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Han Soo Chang and Takaaki Kirino

✓ The indications for surgery on unruptured asymptomatic cerebral aneurysms are still unclear. In this report, the authors use mathematical methods to attempt to quantify the benefit of surgery for unruptured aneurysms.

Theoretical survival curves for either operative or conservative treatment were obtained by solving differential equations on the survival rate of a patient harboring an unruptured aneurysm. Patients' life expectancies were calculated as areas under these curves, and operative benefit was quantified as a gain in average life expectancy. To analyze morbidity, two concepts were introduced: premorbid survival rate and average premorbid survival period, and the operative gain of average premorbid survival period was calculated under certain assumptions.

Larger operative benefit was observed in younger patients, with increasingly less benefit in the elderly. The operative gain of average life expectancy was 3.9 years for a 40-year-old patient, 2.4 years for 50, 1.3 years for 60, and 0.6 years for a 70-year-old. Quantified operative benefit is presented in a table for various patient ages, yearly rupture rates, and expected operative morbidity and mortality.

This mathematical method would be useful to both surgeons and patients in making their decisions on surgery.

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Shinji Hotta, Akio Morita, Atsushi Seichi and Takaaki Kirino

✓ The authors report an unusual case of a patient with combined vertebral artery and Chiari malformation anomalies. Unless such anomalies are properly recognized prior to decompression and fusion, this condition can have grave surgical consequences. The diagnostic and surgery-related implications of such anomalous codiseases are discussed.

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Tomio Sasaki, Makoto Taniguchi, Ichiro Suzuki and Takaaki Kirino

✓ The authors report a new technique for en bloc petrosectomy using a Gigli saw as an alternative to drilling the petrous bone in the combined supra- and infratentorial approach or the transpetrosal—transtentorial approach. It is simple and easy and avoids postoperative cosmetic deformity. This technique has been performed in 11 petroclival lesions without injuring the semicircular canals, the cochlea, or the facial nerve.

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Yuhei Yoshimoto, Phyo Kim, Tomio Sasaki, Takaaki Kirino and Kintomo Takakura

✓ The present study was undertaken to determine whether oxyhemoglobin (OxyHb) is responsible for the functional alterations in the cerebral arteries observed during chronic vasospasm after subarachnoid hemorrhage. Vascular strips of canine basilar arteries were kept in organ culture for 3 days with or without repetitive exposure to OxyHb (OxyHb-treated and control strips). Contractions elicited by high levels of potassium (80 mM) and uridine 5′-triphosphate (3 × 10−4 M) were reduced in the OxyHb-treated group in a concentration-dependent manner. The relaxations evoked by nitric oxide and 8-bromo-cyclic guanosine monophosphate (8-bromo-cGMP) were not affected. Relaxations elicited by the calcium channel blocker, diltiazem, were attenuated in the OxyHb-treated rings. When the extracellular calcium concentration ([Ca++]e) was changed from a concentration in the external solution of 10−8 M to 10−3 M, myogenic tension developed. Myogenic tension, expressed as a percentage of the maximum contraction in each segment, was augmented in the OxyHb-treated group at [Ca++]e of 10−5 M and 10−4 M. There were no significant differences in passive compliance of the arterial wall between the two groups. These results demonstrated that prolonged exposure to OxyHb in vitro results in a decrease in contractile capacity and an increase in sensitivity to [Ca++]e, in agreement with previous findings in spastic arteries. By contrast, impairment of the 8-bromo-cGMP—mediated relaxation pathway and increased stiffness of the arterial wall, which have been reported to occur in spastic arteries, were not induced by prolonged exposure to OxyHb in vitro.

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Masanori Yoshino, Akio Morita, Junji Shibahara and Takaaki Kirino

P The authors report a case of a 16-year-old girl who presented with progressive gait difficulty 8 years after undergoing spinal radiation therapy for spinal astrocytoma. Magnetic resonance imaging revealed intramedullary multicentric cavity formation in the T4–10 area. Extensive subtotal resection was performed and a pathological examination of the excised tissue demonstrated cavernous malformation with radiation-induced degeneration in the surrounding vessels. This is believed to be the third case of de novo formation of an intramedullary cavernous malformation following spinal radiation therapy.

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Phyo Kim, Susumu Wakai, Seigo Matsuo, Takashi Moriyama and Takaaki Kirino

Hydroxyapatite (HA) is the main constituent of bone mineral, and synthetic HA serves as a biocompatible and bioactive material. It permits bone growth on its surface and forms a union with the adjacent bone.

Object. The authors have developed implants made of porous HA, which they have used in more than 90 cases in the past 6 years to achieve cervical interbody fusion. The implants were designed to provide maximum durability, biomechanical stability, and alignment preservation and to be technically easy to use. The authors summarize their experience and results with the use of these implants.

