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Kazutoshi Hida and Yoshinobu Iwasaki

Object

The authors describe the surgical procedures for placing syringosubarachnoid shunts and the results of surgery, as well as the prevention of shunt malfunction.

Methods

The series consisted of 59 patients with syringomyelia associated with Chiari I malformation in whom syringosubarachnoid shunts were placed. Their ages ranged from 4 to 62 years (median 28 years). The follow-up period ranged from 13 to 219 months. The authors principally implanted the shunts in patients with large-sized syringes. Neurological improvement was satisfactory, and postoperative magnetic resonance imaging demonstrated that the syringes had resolved or decreased in size in all patients. Reoperation was necessary in 10 patients who were treated before 1993.

Conclusions

To prevent shunt malfunction, both dorsal root entry zone myelotomy and placement of the syringo-subarachnoid shunt tube into the ventral subarachnoid space are useful.

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Jangbo Lee, Kazutoshi Hida, Toshitaka Seki and Yoshinobu Iwasaki

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Izumi Koyanagi, Yoshinobu Iwasaki, Kazutoshi Hida, Hiroyuki Imamura and Hiroshi Abe

Object. Because of the lack of magnetic resonance (MR) signal from cortical bones, MR imaging is inadequate for diagnosing ossified lesions in the spinal canal. However, MR imaging provides important information on spinal cord morphology and associated soft-tissue abnormality. The purpose of this study is to determine the role of MR imaging in the diagnosis and treatment of patients with ossification of the posterior longitudinal ligament (OPLL) of the cervical spine.

Methods. The authors reviewed MR imaging findings in 42 patients with cervical OPLL who were examined with a superconducting MR imaging system. The types of OPLL reviewed included eight cases of continuous, 21 cases of segmental, and 13 cases of the mixed type. All patients were treated surgically either by anterior (26 cases) or posterior decompression (16 cases).

Conclusions. The T1-weighted images clearly demonstrated the spinal cord deformity caused by OPLL. Associated disc protrusion was found to be present at the maximum compression level in 60% of the patients in this series. The highest incidence of disc protrusion (81%) was found in patients with segmental OPLL. Intramedullary hyperintensity on T2*-weighted imaging was noted in 18 patients (43%). The neurological deficits observed in these 18 patients were significantly more severe than those observed in the other 24 patients. Postoperative MR imaging revealed improvement in the spinal cord deformity, although the intramedullary hyperintensity was still observed in most cases. The present study demonstrates the importance of associated disc protrusion in the development of myelopathy in patients with cervical OPLL. Magnetic resonance imaging findings may be used to help determine the actual levels of spinal cord compression and to suggest the method of surgical treatment.

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Kazutoshi Hida, Yoshinobu Iwasaki, Katsuya Goto, Kazuo Miyasaka and Hiroshi Abe

Object. This retrospective study was performed to evaluate the results of surgical treatment and the use of preoperative embolization in managing patients with perimedullary arteriovenous fistulas (AVFs).

Methods. The authors studied 20 consecutive patients with perimedullary AVFs who underwent surgical treatment. Arteriovenous shunts were at the level of the cervical spine in five patients, the thoracic spine in 12, and the conus medullaris in three patients. Of the 20 AVFs, three were fed by the anterior spinal artery only, three by the posterior spinal artery, and 14 by both the anterior and posterior spinal arteries. Nine patients had varices that compressed the spinal cord. Eleven patients underwent surgery, and nine patients underwent surgery combined with adjuvant preoperative embolization.

Preoperative embolization remarkably reduced blood flow through the AVFs and facilitated subsequent surgical procedures. Postoperative angiography revealed complete disappearance of the AVFs in 16 patients. However, small fistulas persisted in the other four patients, whose large lesions were fed by the anterior spinal artery. Postoperatively, neurological status was improved in 11 patients, unchanged in eight, and worse in one patient.

Conclusions. Effective interruption of a spinal arteriovenous shunt was achieved by surgery in all cases, even when the anterior spinal artery was involved. For large and high-flow AVFs, embolization proved to be a useful adjunct to surgery.

