Yoshihiro Natori

Microsurgical and magnetic resonance imaging anatomy of the cerebello-medullary fissure and its application during fourth ventricle surgery.

The cerebellomedullary fissure, the only entrance or exit to the fourth ventricle, is surrounded rostrally by the cerebellar tonsils and the biventral lobules and caudally by the medulla oblongata, the tela choroidea, and the lateral recesses. This fissure is an important route in operations on the fourth ventricle. We studied the microsurgical and magnetic resonance imaging (MRI) anatomy of the fissure by using autopsied normal cerebellum. MRI revealed that the fissure is visible as a slit and is indicated by the enhanced choroid plexus and the flocculus. Oriented by the anatomical information thus obtained, we have surgically treated nine patients with a tumor either in or around the fourth ventricle. Preoperative MRI clearly demonstrated the tumors in relation to the cerebellomedullary fissure. It revealed the precise anatomical location and extension of the tumor, not only its inferior extension but also its lateral one. The MRI findings and microsurgical anatomy of the cerebellomedullary fissure were quite useful for the removal of the tumors in the fourth ventricle.

Management of syringomyelia associated with chiari malformation: Comparative study of syrinx size and symptoms by magnetic resonance imaging

The authors reviewed the postoperative alteration of symptoms and syrinx size by magnetic resonance imaging (MRI) in 14 consecutive patients with syringomyelia associated with Chiari malformation. The patients were treated according to our treatment regimen and were divided into five groups according to operative modalities: (1) only foramen magnum decompression (D) for small syrinx; (2) D with ventriculoperitoneal (VP) shunt for small syrinx with hydrocephalus; (3) D with syringosubarachnoid (SS) shunt or (4) D with syringoperitoneal (SP) shunt for large syrinx; and (5) only VP shunt for syrinx with hydrocephalus and atlantoaxial dislocation, respectively. From the preoperative and postoperative sagittal MR images, the areas of the spinal cord and syrinx were measured by a digitizer and the syringo-cord (S-C) ratio was calculated. Out of 14 patients, 12 showed a reduction of syrinx size and a stabilization or improvement of symptoms after surgery. In the other two patients, the syrinx size did not change and their symptoms worsened. Magnetic resonance imaging follow-up showed that foramen magnum decompression without shunt is effective for patients with a small syrinx below 35% of the S-C ratio, and foramen magnum decompression with shunt was effective for patients with a large syrinx over 35% of the S-C ratio, but there was no significant difference between the SS and SP shunt group.

Results of a long-term follow-up after neuroendoscopic biopsy procedure and third ventriculostomy in patients with intracranial germinomas

OBJECT The authors report the results of long-term follow-ups in 12 patients with intracranial germinomas who underwent neuroendoscopic procedures before chemotherapy and radiotherapy, and discuss the usefulness and safety of these procedures. METHODS Between January 1996 and December 2005 at Kyushu University Hospital, 12 patients with intracranial germinomas underwent neuroendoscopic biopsy procedures involving a flexible fiberscope. Eight patients simultaneously underwent endoscopic third ventriculostomy (ETV) for existing obstructive hydrocephalus. All patients received chemotherapy and radiotherapy postoperatively, according to the regimen promulgated by the Japanese Pediatric Brain Tumor Study Group. The patients were followed for an average of 78.6 months (range 15-134 months), and a retrospective study was conducted. RESULTS Germinomas were histologically verified in all patients. No postoperative deaths or permanent morbidity was related to the neuroendoscopic procedures. No other cerebrospinal fluid diversion, such as that achieved with a ventriculoperitoneal shunt, was needed for the management of hydrocephalus. A complete response to postoperative chemotherapy and radiotherapy was achieved in all cases. Only one patient had a recurrent lesion in the spinal cord 6 years after the initial treatment; however, this patient had undergone only the neuroendoscopic biopsy procedure without ETV. CONCLUSIONS Neuroendoscopic procedures can permit a precise histological diagnosis of intracranial germinomas and are safe and effective in the management of hydrocephalus associated with these tumors. The risk of tumor dissemination due to the neuroendoscopic procedures appears to be minimal when the appropriate chemotherapy and radiotherapy are provided postoperatively.

