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Somatosensory Evoked Potential Monitoring During Endoscopic Endonasal Approach to Skull Base Surgery: Analysis of Observed Changes

Thirumala, Parthasarathy D MD, MS*‡; Kassasm, Amin B MD§; Habeych, Miguel MD*; Wichman, Kelley BS¶; Chang, Yue-Fang PhD*; Gardner, Paul MD*; Prevedello, Daniel MD‖; Snyderman, Carl MD*#; Carrau, Ricardo MD**; Crammond, Donald J PhD*; Balzer, Jeffrey PhD*¶

doi: 10.1227/NEU.0b013e31821606e4
Operative Technique

BACKGROUND: Intraoperative neurophysiological monitoring, including upper- and lower-extremity somatosensory evoked potentials (SSEPs), has been used to identify and prevent injury to neurovascular structures during conventional skull base surgery. The expanded endonasal approach (EEA) is a novel minimally invasive approach to skull base surgery. However, it carries the risk of injury to neurovascular structures, including the internal carotid artery, anterior cerebral artery, and cranial nerves.

OBJECTIVE: To evaluate the value of SSEP monitoring to predict and/or prevent neurovascular deficits during EEA to skull base surgery.

METHODS: We retrospectively identified 999 consecutive patients who had intraoperative neurophysiological monitoring during EEA skull base surgery at our institution. A total of 976 patients had SSEP monitoring and a documented postoperative neurological examination.

RESULTS: The incidence of changes in SSEP during the procedure was 20 of 976 (2%). The incidence of new postoperative neurological deficits was 5 of 976 (0.5%). The positive and negative predictive values of SSEPs during EEA to predict neurovascular deficits were 80.00% and 99.79%, respectively.

CONCLUSION: Intraoperative SSEP monitoring was able to identify impending risk to neurovascular structures to prevent permanent postoperative neurological deficits. We advocate a comprehensive approach to neurophysiological monitoring during EEAs, including SSEPs, spontaneous and triggered electromyography of the cranial nerves III through XII, brainstem auditory evoked potentials, and electroencephalogram, depending on the surgical approach and location of the neural structures at risk.

*Department of Neurological Surgery and ‡Department of Neurology, University of Pittsburgh, Pittsburgh, Pennsylvania; §The Chan Soon-Shiong Neuroscience Institute and the John Wayne Cancer Institute at St. John Health Center, Santa Monica, California; ¶Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; ‖Department of Neurological Surgery, The Ohio State University, Columbus, Ohio; #Department of Otolaryngology, University of Pittsburgh, Pittsburgh, Pennsylvania; **Department of Otolaryngology, The Ohio State University, Columbus, Ohio

Received, May 25, 2010.

Accepted, January 4, 2011.

Published Online, March 15, 2011.

Correspondence: Parthasarathy D. Thirumala, MD, MS, Center for Clinical Neurophysiology, Department of Neurological Surgery, UPMC Presbyterian, Ste B-400, 200 Lothrop St, Pittsburgh, PA 15213. E-mail:

Copyright © by the Congress of Neurological Surgeons