2026 Proffered Presentations
S296: INTRAOPERATIVE TRIGEMINAL SOMATOSENSORY EVOKED POTENTIAL MONITORING DURING SKULL BASE SURGERY
James T McMahon, MD1; Matthew Toczylowski2; Casey Jarvis, MD1; Mitali Bose2; Wenya L Bi, MD, PhD1; 1Brigham and Women's Hospital; 2Specialty Care, SpecialtyCare, Intraoperative Neuromonitoring
Background: Somatosensory evoked potentials (SSEPs) of the trigeminal nerve represent a powerful and underutilized adjunct for intraoperative neuromonitoring during skull base surgery, given the extensive pathways connected to the trigeminal nuclei. We present a single-institution retrospective review of patients with trigeminal SSEP monitoring to assess feasibility and outcome correlations.
Methods: We performed a retrospective chart review for patients undergoing craniotomy for skull base pathologies between 2022–2025 with trigeminal SSEP monitoring. Demographic, pathological, operative, and monitoring variables were abstracted. Intraoperative monitoring data included the trigeminal branches (V1–V3) recorded and any intraoperative signal change. Outcomes included new or worsened trigeminal sensory symptoms in the immediate post-operative setting and at last documented follow-up.
Results: We analyzed 67 patients (mean age 54 years, range 19–80; 45 women, 22 men) with intraoperative trigeminal SSEP monitoring. The most common pathologies and procedures were skull base meningioma of the cavernous sinus or petroclival region (n=23), trigeminal neuralgia (microvascular decompression, n=19), and large schwannomas compressing the trigeminal nerve (trigeminal: n=2, vestibular: n=9).
Of 159 branches (V1, V2, or V3) assessed, 153 had reliable SSEP signals (96%). There were 16 patients with pre-operative facial numbness; of these patients, 47/48 (98%) trigeminal branches had detectable and reliable trigeminal SSEP signals. Intraoperative signal changes were noted in 6 patients, ranging from ~30 to ~60% amplitude decrease in individual trigeminal nerve branches; three cases returned to baseline by the end of monitoring while the other three cases had partial resolution of signal change.
Out of 61 patients with no intra-operative trigeminal SSEP changes, one (1.6%) experienced new, persistent trigeminal symptoms post-operatively. This patient presented with V2 distribution numbness, and after surgery developed a broader hemifacial distribution, which has improved approximately 75% but is persistent at >6-month follow-up. Of the three out of 67 patients who experienced transient trigeminal SSEP signal change intraoperatively, with recovery to baseline by the end of the procedure, all maintained stable facial sensation post-operatively compared to prior to surgery. In the three patients with trigeminal SSEPs signal decrease compared to baseline at the end of surgery, one had no new sensory changes, while two (66.6%) experienced worsened hemifacial numbness which remained present at 6 months after surgery.
Conclusions: Trigeminal SSEPs were successfully monitored in a series of diverse skull base procedures, even in patients with pre-operative numbness. The presence of stable intra-operative signals was highly predictive of no persistent trigeminal deficits on follow-up. In contrast, a drop in signal amplitude without return to baseline harbingers long-standing facial numbness. These preliminary findings support further study of branch-specific monitoring thresholds and their potential predictive value for postoperative outcomes.