Delayed effects of the microvascular decompression on hemifacial spasm: A retrospective study of 131 consecutive operated cases

Abstract We reviewed 131 consecutive cases operated for hemifacial spasm (HFS) by the same surgeon between January 1983 and April 1999. Microvascular decompression (MVD) was performed via lateral suboccipital approach. Post-operative follow-up ranged from 1.5 to 10 years (average 34 months). The final outcome divided into three categories, excellent (total recovery) in 120 cases (91.6%), partial ( > 75% recovery) in 4 cases (3.1%), and unchanged or recurrent in 7 cases (5.3%). Only 2 cases were re-operated, and final outcome of both was excellent. Based on these data, we aimed to determine a period of the final judgement of MVD effect and the causative factors of delayed effects on HFS retrospectively. There were102 complete recovered cases without hemifacial paralysis; immediate recovery from HFS was observed in 78 cases (76.5%), after 1 month in nine cases, 1-3 months in 5 cases, 3-6 months in 3 cases, 6-10 months in 2 cases, and 10-12 months in 5 cases. Thus, most cases were completely recovered within one year of observation. On the other hand, there was no statistically significant difference between immediate and delayed relief cases in clinical histories or operative observations. Therefore, our results suggest that the final judgement of the MVD effect could be made at least one year after surgery. [Neurol Res 2002; 24: 296-300]

Surgical anatomy of the anterior clinoid process

We studied the surgical anatomy of the anterior clinoid process (ACP) and its adjacent structures in cadaver heads. We paid special attention to the anatomical relationships between the ACP and adjacent structures to determine the surgical landmarks for safe anterior clinoidectomy. Thirty-five cadaver heads were dissected and the ACP regions were examined in 55 skull sides. We observed that in eight sides the ACP had been pneumatized from the sphenoid sinus. The caroticoclinoid foramen was revealed in only eight sides. The extra-ocular nerves ran forward to the superior orbital fissure at the inferolateral aspect of the ACP, with the oculomotor nerve being closest. The posterolateral area of the carotico-oculomotor membrane was thin and incomplete in nine sides. The study clarified the anatomical relationship between the ACP and its surrounding structures, and identified the major variations experienced. We used these to identify anatomical landmarks to assist the surgeon in the planning of a safe and effective anterior clinoidectomy.

An Indirect Revascularization Method in the Surgical Treatment of Moyamoya Disease

The indirect non-anastomotic bypass procedures for moyamoya disease are herein reviewed, and our multiple combined indirect procedure, i.e. a fronto-parieto-temporal combined indirect bypass procedure, is also introduced. Direct procedures such as superficial temporal artery-middle cerebral artery anastomosis are able to form collaterals with a high reliability, but these procedures are often difficult to technically perform in small children, and complications, when they occur, tend to be severe. Indirect procedures, such as encephalo-duro-arterio-synangiosis (EDAS), encephalo-myo-synangiosis (EMS), and encephalo-myo-arterio-synangiosis (EMAS) etc., are safe and easy and also successfully form collaterals especially in children with moyamoya disease. However, there are a few drawbacks with such procedures. They do not always form sufficient collaterals. The area where the original EDAS using the posterior branch of the superficial temporal artery can be done is also limited. Moreover, because the area covered by each single procedure is small, the collateral formation obtained by a single procedure is not always satisfactory. For these reasons we developed a fronto-temporoparietal combined indirect bypass procedure for child patients in order to overcome these problems. This multiple combined indirect procedure can cover a wider area of the ischemic brain through the EMAS in the frontal and the EDAS and EMS in the temporo-parietal regions. It is also safe and easy to perform, and one or two of these three procedures form sufficient collaterals with a relatively high reliability. This technique is described and the results are presented.

