Interpretation and Strategy to Resolve Neuromonitoring Changes Associated With Brain Sag.

Area of Science:

• Neurosurgery
• Neurophysiology
• Medical Technology

Background:

• Intraoperative neuromonitoring (IONM) is crucial for safe maximal resection of brain tumors in eloquent areas.
• Brain sag, a shift in brain parenchyma and cortical surface, can lead to false-positive loss of sensorimotor signals during deep or large tumor resections.

Purpose of the Study:

• To describe the electrophysiological changes associated with brain sag during neurosurgery.
• To present a facile technique using saline infusion to resolve intraoperative neuromonitoring signal changes caused by brain sag.

Main Methods:

• Retrospective review of neurosurgical cases with identified intraoperative brain sag.
• Analysis of preoperative/postoperative imaging, operative details, and IONM electrophysiological traces.
• Case series presentation (6 cases) illustrating distinct electrophysiological patterns and signal restoration.

Main Results:

• Observed stepwise decreases in somatosensory-evoked potentials (SSEPs) and transcranial motor-evoked potentials (TMEPs) correlated with tumor removal or CSF loss.
• Signal changes in upper/lower extremities varied based on lesion location and head positioning, reflecting affected cortical regions.
• Saline infusion into the resection cavity or ventricle restored cortical topography and reversed false-positive IONM signal drops, indicating artifactual changes.

Conclusions:

• Brain sag is a common challenge during resection of large or deep-seated brain tumors.
• Understanding the electrophysiological signatures of brain sag is key to accurate IONM interpretation.
• The saline infusion technique effectively reverses false-positive neuromonitoring signals, enhancing IONM utility and enabling safer tumor resection.