Motor evoked potential monitoring during surgery of middle cerebral artery aneurysms: a cohort study.

Background: Motor evoked potential (MEP) monitoring has been widely used in brain or spine surgery to recognize potential damage of the pyramidal motor system. However, its ability to detect ischemic injury during middle cerebral artery (MCA) aneurysm surgery remains unclear. A prospective cohort study was designed to evaluate MEP changes during MCA aneurysm surgery.

Methods: From January 2009 to August 2011, 89 patients underwent MCA aneurysm surgery and were prospectively divided into 2 groups: MEP monitoring group and control group. Based on an amplitude decrement of >50% or loss, a 2-stage warning criterion of MEP changes was established. Concomitant somatosensory evoked potential changes were also recorded. MEP changes occurred in 15 patients, and various methods were used to avoid continued brain ischemia. Indocyanine green angiography and Doppler ultrasonography were performed if needed. A head computed tomography scan was performed immediately and the day after the operation.

Results: At discharge, neither motor status nor Glasgow Coma Scale score was significantly different between the 2 groups. However, at the latest follow-up (mean, 31.9 months), motor status of the patients in the monitoring group was better (P = 0.037). MEP monitoring was identified as an independent prognostic factor for motor outcome in long-term results by multivariate analysis (P = 0.042). Both wave loss and >50% amplitude decrement of MEP monitoring showed good predictive value when used as part of a 2-stage warning criterion.

Conclusions: MEP monitoring is reliable for evaluation of the ischemic status of the pyramidal motor system during MCA aneurysm surgery and can improve surgical outcomes when used appropriately.