Corticobulbar Motor Evoked Potentials for Facial and Lower Cranial Nerves: A Systematic Review of Applications and Limitations

Introduction: Corticobulbar motor evoked potentials (coMEPs), introduced in 2005, were originally proposed as an alternative to direct stimulation and free running electromyography for continuous monitoring of the facial nerve during vestibular Schwannoma surgery. The technique has since been expanded for monitoring of multiple cranial nerves (CN) across a variety of applications. This study characterizes the current state of coMEP utilization in surgery, focusing on the facial and lower CNs, to explore their applications, limitations, and potential for development.

Materials and Methods: A systematic review of all papers reporting coMEP neuromonitoring published in PubMed through December 2023 was conducted. Studies not available in English, with abstract only, and reviews were excluded. Studies were screened by two independent reviewers. Conflicts were resolved by a third reviewer. Demographic data, technical data regarding stimulation methods and parameters, and outcomes were collected. Aggregate data was analyzed to interrogate incidence, reporting variability, and diagnostic testing accuracy of the method.

Results: We identified 2,711 unique cases utilizing coMEPs, reported across 72 studies from 2005 to 2023. The majority (93%) were retrospective case reports or series (median: n = 26, range: n = 1–367). The facial nerve was the most common target (n = 41), followed by the vagus (n = 10) and hypoglossal (n = 4) nerves. 23.6% of studies analyzed multiple CNs (n = 17). Cerebellopontine angle operations (52%) were the most common application of coMEPs, followed by microvascular decompression (20%), and other skull base pathologies. Significant heterogeneity was observed in the technical application of coMEPs, including electrode type (corkscrew—86%, subdermal—11.6%, or cranial PEG-2.4%), stimulation paradigm (fixed—40.4%, or variable—59.6%), and artifact detection (double train applied—60.7%, no double train applied-39.3%). 68% of studies reported clinical outcome, while the remainder were technically focused. CoMEPS were often used alongside other neuromonitoring modalities (87.5% of studies), but performance was infrequently compared with those modalities (28.6%). About half of facial nerve studies, and 12.5% of lower CN studies reported sensitivity (range: 40–100) or specificity (range: 60–100) of coMEPs.

Discussion: CoMEPs are a powerful intraoperative tool with the potential to aid surgeons to avoid and predict postoperative neurologic dysfunction. Nonetheless, they remain an evolving technique, limited by significant variability in technical application, and therefore results. Prospective investigation is warranted to better characterize the sensitivity and specificity of coMEPs as compared with other modalities. Standardization of technique to provide consistent diagnostic accuracy will be imperative to broadening the adoption of coMEPs in skull base surgery.

 

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No conflict of interest has been declared by the author(s).

Publication History

Article published online:
07 February 2025