J Korean Neurosurg Soc.  2021 Mar;64(2):282-288. 10.3340/jkns.2020.0179.

Triggered Electrooculography for Identification of Oculomotor and Abducens Nerves during Skull Base Surgery

• Jeong HN
• Ahn SI
• Na M
• Yoo J
• Kim W
• Jung IH
• Kang S
• Kim SM
• Shin HY
• Chang JH
• Kim EH

• KMID: 2513859
• DOI: http://doi.org/10.3340/jkns.2020.0179

Abstract

Objective
: Electrooculography (EOG) records eyeball movements as changes in the potential difference between the negatively charged retina and the positively charged cornea. We aimed to investigate whether reliable EOG waveforms can be evoked by electrical stimulation of the oculomotor and abducens nerves during skull base surgery.
Methods
: We retrospectively reviewed the records of 18 patients who had undergone a skull base tumor surgery using EOG (11 craniotomies and seven endonasal endoscopic surgeries). Stimulation was performed at 5 Hz with a stimulus duration of 200 μs and an intensity of 0.1–5 mA using a concentric bipolar probe. Recording electrodes were placed on the upper (active) and lower (reference) eyelids, and on the outer corners of both eyes; the active electrode was placed on the contralateral side.
Results
: Reproducibly triggered EOG waveforms were observed in all cases. Electrical stimulation of cranial nerves (CNs) III and VI elicited positive waveforms and negative waveforms, respectively, in the horizontal recording. The median latencies were 3.1 and 0.5 ms for craniotomies and endonasal endoscopic surgeries, respectively (p=0.007). Additionally, the median amplitudes were 33.7 and 46.4 μV for craniotomies and endonasal endoscopic surgeries, respectively (p=0.40).
Conclusion
: This study showed reliably triggered EOG waveforms with stimulation of CNs III and VI during skull base surgery. The latency was different according to the point of stimulation and thus predictable. As EOG is noninvasive and relatively easy to perform, it can be used to identify the ocular motor nerves during surgeries as an alternative of electromyography.

Keyword

Abducens nerve; Electrooculography; Monitoring, Intraoperative; Oculomotor nerve

Figure

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  Fig. 1. A schematic design showing the placement of electrodes for the intraoperative electrooculography. R : reference electrode, A : active electrode.

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  Fig. 2. T1-weighted coronal (A) and fluid attenuated inversion recovery axial (B) magnetic resonance images with enhancement showed left anterior clinoid process meningioma. The triggered electrooculographic responses of left eye in horizontal recording showed the biphasic positive waveforms with a latency of 0.5 ms and an amplitude of 50 μV when stimulating left oculomotor nerve at a stimulation intensity of 1 mA (C) and the biphasic negative waveforms with a latency of 0.5 ms and an amplitude of 75 μV when stimulating left abducens nerve at a stimulation intensity of 2 mA (D).

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  Fig. 3. T1-weighted coronal (A) and axial (B) magnetic resonance images with enhancement showed left petrous meningioma. The triggered electrooculographic responses of left eye in horizontal recording showed the monophasic negative waveforms with a latency of 3.2 ms and an amplitude of 27 μV (C) when stimulating left abducens nerve at a stimulation intensity of 0.2 mA (D).

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  Fig. 4. T1-weighted coronal (A) and axial (B) magnetic resonance images with enhancement showed recurrent craniopharyngioma in right sellar area. The triggered electrooculographic responses of right eye in horizontal recording showed the biphasic positive waveforms with a latency of 0.6 ms and an amplitude of 61.1 μV (C) when stimulating right oculomotor nerve indirectly over the dural layer at a stimulation intensity of 1 mA.

Reference

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