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Katsushige Watanabe, Takashi Watanabe, Akio Takahashi, Nobuhito Saito, Masafumi Hirato and Tomio Sasaki

✓ The feasibility of high-frequency transcranial electrical stimulation (TES) through screw electrodes placed in the skull was investigated for use in intraoperative monitoring of the motor pathways in patients who are in a state of general anesthesia during cerebral and spinal operations.

Motor evoked potentials (MEPs) were elicited by TES with a train of five square-wave pulses (duration 400 µsec, intensity ≤ 200 mA, frequency 500 Hz) delivered through metal screw electrodes placed in the outer table of the skull over the primary motor cortex in 42 patients. Myogenic MEPs to anodal stimulation were recorded from the abductor pollicis brevis (APB) and tibialis anterior (TA) muscles. The mean threshold stimulation intensity was 48 ± 17 mA for the APB muscles, and 112 ± 35 mA for the TA muscles. The electrodes were firmly fixed at the site and were not dislodged by surgical manipulation throughout the operation. No adverse reactions attributable to the TES were observed.

Passing current through the screw electrodes stimulates the motor cortex more effectively than conventional methods of TES. The method is safe and inexpensive, and it is convenient for intraoperative monitoring of motor pathways.

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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.