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Takanori Fukushima

✓ A new 1.45-mm endoscope is described that can be inserted through a thin-walled No. 16 needle. The instrument was used in 10 cadavers for endoscopic exploration of the cisterna magna, the C1–2 space, Meckel's cave, and the cerebellopontine angle. Its potential clinical application is discussed.

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Takanori Fukushima and Keiji Sano

✓ A new modification of the transseptal, transsphenoidal approach to the sella turcica is described. The procedure consists of unilateral dissection of the septal mucosa through a sublabial route, and retraction of the entire nasal septum with its upper attachment as a hinge. For mobilization of the septum, an L-shaped osteotomy is made along the base of the septum and along the anterior wall of the sphenoid sinus. It provides adequate exposure of the sphenoid sinus while preserving the septal structures. The anterior nasal spine and the edges of the nares are also left intact. The anterior wall of the sphenoid sinus is resected en bloc and is used as a bone splint for the reconstruction of the sellar floor. This approach has been performed in 45 cases of pituitary adenoma, one of craniopharyngioma, and one with sphenoid mucocele. There was no instance of complications such as mucosal perforation, septal deformity, or infection. Modifications of the surgical instruments used are described.

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William T. Couldwell and Takanori Fukushima

✓ The authors describe a cosmetic mastoidectomy technique for use when performing a combined supra/infratentorial craniotomy and transtemporal exposure. The technique involves a single temporal suboccipital bone flap and cosmetic mastoidectomy, removing the outer table of bone for later replacement. Replacement of the outer table of mastoid bone enables tamponade of a fat graft against the dura to reduce the risk of postoperative cerebrospinal fluid leaks. The technique has been performed in eight patients treated for petroclival meningiomas with excellent cosmetic results.

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Observations on synkinesis in patients with hemifacial spasm

Effect of microvascular decompression and etiological considerations

Phyo Kim and Takanori Fukushima

✓ In 95 patients with hemifacial spasm, synkinetic actions were measured objectively using electromyographic examination of the blink reflex and impedance audiometry. Abnormal synkinesis between the orbicularis oculi and the orbicularis oris muscles was recorded in 93% of cases, while synkinesis between the stapedius muscle and the facial muscles was recorded in 87%. Neither of these effects could be demonstrated on the unaffected side. The examinations were performed before and after microvascular decompression in 66 cases. Rapid disappearance of synkinesis, often within 10 days, was observed after the relief of vascular compression in 81% of patients who had not undergone previous peripheral facial nerve block procedures. These findings indicate that the synkinesis seen in hemifacial spasm is essentially a reversible condition, and suggest that axonal ephaptic conduction at the vascular compression site plays an important role in the pathophysiological mechanism of hemifacial spasm.

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Shinichiro Miyazaki, Takanori Fukushima, and Takamitsu Fujimaki

✓ Two patients with large high-cervical paragangliomas were treated with radical resection and placement of a cervical-to-petrous internal carotid artery saphenous vein bypass. The high-cervical and infratemporal segments of the internal carotid artery engulfed within the tumor were resected and successfully replaced with a saphenous vein interposition graft. The postoperative course was uneventful in both cases and follow-up angiography revealed satisfactory reconstruction of the high-cervical and infratemporal skull base carotid artery. The operative technique, indications, and potential future applications of this newly developed skull base bypass procedure are discussed.

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Experimental spinal cord injury produced by slow, graded compression

Alterations of cortical and spinal evoked potentials

Johannes Schramm, Keizo Hashizume, Takanori Fukushima, and Hiroshi Takahashi

✓ A new model of experimental spinal cord injury produced by slow, graded compression in cats is described. The extent of cord compression was evaluated by monitoring somatosensory evoked potentials (SEP's). The compression was exerted by means of a special screw-plate assembly with stepwise advancement of the compression plate at different time intervals and was completed when cortical SEP had disappeared. Every stage in the total course of gradual compression was expressed as a percentage of the total. Cortical and spinal SEP's were recorded at each increment. The SEP pattern was analyzed in terms of latency, amplitude, and wave form. It was noteworthy that SEP's were remarkably resistant to gradual compression. The amplitude of cortical SEP's began decreasing at a late stage of compression, usually at about 80% of total compression, and that of spinal SEP's some time earlier, at about 60% of total compression. They both then rapidly fell to zero. Cortical SEP's showed a slight increase in latency concurrent with the reduction of amplitude, while the latency of spinal SEP's was constant. Mid-thoracic SEP's showed considerable individual variation in wave form. Their changes were similar to those of cortical SEP. Thoracolumbar SEP's, recorded immediately rostral to the compression, showed little individual variation, and did not show flat recordings even with maximum compression. A small monophasic positive wave was present in all animals even after the cortical SEP's became flat. This “final potential” was assumed to be caused by electrotonic volume conduction from the activities of the dorsal white matter caudal to the compression site. The reversibility of SEP's after the release of compression was remarkable. Both cortical and spinal SEP's could show complete recovery even when histological examination demonstrated hemorrhagic necrosis. The present data show no linear correlation between SEP changes and degree of compression. There are no changes with slight or moderate degree of compression. Alterations of SEP's in slow compression models should suggest the presence of a severe degree of compression.

