown. Forty-eight were treated with posterior wiring (modified McGraw; 41, Brooks; 7), 28 were treated with transarticular screw fixation (Magerl's method). All patients were followed with serial radiographs (lateral flexion-extension) until solid fusion or failure was documented. Results : There was no neurological deficit and no iatrogenic vascular injury. Thirty-nine of 48 (81.3%) with posterior wiring had osseous union, three had fibrous union but were stable, and six had non-union. Wire breakage was observed in two cases seemingly due to technical failure. Reoperations were performed in two patients, who were mutilans type and could not be applied a Halo vest because of severe RA. Magerl's method had gained osseous union without using a Halo vest in all patients. There was no difference in the fusion rate between cases with flexible cables or nylon threads. Loosening occurred in the flexible cable and the shape of the cable became to oval or ring-like. Postoperatively in 8 of 36 patients (22.2%) who had atlantoaxial arthrodesis, subaxial subluxation developed. Conclusion : The results obtained using Magerl's method were satisfactory. This method was useful for atlantoaxial subluxation and thought it rigid stability and solid fusion were obtained. Transarticular screw fixation and posterior bone graft supplemented by nylon thread to hold the graft achieves arthrodesis reliably.

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In spite of its well-documented usefulness for the resection of invaginated odontoid process, the transoral approach has an inherent drawback in that the operative field is deep, narrow, and contaminated. To circumvent these problems, the present authors employed the lateral approach for resection of the invaginated odontoid in two cases of basilar impression and in one case of cranial settling due to rheumatoid arthritis. With the patient in a lateral position, a U-shaped skin incision encompassing the posterior margin of the sternocleidomastoid (SCM), the inion, and the posterior midline was made. The SCM and the posterior cervical muscles were reflected anteriorly and inferiorly, respectively. After securing the vertebral artery, the lateral and posterior margin of the foramen magnum was widely resected to decompress the brain stem. Craniectomy was then enlarged anteriorly, drilling off the supero-posterior portion of the occipital condyle. Continuous resection of the jugular tuberculum anterior and superior to the hypoglossal canal with unroofing of the sigmoid sinus provided an ample working space, through which the invaginated odontoid could be well visualized and easily removed. Fixation between the occipit-C1 was carried out in none of the cases because the atlanto-axial sublaxation was irreducible preoperatively. In the case with cranial settling, since the patient had marked cord compression due to subluxation at C4-C5, posterior decompression of C4-C5 followed by the fixation from C1-C7 using an implantable titanium device was carried out. In every patient, the postoperative course was uneventful and the neurological deficit was markedly improved. The above experience indicates the feasibility of the lateral approach for the resection of invaginated odontoid. Furthermore, the lateral appoach is thought to have advantages over the transoral approach in that the operative field is clean and wide, the posterior fixation procedures can be simultaneously performed, and the patient's postoperative discomfort is much reduced. The operative technique for this lateral approach is described in detail and its merits and demerits as compared to the transoral approach are discussed.

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Effective surgical treatment of adhesive spinal arachnoiditis has not been established because of its complex clinical manifestations. In the present study, we retrospectively analyzed the clinical courses of 17 patients with adhesive spinal arachnoiditis who underwent surgical treatment in our institute between 1982 and 1996. The purpose of this study was to determine how to manage this disorder. CT-myelography and MRI revealed syringomyelia in 15 patients and cystic dilatation of the anterior subarachnoid space in 3 patients. All 17 cases presented paraparesis on admission. Two cases with hydrocephalus were treated with V-P shunt. Twelve cases underwent syringo-peritoneal shunt (S-P shunt, 10 cases) or syringo-subarachnoid shunt (S-S shunt, 2 cases). Three cases with cystic dilatation of the anterior subarachnoid space underwent laminectomy and opening of the cyst. Follow-up periods ranged from 1 month to 12 years (mean 4.6 years). Seven cases underwent additional operations for syringomyelia (S-P shunt 5, S-S shunt 2, lumbo-peritoneal shunt 2). In 3 cases, S-S shunt performed rostral to the site of adhesion was effective in long-term collapse of the syrinx. Alleviation of the symptoms was obtained in 10 cases (59%), while 3 cases (18%) showed progressive deterioration. Microcirculatory disturbance of the pial and subarachoid vessels and cystic changes around or in the spinal cord due to blockage of the cerebrospinal fluid are considered to be responsible for the pathogenesis of myelopathy. Drainage or shunting of the cerebrospinal fluid is essential in the treatment of this condition. S-S shunt can be an effective treatment in selected cases.

