Effective Extraocular Muscle Monitoring for Cranial Nerves III and VI Using 25 mm Insulated Needle Electrodes: A Case Report

In skull base surgery, preservation of the cranial nerve function of III and VI is an important consideration for maintaining the visual function and quality of life of patients. Nevertheless, intraoperative neurophysiological monitoring is not generally performed, mainly because of the technical difficulties in accurately inserting recording electrodes into the inferior rectus and lateral rectus muscles, which involve cranial nerves III and VI, respectively. In this case, electromyography (EMG) was monitored by inserting 25-mm insulated needle electrodes into the inferior rectus and lateral rectus muscles. As a result, clear EMG waveforms could be stably observed in both muscles. The patient recovered without extraocular muscle paralysis after surgery. This case shows that intraoperative extraocular muscle monitoring can help evaluate the function of the third and sixth cranial nerves, and suggests that monitoring with a 25-mm insulated needle electrode is an effective method.