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Interpretation and Strategy to Resolve Neuromonitoring Changes Associated With Brain Sag
Mitali Bose1, Matthew Toczylowski1, Xiaopeng Guo2,3
1SpecialtyCare Inc., Neuro Services, Brentwood, Tennessee, USA.
Background And Objectives:
Intraoperative neuromonitoring (IONM) aides in safe maximal resection of brain tumors in eloquent areas. During the resection of large or deep-seated tumors, shifts in the peri-resectional parenchyma and cortical surface relative to cranial electrodes, or brain sag, can cause false-positive loss of sensorimotor signals. We describe patterns of electrophysiological changes associated with brain sag and a facile technique to rapidly resolve these changes intraoperatively by saline infusion.
Methods:
We reviewed cases operated on by the senior author and identified cases where brain sag was noted intraoperatively. Preoperative and postoperative imaging, operative details, and IONM electrophysiological traces were analyzed to surmise generalizable patterns.
Results:
We observe stepwise decreases in somatosensory-evoked potentials and transcranial motor-evoked potentials that occur with removal of a large intraparenchymal mass or after significant loss of cerebrospinal fluid. The pattern of upper extremity or lower extremity signal change depends on the location of the lesion and the positioning of the head, depending on which regions of the motor or somatosensory cortices are most affected by brain sag. Recovery of the somatosensory-evoked potentials and transcranial motor-evoked potentials during saline infusion into the resection cavity or ventricle, which reconstitutes the cortical topography, suggests that the IONM signal change was artifactual, rather than reflecting true physiological injury. We present 6 illustrative cases that highlight distinct patterns of electrophysiological change associated with brain sag and the extent of signal restoration.
Conclusion:
Brain sag is commonly encountered during the resection of large or deep-seated tumors. Improved understanding of the spatiotemporal electrophysiological signatures of brain sag and application of the saline infusion technique to reverse false-positive drops in neuromonitoring signals improves the utility of IONM and enhances safe resection.
Insights
Brain sag during brain tumor surgery can cause false loss of signals. Saline infusion rapidly resolves these artifactual changes, improving intraoperative neuromonitoring (IONM) utility for safe tumor resection.
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.
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