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We have recently reported that overcrowding of the posterior cranial fossa due to underdevelopment of the occipital bone induces hindbrain herniation in patients with adult type Chiari malformation. In the present report, we further performed morphometric study in Chiari patients associated with and without syringomyelia, to investigate the effect of the overcrowding on the development of the syringomyelia. Posterior fossa morphometry was performed in three groups : 26 adult patients with syringomyelia (syrinx group), 4 adult patients without syringomyelia (non-syrinx group) and 50 normal subjects (control group). The onset age and the association rate of basilar invagination in the syrinx group were not significantly different from those in the non-syrinx group. The syrinx group and non-syrinx group showed significantly shorter lengths in the supraoccipital and exoccipital portions of the occipital bone than the control group, although these lengths were not significantly different between the syrinx group and non-syrinx group. Among three groups, there were no significant differences in the axial lengths of the hindbrain, in the brain volume of the posterior fossa or in the cranial volume of the posterior cranial fossa. The volume ratio (the volume of the brain structure contained in the posterior cranial fossa divided by the volume of the posterior cranial fossa), which was regarded as one of the indicator of the crowdingness, was significantly larger in the syrinx group and non-syrinx group than that in the control group, though there was no significant difference between the syrinx group and non-syrinx group. The cerebellar tentorium in both syrinx group and non-syrinx group was significantly steeper than that in the control group. The results indicated that adult type Chiari malformation with or without syringomyelia had overcrowding in the posterior cranial fossa due to underdevelopment of the occipital bone. However, the degree of the overcrowding in the posterior cranial fossa have no direct effect on the development of the syringomyelia.

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In the present report, we studied the effect of cerebrospinal fluid drainage on experimental syringomyelia. (Materials and Methods) Experimental syringomyelia was induced by intracisternal injection of kaolin-saline solution to six Japanese white rabbits. Five weeks after the injection of kaolin-saline solution, the presence of hydrocephalus and syringomyelia was confirmed by magnetic resonance imaging (MRI). After confirmation of syringomyelic cavity, ventriculo-subgaleal shunt (V-S shunt) was performed to four rabbits. Cerebrospinal fluid (CSF) which collected in the subgaleal space was removed daily. One week after the V-S shunt, MRI showed the reduction of syringomyelic cavity in this rabbit. The brain and spinal cord specimens were investigated histologically. (Results) Syringomyelic cavity was reduced in size in the rabbit. The sections of upper and middle cervical spinal cord demonstrated the large parenchymal destruction and absence of ependymal lining. On the lower cervical and the upper thoracic spinal cord, the sections demonstrated the tear and deformation of the central canal. (Conclusion) We established the experimental model of syringomyelia which can be treated by cerebrospinal fluid shunting and evaluated by MRI.

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Vertebral arteries appear to be susceptible to injury at the time of cervical spine trauma because of their close anatomical relationship to the spine. However, ischemic symptoms rarely occur after cervical spine injury. The authors report three cases of vertebral artery dissection associated with cervical spine trauma. Case 1 is a 10-year-old boy who was hospitalized with cerebellar infarction following neck trauma. He had atlanto-axial dislocation and cerebral angiography revealed dissection of the left vertebral artery at the third segment. The patient underwent atlanto-axial arthrodesis and was discharged without any neurological deficits. Case 2 is a 53-year-old man with atlanto-axial rotatory fixation. He was suffering from neck pain and torticollis after injury. Although his right vertebral artery was occluded at the C5/6 segment, he didn't show any ischemic brain symptoms. Case 3 is a 49-year-old man with a past history of cervical spine trauma. He developed recurrent vertebrobasilar TIA. He had an unstable cervical spine at C4/5 and his left vertebral artery was occluded at C4/5 segment. His TIA disappeared after immobilization with neck collar. After anterior cervical discectomy with iliac bone fusion for C4/5, the patient was discharged without any unfavorable symptoms. Since vertebral artery dissection is not rare in cervical spine fracture or dislocation, vertebral angiography should be indicated for those who have ischemic brain symptoms after cervical traumas. Individualized management is needed to vertebral artery dissection with cervical spine fracture or dislocation.

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Motor evoked potential (MEP) monitoring was carried out in 32 consecutive patients (age 1 to 50 years) undergoing resection of intramedullary spinal cord tumors (IMSCTs). The response were elicited by high-voltage transcranial electrical stimulation and recorded with a catheter-electrode placed epi/subdurally at the caudal end of the laminectomy. Intraoperative MEPs were reliably recorded in 19 (59%) patients before myelotomy (monitorable group). MEPs were absent before myelotomy in 10 patients. In addition, difficulty in placing the recording electrode and large electrical noise precluded 3 patients from the monitoring. These 13 patients comprised the unmonitorable group. Postoperative significant worsening of the motor function was found in 1 patient in the monitorable group, compared to 5 patients in unmonitorable group. In the adult group (n=24), patients with monitorable MEPs (n=14) showed a statistically significant association with good surgical outcome (P<0.05). Good preoperative motor function showed only a weak association with good surgical outcome (P=0.13). Factors influencing the monitorability of MEPs were analyzed. Preoperative motor function (P<0.01), history of no previous treatment (P<0.01), and small tumor size (P<0.05) showed statistically significant association with monitorability of MEPs. These associations were absent in the pediatric group (n=8). Location of the tumor (Cervical vs. thoracic) did not affect the reliability of MEPs. We concluded that monitorable MEPs are a critical predictor of postoperative motor function for surgery of IMSCT in adult patients. MEPs of pediatric patients requires additional study, and it is premature to publish a definitive conclusion.

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