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Atsushi Sato

OBJECTIVE

Effective monitoring and application of visual evoked potentials (VEPs) during neurosurgery is a major challenge. While many monitoring methods have been effectively used, the use of VEPs as an objective determination method has not been established. The purpose of this report was to present a method for overcoming this limitation according to the use of a specific stimulus.

METHODS

Data analysis was performed in 26 cases of brain surgery. Observation was carried out for 2 groups of responses: the response derived from the start of light emission, described as the on response, and the response derived from the end of light emission, described as the off response. These reactions were separated by extending the light emission time. The waves from the visual cortex were selected from each reaction following the start and the end of light emission with consideration for the characteristics of the potential distribution. The waves were observed to characterize changes resulting from variations in duration and quantity of light emission. The results of the analysis were used to determine the optimal emission time and amount of light for effective use of wave components during VEP monitoring.

RESULTS

Stable and recordable waves were observed by monitoring the off response, consisting of the P1-N1-P2 component, with a wave latency of approximately 100 msec. Since the off response was correlated with the input, the stable wave derived from the off response could be adjusted by changing the light emission time and intensity. Individual differences in the latency of the off response were decreased by extending the light emission time and reducing the quantity of light. However, it was difficult to achieve stability by adjusting the light intensity and emission time using the on response. The off response was confirmed to be sufficiently stable for intraoperative monitoring. Moreover, during 1 case in which manipulation of the optic nerve was necessary, reduction in the off response was found to occur when the nerve was manipulated and to reverse when the manipulation stopped.

CONCLUSIONS

The off response was shown to have the capacity to function as a monitoring tool, providing more stable wave forms than the on response. Recording conditions could be adjusted to achieve a light-emitting time of 500 msec and a light quantity of 8000 Lx. Stable monitoring of VEPs using light-emitting stimuli can contribute toward improving surgical outcomes.

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Yukinari Kakizawa, Kazuhiro Hongo, Hisayoshi Takasawa, Yosuke Miyairi, Atsushi Sato, Yuichiro Tanaka and Shigeaki Kobayashi

✓ Three-dimensional (3D) neuroimages are generally considered useful for neurosurgical practice. Nevertheless, neuroimaging modalities such as 3D digital subtraction angiography and 3D computerized tomography angiography are still insufficient because the resulting images fail to delineate neural structures. Complex neurosurgical procedures are mostly performed in the cerebrospinal fluid (CSF) space of the basal cistern, where vessels and neural structures are present along with the lesion. The magnetic resonance (MR) imaging—derived 3D constructive interference in steady-state (CISS) imaging displays the margin between the CSF and neural structures, vessels, and dura mater in detail, in a two-dimensional fashion. The authors know that volume-rendered 3D CISS images would be more useful for surgery than conventional ones. Although the usefulness of “virtual MR image endoscopy” was reported previously, the endoscopic view is different from the operative field because of the perspective being emphasized. Therefore, to simulate surgical views, the authors made 3D neuroimages from a 3D CISS MR sequence by using an advanced computer workstation. After generating volume images, a cutting method was used in the desired plane to visualize the lesion with reference to a multiplanar reformatted image. The authors call these “real” 3D CISS images, and they are more comparable to the operative field. This newly developed method of producing a real 3D CISS image was used in 30 cases and contributed to the understanding of the relationship between a lesion and surrounding structures before attempting neurosurgical procedures, with minimal invasiveness to the patient.

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Yuichiro Tanaka, Shigeaki Kobayashi, Kazuhiro Hongo, Tsuyoshi Tada, Atsushi Sato and Hiroshi Takasuna

Object. The clinical and neuroimaging characteristics of hydrocephalus associated with vestibular schwannoma were retrospectively analyzed to improve the perioperative management of the circulation of cerebrospinal fluid.

Methods. A retrospective analysis was performed in 236 patients with unilateral vestibular schwannomas. The patients' ages ranged from 17 to 83 years (mean 53.6 ± 13.2 years), and the diameters of the tumors the patients harbored ranged from 5 to 60 mm (mean 30.5 ± 12.7 mm). Hydrocephalus was present before tumor resection in 33 patients (14%) and in six of these patients focal dilation of the sylvian fissures was noted. There was a significant correlation between the incidence of hydrocephalus and tumor size. The incidence of preoperative hydrocephalus among elderly patients (≥ 65 years of age) was 28.6% and that among younger patients (< 65 years of age) was 10.8%. Tumors in elderly patients with hydrocephalus (mean tumor diameter 32.8 ±11.7 mm; 12 patients) were significantly smaller than those in younger patients (mean tumor diameter 41.7 ± 10.9 mm; 21 patients). Among patients with tumors smaller than 30 mm (114 patients), the incidence of hydrocephalus in elderly patients (25%) was 12-fold higher than that in younger patients (2.1%). Six patients with hydrocephalus who had focal dilation of the sylvian fissures were significantly older than 27 patients with hydrocephalus in whom there was no focal dilation. The dilated sylvian fissures collapsed in two patients spontaneously after tumor resection and in the other four patients after shunt placement.