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Kazutoshi Hida, Yoshinobu Iwasaki, Katsuya Goto, Kazuo Miyasaka and Hiroshi Abe

This retrospective study was performed to evaluate the results of surgical treatment and the use of preoperative embolization in managing perimedullary arteriovenous fistulas (AVFs).

The authors studied 20 consecutive patients with perimedullary AVFs who underwent surgical treatment. Arteriovenous shunts were at the level of the cervical spine in five patients, the thoracic spine in 12, and the conus medullaris in three patients. Of the 20 AVFs, three were fed by the anterior spinal artery only, three by the posterior spinal artery, and 14 by both the anterior and posterior spinal arteries. Nine patients had varices that compressed the spinal cord. Eleven patients underwent surgery alone, and 9 patients underwent surgery combined with adjuvant preoperative embolization.

Preoperative embolization remarkably reduced the blood flow through AVFs and facilitated subsequent surgical procedures. Postoperative angiography revealed complete disappearance of the AVF in 16 patients. However, small fistulas persisted in the other four patients whose large lesions were fed by the anterior spinal artery. Neurological status was improved in 11 patients, unchanged in eight, and worse in one patient postsurgery.

Effective interruption of a spinal AV shunt was obtained by surgery in all cases, even when the anterior spinal artery was involved. For large and high-flow AVFs, embolization proved to be a useful adjunct to surgery.

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Jangbo Lee, Izumi Koyanagi, Kazutoshi Hida, Toshitaka Seki, Yoshinobu Iwasaki and Kenji Mitsumori

Object

Spinal cord edema is a rare radiological finding in chronic degenerative disorders of the spine. Between 1997 and 2001, the authors treated six patients with cervical spondylotic myelopathy in whom postoperative spinal cord edema was demonstrated. The authors describe the radiological and clinical features of this unusual condition.

Methods

The six patients were all men, and ranged in age from 44 to 72 years. All patients presented with mild quadriparesis and underwent laminoplasty or anterior fusion. Preoperative magnetic resonance (MR) imaging revealed marked spinal cord compression with intramedullary hyperintensity on T2-weighted sequences and spinal cord enhancement at the compression level after administration of Gd.

After surgery, spinal cord edema was observed in all patients; the spinal cord appeared swollen on the postoperative MR images. Preoperative and postoperative Gd-enhanced MR imaging demonstrated clear enhancement of the white matter at the compressed segment. Neurologically, five of six patients experienced good improvement of symptoms; however, the spinal cord edema as documented on follow-up MR imaging persisted for several months after surgery.

Conclusions

The radiological characterization of spinal cord edema was based on the reversible white matter lesion most likely caused by disturbed local venous circulation induced by chronic spinal cord compression. Such unusual MR findings in cervical spondylotic myelopathy should be differentiated from intramedullary spinal cord tumors, demyelinating disorders, or inflammatory processes.

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Ki Hong Cho, Yoshinobu Iwasaki, Hiroyuki Imamura, Kazutoshi Hida and Hiroshi Abe

✓ An experimental model was devised to elucidate the role of spinal blockade in posttraumatic syringomyelia. Thirty-eight Japanese White rabbits, each weighing about 3 kg, were used in this study. The animals were divided into four groups: in Group 1, eight animals received traumatic injury only; in Group 2, 12 animals received traumatic injury following injection of 100 mg kaolin suspended in 1 cc normal saline solution into the subarachnoid space at the site of trauma; in Group 3, nine animals received traumatic injury following injection of 200 mg kaolin in 1 cc normal saline solution into the subarachnoid space at the site of trauma; and in Group 4, nine animals without traumatic injury received an injection of 200 mg kaolin in 1 cc normal saline solution into the subarachnoid space.