Methods. The results of postoperative follow-up observation of 12 months or longer (mean 37.1 ± 2.4 months) are available in 70 patients with underlying disease including: spondylosis, disc extrusion, ossification of the posterior longitudinal ligament (PLL), hypertrophy of the PLL, and trauma. The patients' ages at the time of surgery ranged from 22 to 83 years (mean 50.6 ± 1.3 years).

Flexion—extension radiographs and tomograms, obtained 6 and 12 months after surgery and every year thereafter, were used to demonstrate solid fusion in all cases. Dislocation of the implant occurred in three patients who were treated during the early portion of the series. At 6 to 12 months after surgery, encasement of the implant and formation of union were observed. Normal lordosis, if present prior to surgery, was maintained postsurgery. No neurological deterioration related to the site of fusion occurred during the period of observation.

Conclusions. The authors conclude that satisfactory interbody fusion can be achieved by using HA implants, provided their design is appropriate and adequate surgical techniques are used.

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Katsushige Watanabe, Nobuhito Saito, Makoto Taniguchi, Takaaki Kirino and Tomio Sasaki

Object. The frequency, nature, and history of subjective taste disturbance before and after vestibular schwannoma (VS) surgery was investigated.

Methods. Personal interviews were conducted in 108 patients with unilateral VS. Abnormalities in taste perception, either a significant reduction or a change in character, were experienced by 31 patients (28.7%) before surgery and by 37 (34.3%) after tumor removal. Preoperative taste disturbance worsened after surgery in five (16.1%) of the 31 patients, remained unchanged in eight (25.8%), improved in two (6.5%), and became normal in 16 (51.6%). Taste disturbance occurred postoperatively in 22 (28.6%) of 77 patients who had experienced no preoperative taste disturbance. The mean onset of the abnormality after resection was 1.1 ± 1.7 months. Postoperative taste disturbance resolved in 24 of the 37 patients (64.9%) within 1 year after onset.

Conclusions. Subjective taste disturbance was common before and after VS removal, and the natural history of this condition was very variable in the pre- and postoperative periods. All patients who undergo surgery for VS should receive appropriate counseling about the likelihood and course of postoperative complications, including dysfunction of the sensory component of the facial nerve.

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Kazuo Tsutsumi, Keisuke Ueki, Akio Morita and Takaaki Kirino

Object. Controversy still exists about the risk estimation for rupture of untreated saccular aneurysms presenting for causes other than subarachnoid hemorrhage (SAH). The object of this study was to address this issue.

Methods. Between January 1976 and December 1997 in the Aizu Chuou Hospital, 62 patients underwent observation for more than 6 months for saccular, nonthrombotic, noncalcified unruptured aneurysms at locations not related to the cavernous sinus, which were detected in cerebral angiography studies performed for causes other than SAH. Clinical follow-up data in those 62 patients were reviewed to identify the risk of SAH.

All patients were followed until July 1998, with the observation period ranging from 6 months to 17 years (mean 4.3 years). Seven patients (11.3%) developed SAH confirmed on computerized tomography (CT) scanning at a mean interval of 4.8 years, six of whom died and one of whom recovered with a major deficit. In addition, one patient died of the mass effect of the aneurysm, and another after sudden onset of headache and vomiting. The 5- and 10-year cumulative risks of CT-confirmed SAH calculated by the Kaplan—Meier method were 7.5% and 22.1%, respectively, for total cases, 33.5% and 55.9%, respectively, for large (> 10 mm) aneurysms, and 4.5% and 13.9%, respectively, for small (< 10 mm) aneurysms.

Conclusions. Although based on a relatively small, single-institution series, our data indicated that the risk of rupture from incidental, intradural, saccular aneurysms was higher than previously reported, and may support preventive surgical treatment of incidental aneurysms, considering the fatality rate of SAH.

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Masahiro Shin, Akio Morita, Shuichiro Asano, Keisuke Ueki and Takaaki Kirino

✓ Isolated fourth ventricle (IFV) is a rare complication in patients who undergo shunt placement, and it is not easily corrected by surgical procedures. The authors report a case of IFV that was successfully treated with an aqueductal stent placed under direct visualization by using a neuroendoscope. This 36-year-old suffered meningitis after partial resection of a brainstem pilocytic astrocytoma, and subsequently developed hydrocephalus for which a ventriculoperitoneal shunt was placed. Nine months later, the patient presented with progressive cerebellar ataxia, and magnetic resonance imaging revealed slitlike supratentorial ventricles and a markedly enlarged fourth ventricle, which were compatible with the diagnosis of IFV. The surgical procedure described was performed under visualization through a styletlike slim optic fiberscope inserted into a ventricular catheter. The catheter, with the endoscope inside it, was passed through the foramen of Monro and then through the aqueduct to reach the enlarged fourth ventricle, where membranous occlusion of the foramen of Magendie was clearly visualized. The tip of the catheter was placed in the fastigium of the fourth ventricle. After the procedure, the size of the fourth ventricle was reduced and the patient's symptoms improved. Thus, it is concluded that endoscopic aqueductal stent placement is a simple and safe surgical procedure for treatment of IFV.