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Takamitsu Fujimaki, Takanori Fukushima, and Shinichiro Miyazaki

✓ The results in 122 patients with trigeminal neuralgia who underwent percutaneous retrogasserian glycerol injection are presented. Eighty patients were followed from 38 to 54 months. The recurrence rate at 54 months was 72% (Kaplan-Meier analysis), and the median pain-free interval was 32 months. Complications associated with the procedure were significantly high: 63% of the patients had definite hypesthesia of the face and 29% had unpleasant dysesthesias, including two cases of anesthesia dolorosa. Sensory disturbances were most frequent in patients who had received a previous alcohol block procedure. Among the patients without previous peripheral procedures, 50% developed sensory disturbances. Because of the high rates of recurrence and sensory disturbances, the authors prefer microvascular decompression for the management of trigeminal neuralgia.

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J. Diaz Day, Steven L. Giannotta, and Takanori Fukushima

✓ Surgical access to the parasellar, infrachiasmatic, and posterior clinoid regions has traditionally been accomplished through an intradural pterional or subtemporal approach. However, for large or complex lesions in these locations, such traditional trajectories may not afford sufficient exposure for complete obliteration of the pathological process. The authors describe an anterolateral transcavernous approach to this region that includes the following components: 1) extradural removal of the sphenoid wing and exposure of the superior orbital fissure and foramen rotundum; 2) removal of the anterior clinoid process via the anterolateral route; 3) decompression of the optic canal; 4) extradural retraction of the temporal tip; 5) transcavernous mobilization of the carotid artery and third cranial nerve; and 6) removal of the posterior clinoid process. This method results in enhanced exposure with minimal brain retraction and preservation of the temporal tip bridging veins.

This approach has been used in 22 patients: 10 with basilar top aneurysms, eight with craniopharyngiomas, one with a tuberculum sellae meningioma, and two with trigeminal neuromas; the last patient had a carotidcavernous fistula and a concomitant pituitary adenoma. Complete clip ligation was performed for all 10 basilar artery aneurysms, and gross total resection was achieved with preservation of the pituitary stalk in all tumor cases. Microscopic total resection was not possible in two cases of craniopharyngioma due to hypothalamic invasion. Two patients suffered transient postoperative hemiparesis, and one patient has persisting weakness; however, no patient followed for more than 6 months suffered any persistent cranial nerve morbidity. It is concluded that this procedure can serve as an alternative to either the transsylvian or subtemporal approaches when cranial base pathologies are large or complex.

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Katsuyuki Asaoka, Yutaka Sawamura, Masabumi Nagashima, and Takanori Fukushima

Object. In this study the authors investigated the histomorphometric background and microsurgical anatomy associated with surgically created direct hypoglossal—facial nerve side-to-end communication or nerve “anastomosis.”

Methods. Histomorphometric analyses of the facial and hypoglossal nerves were performed using 24 cadaveric specimens and three surgically obtained specimens of severed facial nerve. Both the hypoglossal nerve at the level of the atlas and the facial nerve just distal to the external genu were monofascicular. The number of myelinated axons in the facial nerve (7228 ± 950) was 73.2% of those in the normal hypoglossal nerve (9778 ± 1516). Myelinated fibers in injured facial nerves were remarkably decreased in number. The cross-sectioned area of the normal facial nerve (0.948 mm2) accounted for 61.5% of the area of the hypoglossal nerve (1.541 mm2), whereas that of the injured facial nerve (0.66 mm2) was less than 50% of the area of the hypoglossal nerve. Surgical dissection and morphometric measurements were performed using 18 sides of 11 adult cadaver heads. The length of the facial nerve from the pes anserinus to the external genu ranged from 22 to 42 mm (mean 30.5 ± 4.4 mm). The distance from the pes anserinus to the nearest point on the hypoglossal nerve ranged from 14 to 22 mm (mean 17.3 ± 2.5 mm). The former was always longer than the latter; the excess ranged from 6 to 20 mm (mean 13.1 ± 3.4 mm). Surgical anatomy and procedures used to accomplish the nerve connection are described.

Conclusions. The size of a half-cut end of the hypoglossal nerve matches a cut end of the injured facial nerve very well. By using the technique described, a length of facial nerve sufficient to achieve a tensionless communication can consistently be obtained.