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  • Author or Editor: Takamitsu Yamamoto x
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Chikashi Fukaya, Yoichi Katayama, Masahiko Kasai, Jun Kurihara and Takamitsu Yamamoto

✓ Intraoperative monitoring techniques for protecting the integrity of the oculomotor nerves during skull base surgery have been reported by several investigators, all of which involved the use of electromyographic responses to extraocular muscles. However, these techniques have not yet become popular because of the complexity of the procedures. The authors report an extremely simple and far more reliable technique in which electrooculographic (EOG) monitoring is used. The oculomotor nerves were stimulated with a monopolar electrode during skull base exposure. The polarity of the EOG responses recorded with surface electrodes placed on the skin around the eyeball yielded precise information concerning the location and function of the oculomotor and abducent nerves. In addition, with the aid of continuous EOG monitoring that detected transient changes in the background waves, surgical procedures that might impinge on oculomotor nerve function could be avoided. The present technique has been used in eight patients with skull base tumors and with it, the authors have achieved excellent results.

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Chikashi Fukaya, Yoichi Katayama, Masahiko Kasai, Jun Kurihara, Sadahiro Maejima and Takamitsu Yamamoto

Object. Histopathological studies on spinal cord injury (SCI) have demonstrated time-dependent spread of tissue damage during the initial several hours postinjury. When the long tract within the spinal cord is stimulated, a large monophasic positivity occurs at the injury site. This type of potential, termed the killed-end evoked potential (KEEP), indicates that a nerve impulse approaches but does not pass beyond the injury site. The authors tested the hypothesis that the damage spread can be evaluated as a progressive shift of the KEEP on a real-time basis. The effect of high-dose methylprednisolone sodium succinate (MPSS) on the spread of tissue damage was also examined by this methodology.

Methods. The KEEP was recorded using an electrode array placed on the spinal cord at the T-10 level in cats. This electrode array consisted of multiple 0.2-mm-diameter electrodes, each separated by 0.5 mm. Spinal cord injury was induced using a vascular clip (65 g pinching pressure for 30 seconds). The midline posterior surface of the spinal cord was stimulated bipolarly at the C-7 level by applying a single pulse at supramaximal intensity. During the initial period of 6 hours postinjury, the localization of the largest KEEP shifted progressively up to 2.5 mm rostral from the injury site. The amplitude of the KEEP recorded at the injury site decreased to 55 to 70% and became slightly shortened in latency as the localization of the largest KEEP shifted rostrally. These findings imply that the injury site KEEP represents the volume-conducted potential of the largest KEEP at the site of the conduction block. It moved away from the injury site in association with the damage spread, and this was confirmed histopathologically. A decrease in amplitude of KEEP at the injury site appeared to be the most sensitive measure of the damage spread, because the amplitude of the volume-conducted KEEP is inversely proportional to the square of the distance between the recording site and site of conduction block. Administered immediately after SCI, MPSS clearly inhibited these events, especially within 30 minutes postinjury.

Conclusions. The KEEP enables sequential evaluation to be made of the time-dependent spread of tissue damage in SCI in the same animal. It is, therefore, useful for detecting the effect of therapeutic interventions and for determining the therapeutic time window. The efficiency of MPSS to inhibit the spread of damaged tissue appeared to be maximized when it was administered within the initial 30-minute period postinjury.