The subjective criteria for syrinx formation were the presence of a definite round cyst having a smooth margin and an upper or lower extension of more than 2 cm from the injured site. Syrinx formation was seen in 12.5% (one of eight rabbits) in Group 1, 41.7% (five of 12 animals) in Group 2, 55.5% (five of nine rabbits) in Group 3 and 0% (none of nine animals) in Group 4 (p < 0.05). There was a tendency for the combined trauma/kaolin injection groups to be more prone to develop a syrinx. In the kaolin injection only group (Group 4), no animal showed a definite cyst or an extending cavity during the experimental period. The results suggest that kaolin enhances the extension of multiple small cavities that have already formed at the time of initial injury. The difference between the frequency of syrinx formation and the time of survival was statistically significant well beyond the 0.05% level. The overall difference, relating to the frequency of syrinx development, group, and duration of survival, was also statistically significant. In summary, subarachnoid block secondary to adhesive arachnoiditis is important in initiating the extension of the syringomyelia cavity.

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Izumi Koyanagi, Yoshinobu Iwasaki, Kazutoshi Hida, Minoru Akino, Hiroyuki Imamura and Hiroshi Abe

Object. It is known that the spinal cord can sustain traumatic injury without associated injury of the spinal column in some conditions, such as a flexible spinal column or preexisting narrowed spinal canal. The purpose of this study was to characterize the clinical features and to understand the mechanisms in cases of acute cervical cord injury in which fracture or dislocation of the cervical spine has not occurred.

Methods. Eighty-nine patients who sustained an acute cervical cord injury were treated in our hospitals between 1990 and 1998. In 42 patients (47%) no bone injuries of the cervical spine were demonstrated, and this group was retrospectively analyzed. There were 35 men and seven women, aged 19 to 81 years (mean 58.9 years). The initial neurological examination indicated complete injury in five patients, whereas incomplete injury was demonstrated in 37.

In the majority of the patients (90%) the authors found degenerative changes of the cervical spine such as spondylosis (22 cases) or ossification of the posterior longitudinal ligament (16 cases). The mean sagittal diameter of the cervical spinal canal, as measured on computerized tomography scans, was significantly narrower than that obtained in the control patients. Magnetic resonance (MR) imaging revealed spinal cord compression in 93% and paravertebral soft-tissue injuries in 58% of the patients.

Conclusions. Degenerative changes of the cervical spine and developmental narrowing of the spinal canal are important preexisting factors. In the acute stage MR imaging is useful to understand the level and mechanisms of spinal cord injury. The fact that a significant number of the patients were found to have spinal cord compression despite the absence of bone injuries of the spinal column indicates that future investigations into surgical treatment of this type of injury are necessary.

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Kazutoshi Hida, Yoshinobu Iwasaki and Minoru Akino

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Kazutoshi Hida, Hiroki Shirato, Toyohiko Isu, Toshitaka Seki, Rikiya Onimaru, Hidefumi Aoyama, Satoshi Ushikoshi, Kazuo Miyasaka and Yoshinobu Iwasaki

Object

Radiosurgical treatment of spinal arteriovenous malformations (AVMs) is becoming a practical therapeutic option as methodology improves, but no comparative study has yet been published on focal fractionated radiotherapy. The authors report their experience with conventional and hypofractionated radiotherapy for spinal AVM.

Methods

Candidates for this study were patients who experienced symptoms due to an intramedullary AVM but were ineligible for embolization or surgery. Of 21 patients with spinal AVMs, 10 cases in a 10-year period met this criterion. Angiography and contrast-enhanced computerized tomography scanning were used for treatment planning in all cases. Fractionated radiotherapy was performed using a linear accelerator, extracranial immobilization system, and frequent orthogonal linacographic verification. The starting radiation dose was 32 Gy in two, 36 Gy in three, and 40 Gy in two patients, in a regimen involving 1.8 to 2—Gy daily fractions; this was recently changed to a hypofractionation schedule of 30 Gy (in eight sessions) in one and 20 Gy (in four sessions) in two patients.

Results

The follow-up period ranged from 26 to 124 months (median of 49 months). There were no hemorrhages nor any adverse reactions attributable to irradiation. Of the seven patients who consented to undergo follow-up angiography, the nidus size decreased in five, but complete obliteration did not occur in any patient.

Conclusions

Because no patient experienced adverse effects, the maximum tolerable radiation dose for the spinal cord associated with an AVM could not be identified, although it presumably is higher than those administered. The lack of rebleeding in patients in whom complete angiographic occlusion was absent suggests that the natural history of spinal AVMs may be less aggressive than previously reported.