Tag: Intraoperative neurophysiological monitoring

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Electrophysiological monitoring of trigeminal nerve sensory root using sensory-masseter response for microvascular decompression in trigeminal neuralgia

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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Petrosal Meningiomas: Factors Affecting Outcome and the Role of Intraoperative Multimodal Assistance to Microsurgery

Neurosurgery, Volume 84, Issue 6, June 2019, Pages 1313–1324

Petrous meningiomas (PMs) represent a subset of posterior fossa tumors accounting for ∼8% of all intracranial meningiomas. Surgical treatment of PMs is challenging because of their relationships with vital neurovascular structures of the cerebellopontine angle.

OBJECTIVE: To investigate independent pre- and intraoperative predictors of PM surgery outcome.

METHODS:We reviewed the surgical and outcome data of patients who underwent microsurgical resection of PMs from 1997 to 2016. From 2007 onward, a multimodal intraoperative protocol consisting of intraoperative neuromonitoring (IONM), endoscopy, and indocyanine green (ICG) videoangiography was applied. Outcome variables included extent of resection, Karnofsky performance status (KPS), overall survival, and progression-free survival (PFS).

RESULTS: A total of 54 patients were included. Independent predictors of gross total resection (GTR) included retromeatal location (P < .0175; odds ratio [OR] 4.05), absence of brainstem compression (P < .02; OR 3.55), and histological WHO grade I (P < .001; OR 3.47). Nongiant size (P < .012; OR 4.38), and WHO grade I (P < .0001; OR 7.7) were independent predictors of stable or improved KPS. The use of multimodal intraoperative tools to assist surgery independently predicted GTR (P < .002; OR 6.8) and good KPS (P < .018; OR 4.23). Nongiant size (P = .01) and WHO grade I (P = .002) were significantly associated with increased PFS.

CONCLUSION: Notwithstanding the limitations of a retrospective study, our results suggest that support of microsurgery by a combination of IONM, endoscopy, and ICG videoangiography may improve patient outcome in PM surgery.

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The value of multimodality intraoperative neurophysiological monitoring in treating pediatric Chiari malformation type I

CMI

Acta Neurochir (2016) 158:335–340

Chiari malformation type I is defined as a descent of cerebellar tonsils below the level of the foramen magnum. The traditional treatment for symptomatic patients is foramen magnum decompression (FMD) surgery. Intraoperative neurophysiological monitoring (INM) is an established surgical adjunct, which is proposed to reduce the potential risk of various surgical procedures. Though INM has been suggested as being helpful in patient positioning and in determining the optimal surgical extent of FMD (i.e., duroplasty, laminectomy, tonsillectomy), its shortcomings include prolongation of anesthesia and surgery as well as monetary costs. Multimodality INM including transcranial-electric motor evoked potential (TcMEP) is not routinely employed in most practices. This study evaluates efficacy of multimodality INM during FMD.

Methods This work is a retrospective analysis of prospectively collected data. Twenty-two FMD surgeries in 21 pediatric patients (aged 1–18 years) were performed at our center utilizing multimodality INM. All patients presented Chiari malformation type I, 18 of which had presented with syringomyelia, underwent posterior fossa decompression (FMD+ C1 laminectomy), accompanied in some with additional cervical laminectomies, duroplasty, and partial tonsillectomies. TcMEP and somatosensory evoked potentials (SSEP) were monitored throughout the procedure including before and after positioning. INM alarms were correlated with perioperative and long-term patient outcomes.

Results INM data remained stable during 19 operations. Three cases displayed significant attenuation in the monitoring signals, all concomitant with patient positioning on the surgical table. One case showed attenuation in SSEP data only, which remained attenuated following repositioning. Another displayed altered TcMEP concomitant with positioning which partially stabilized following repositioning and resolved following bony decompression. The third case showed unilateral attenuation of both TcMEP and SSEP data, which did not rectify until closure. In each of these three cases, no new neurological deficits were observed post operatively.

Conclusions Multimodality INM can be useful in FMD surgery, particularly during patient positioning. TcMEP attenuations may occur independent of SSEPs. The clinical implications of these monitoring alerts have yet to be defined. There is a need to establish an optimal, cost-effective monitoring protocol for FMD.

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