Intraoperative neurophysiological monitoring for motor function preservation during AVMs resection: Indication or redundancy? Beyond the doctrine of “all-or-nothing”

TL;DR

This study shows that using real-time brain monitoring during surgery helps preserve motor function when removing brain malformations in sensitive areas.

Contribution

The study demonstrates that intraoperative neurophysiological monitoring can safely enable resection of motor-eloquent AVMs without new motor deficits.

Findings

IONM allowed safe resection of AVMs in motor-eloquent areas without new motor deficits in 48 patients.

Preoperative modified Rankin Scale was a stronger predictor of outcome than motor eloquence in ruptured AVMs.

No significant difference in motor outcomes was found between high- and low-risk AVM groups using IONM.

Abstract

The resection of cerebral arteriovenous malformations (AVMs) involving eloquent motor regions remains one of the most challenging tasks in neurosurgery due to the risk of irreversible motor deficits. Historically, such lesions have often been managed conservatively or with radiosurgery, particularly when located near primary motor cortex or corticospinal tracts. However, the advent of intraoperative neurophysiological monitoring (IONM) allows for real-time feedback on motor pathway function, potentially enabling safer resections in areas previously considered inoperable. This study investigates the effectiveness of IONM in reducing motor morbidity during AVM surgery. We prospectively enrolled 48 patients who underwent AVM resection between 2018 and 2025 at a single center. All surgeries incorporated a standardized IONM protocol, including continuous somatosensory evoked potentials (SSEPs), motor evoked potentials (MEPs), and dynamic cortical and subcortical mapping. Patients were stratified into high and low motor-risk groups based on AVM topography. Clinical, imaging, and angioarchitectural data were analyzed. Primary outcomes were new postoperative motor deficits; secondary outcomes included modified Rankin Scale (mRS) scores and residual nidus presence. Statistical analysis included univariate and multivariate regression. Of the 48 patients (mean age 45.2), 42% presented with hemorrhage and 50% had left-hemisphere AVMs. Spetzler-Martin grades ranged from I to IV. Three patients (6.25%) had residual AVM postoperatively, two of which were intentional due to IONM alerts. None developed new deficits. One residual spontaneously thrombosed during follow-up. Multivariate analysis showed preoperative mRS, not motor eloquence, was the main predictor of outcome in ruptured AVMs. No significant difference in postoperative motor function or mRS was found between high- and low-risk groups. IONM enables safe, function-preserving AVM resection in motor eloquent areas. It supports intraoperative decision-making, reducing morbidity and expanding surgical indications guiding a “maximal safe resection” strategy focused on functional preservation rather than angiographic radicality alone.

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