• Masahiro Nonaka, Takeshi Itakura, Haruka Kawano, Ryosuke Matsuno, Taichi Omachi, Haruna Isozaki, Takamasa Kamei, Junichi Takeda, and Akio Asai.
• Department of Neurosurgery, Kansai Medical University, Hirakata City, Osaka, Japan. Electronic address: nonakamasa65@gmail.com.
• World Neurosurg. 2021 Aug 1; 152: 56-60.

BackgroundWe describe a continuous monitoring method aimed at preserving nerve function during biopsy of lesions on the oculomotor nerve using stimulation of the oculomotor nerve proximal to the lesion.Case DescriptionA 5-year-old girl with a recurrent left oculomotor nerve palsy and contrast-enhancing left oculomotor nerve mass on magnetic resonance imaging underwent a biopsy of the lesion to aid in its diagnosis. At the time of surgery, needle electrodes were inserted into the superior and inferior rectus muscles percutaneously, and cotton-covered electrodes were implanted into the oculomotor nerve proximal to the lesion. Compound muscle action potentials of the oculomotor nerve were measured continuously by monopolar stimulation. The lesion was mapped by direct stimulation, and the unresponsive area was excised. The amplitude of the compound muscle action potentials decreased during the resection but recovered postoperatively. After resection of the lesion, the compound muscle action potentials remained the same as they were preoperatively. No obvious postoperative oculomotor nerve palsy was observed.ConclusionsThis method of continuous monitoring of the function of the oculomotor nerve is simple to use and is suitable for lesions in close proximity to the oculomotor nerve.Copyright © 2021 Elsevier Inc. All rights reserved.

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