Acta Neurochirurgica (2026) 168:13
This study presents a novel intraoperative electrophysiological technique—the sensory-masseter response (SMR)—for localizing neurovascular compression (NVC) during microvascular decompression (MVD) for trigeminal neuralgia. In 34 patients, SMR was recorded in 82.4% and showed strong spatial correlation with intraoperatively identified NVC, with significantly lower stimulation thresholds at compression sites (median 0.3 mA).
The authors describe methodology, threshold analyses, mechanistic hypotheses linking focal demyelination and sensory-motor anastomoses to SMR, illustrative cases, safety considerations, and limitations. They conclude SMR offers high spatial specificity as a potential real-time adjunct for MVD, but recommend larger studies to validate clinical utility.
Sensory-Masseter Response (SMR) Technique: SMR is a novel intraoperative electrophysiological monitoring method that applies microcurrent stimulation to the intracranial trigeminal sensory root and records compound muscle action potentials (CMAPs) from the masseter muscle to localize neurovascular compression (NVC) during microvascular decompression (MVD) for trigeminal neuralgia (TN).
High Spatial Specificity and Correlation with NVC: SMR was successfully recorded in 82.4% of cases (28/34), with a strong spatial correlation between SMR-positive sites and intraoperatively identified NVC (p < 0.001).
Lower Stimulation Threshold at NVC Sites: The stimulation threshold required to elicit SMR was significantly lower at NVC sites (median 0.3 mA, IQR 0.2–0.4 mA) compared to distal, central, or non-compressed segments, indicating localized neural hyperexcitability likely due to demyelination.
Mechanistic Basis—Sensory-Motor Root Anastomoses: SMR is likely mediated by abnormal anastomotic pathways between the trigeminal sensory and motor roots at the NVC site, enabling direct excitation of the masseter muscle and bypassing the central reflex arc.
Clinical Utility and Limitations: SMR provides real-time functional feedback for intraoperative localization of NVC, but its clinical value and influence on surgical outcomes require further validation in larger, controlled studies.
Potential Pathogenic Insight: The ability to elicit SMR at NVC sites supports the hypothesis that focal demyelination and abnormal sensory-motor conduction contribute to TN pathogenesis and characteristic symptoms like chewing-triggered pain.
Safety Considerations: SMR stimulation can cause transient blood pressure elevation due to sympathetic activation; precautions include deepening anesthesia and monitoring hemodynamics during stimulation.
Study Limitations: The main limitations include small sample size, absence of SMR testing in non-TN or healthy controls, possible technical constraints in nerve exposure, and restriction of recordings to the masseter muscle only.
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