Surgical Treatment of Glossopharyngeal Neuralgia as Vascular Compression Syndrome via Transcondylar Fossa (Supracondylar Transjugular Tubercle) Approach

Summary Objective. These are the first reported cases in whom the transcondylar fossa approach was applied for the treatment of glossopharyngeal neuralgia (GPN) as a vascular compression syndrome. Cases Presentation. All three cases presented with severe paroxysmal pharyngeal pain which could not be controlled by medical treatment. The patients all underwent microvascular decompression surgery (MVD) via transcondylar fossa approach. The posterior inferior cerebellar artery or the anterior inferior cerebellar artery was clearly verified to be compressing the glossopharyngeal nerve and then was safely and completely moved and fixed to the dura mater by the sling retraction technique to effect decompression. No patient has since experienced any further pain or permanent neurological deficit after surgery. Technical Advantage. The transcondylar fossa approach is one of the lateral approaches which is different from the transcondylar approach. In this approach, the posterior part of the jugular tubercle is extradurally removed without injuring the atlanto-occipital joint. The entire course of the cisternal portion of the glossopharyngeal nerve can be sufficiently seen with gentle retraction of the cerebellar hemisphere, when using this approach. Conclusion. This approach makes the MVD for GPN both effective and safe.

Micro-anatomical study of the carotid cave

SummaryThe surgical treatment of aneurysms located in the carotid cave is often hazardous and difficult. We studied the micro-anatomy of the carotid cave and its neighbourhood by microscopic observation and histological examination using 50 sides from 25 autopsy cases. The carotid caves were found in 34 out of the 50 sides (68%) examined and were usually located in the posteromedial aspect of the carotid dural ring. They were classified into three types according to the topographic micro-anatomy: the slit-type (17/50, 34%) which showed a small, thin recess of the dura mater with fine connective tissue loosely adhered to the carotid wall; the pocket-type (12/50, 24%) which had a definite dural pouch with the apex attached to the vessel wall; and the mesh-type (5/50, 10%) which formed a slit- or pocket-type dural cave covered with a mesh-like dural roof. The remaining 16 sides (32%) showed tight dural attachment without any caval structure around the dural ring. The posteromedial portion of the carotid dural ring had no contact with any bony structure, and this distinct anatomical feature thus appear to facilitate the formation of the carotid cave. Furthermore, the availability of this potential space and the closely situated origin of the superior hypophyseal artery as well as the haemodynamic effect of the internal carotid artery may allow the development of the carotid cave aneurysm.

Surgical anatomy of the ophthalmic artery: its origin and proximal course.

OBJECTIVE: We examined the surgical anatomy of the ophthalmic artery (OA) by dissection of cadaver heads, evaluating the anatomic relationships between the origin of the OA and both its proximal course and surrounding structures. In addition, we demonstrated the surgical application of these anatomic features for safe surgical exploration of this region. METHODS: Through anatomic dissection, the origin of the OA was examined in both sides of 25 formalin-fixed and 10 fresh cadaver specimens. The following parameters were evaluated: the location of the origin of the OA in relation to the dural rings, the topographic relationship of the paraclinoid region, and the location of the dural penetrating point of the OA in the optic canal. RESULTS: The OA originated from the internal carotid artery within the intradural space in 49% of cases, just above the upper dural ring in 37%, at the clinoid segment in 7%, and within the cavernous sinus in 6%. The dural penetrating point of the OA was anterior to the falciform ligament, and thereby in the optic canal, in 74% of cases, ventral to the falciform ligament in 19%, and posterior to the falciform ligament in 7%. The anterior circumference point of the upper dural ring, the point at which the upper dural ring intersects the anterior edge of the internal carotid artery, was more anterior to the falciform ligament in 40% of cases and ventral and posterior to the falciform ligament in 16.4% and 43.6%, respectively. CONCLUSION: Our anatomic findings demonstrate anatomic variation of the OA in terms of its region of origin. Several anatomic points that were noteworthy during surgical exploration of this region are discussed.

Operative approaches to the pineal region tumors

Abstract Until the introduction of microsurgery, the surgical treatment of pineal region tumors had very poor results with high mortality and morbidity. However, there have been remarkable improvements with modern surgical technology and advanced knowledge. Now the main surgical approaches to pineal region tumors are the occipital transtentorial approach and the infratentorial supracerebellar approach. Recently the neuroendoscopic approach has been added. The surgical approach and any supplementary treatment should be selected in each case according to the nature of the individual tumor. The forms of treat-ment practiced by ourselves, including neuroendoscopic surgery, are presented, and the surgical treatments now applied are discussed.