Conclusions. The incidence of associated hydrocephalus is higher in older patients. Communicating hydrocephalus tends to occur in elderly patients. Enlargement of the ventricles with focal dilation of the sylvian fissures should not be misinterpreted as physiological brain atrophy.

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Tetsuya Goto, Yuichiro Tanaka, Kunihiko Kodama, Shoji Yomo, Yosuke Hara, Atsushi Sato and Kazuhiro Hongo

✓ Intraoperative electrophysiological monitoring is essential for minimally invasive neurosurgery. The authors developed an innovative recording method using a staple electrode, consisting of a surgical skin staple and an integrated circuit (IC) test clip with a cable. The staple is put on the patient's skin after the induction of general anesthesia. After head fixation, the IC test clip is simply hooked to the staple. The authors used this method for recording in 158 consecutive cases. It took only a few minutes to set up 4–18 staple electrodes in each case. None of the staple electrodes became disconnected unintentionally, and the initial impedance was kept throughout the procedures. The authors conclude that the staple electrode is superior to conventional disc or needle electrodes in speed of setup, electrical stability, and cost-effectiveness and recommend its routine use for intraoperative electrophysiological monitoring.

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Sunao Takemura, Takamasa Kayama, Atsushi Kuge, Hasmat Ali, Yasuaki Kokubo, Shinya Sato, Hideyuki Kamii, Kaoru Goto and Takashi Yoshimoto

Object

Neural stem cells (NSCs) have been demonstrated in the subventricular zone (SVZ) of the lateral ventricle and the subgranular zone of the hippocampal dentate gyrus (DG). Although aging rats manifest a decrease in NSCs, rats exposed to stress (for example, ischemia, epilepsy, radiation, and trauma) show an increase in these cells. In transgenic mice, the overexpression of human copper/zinc superoxide dismutase (SOD1), an endogenous antioxidant, has been reported to be a protective enzyme against transient focal cerebral ischemia. The authors investigated the correlation between SOD1 and the proliferation of NSCs in aging as chronic oxidative stress (Experiment 1) and acute oxidative stress induced by transient focal cerebral ischemia (Experiment 2) in mice.

Methods

Bromodeoxyuridine (BrdU) was used in the evaluation of NSCs. In Experiment 1, NSCs in the SVZ significantly increased in 16-month-old transgenic mice compared with wild-type mice (p = 0.0001). In Experiment 2, mice were subjected to 30-minute occlusions of the middle cerebral artery. The increase in NSCs in the DG in transgenic mice was significantly greater than that in wild-type mice (p < 0.05).

Conclusions

Results in this study suggest that chronic and acute oxidative stress may inhibit the proliferation of NSCs and that SOD1 may play a key role in NSC proliferation.

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Jun Yoshida, Toshihiko Wakabayashi, Masaaki Mizuno, Kenichiro Sugita, Tazuka Yoshida, Shigeaki Hori, Teruaki Mori, Tomohiko Sato, Atsushi Karashima, Kaoru Kurisu, Katsuzo Kiya and Tohru Uozumi

✓ Recombinant human tumor necrosis factor-α was administered intra-arterially to treat 20 cases of malignant gliomas, mostly progressive or recurrent. The optimum dosage was determined to be 1 × 105 U/sq m/day. Among the 10 evaluable patients treated at this dosage, two responded (one completely and one partially), resulting in a 20% response rate. Side effects were mild and easily controllable. Improvement of neurological symptoms was noted in 47% of the patients a few days after treatment, even when computerized tomography showed no tumor regression. This might have been due to the pleiotypic biological activity of tumor necrosis factor-α. Neuroradiographic observations revealed narrowing of the tumor-feeding artery, a decrease in tumor staining ability, and necrosis in the central part of a tumor. The authors suggest that intra-arterial administration of tumor necrosis factor-α may be an effective treatment for malignant glioma, including recurrent cases.