Background-The removal of brain tumors in peri-eloquent or eloquent cortex risks causing new neurological deficits in patients. The assessment of the functionality of peri-lesional tissue is essential to avoidance of postoperative neurological morbidity. Objective-To evaluate preoperative magnetoencephalography (MEG)-based functional connectivity as a predictor of short-and medium-term neurological outcome after removal of gliomas in peri-eloquent and eloquent areas. Methods-Resting-state

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... brain MEG recordings were obtained from 79 consecutive subjects with focal brain gliomas near or within motor, sensory, or language areas. Neural activity was estimated using adaptive spatial filtering. The mean imaginary coherence between voxels in and around brain tumors was compared to contralesional voxels and used as an index of their functional connectivity with the rest of the brain. The connectivity values of the tissue resected during surgery were correlated to the early (one week post-operatively) and medium-term (six months post-operatively) neurological morbidity. Results-Patients undergoing resection of tumors with decreased functional connectivity had a 29% rate of new neurological deficit 1 week after surgery and a 0% rate at 6-month follow-up. Patients undergoing resection of tumors with increased functional connectivity had a 60% rate of new deficit at 1 week and a 25% rate at 6 months. Conclusion-MEG connectivity analysis gives a valuable preoperative evaluation of the functionality of the tissue surrounding tumors in peri-eloquent and eloquent areas. These data may be used to optimize pre-operative patient counseling and surgical strategy.