Optimization of direct cortical stimulation using tibial versus median nerve sensory mapping during midline brain tumor resection: illustrative case.

BACKGROUND: During brain tumor resection, neurophysiological mapping and monitoring help surgeons locate, characterize, and functionally assess eloquent brain areas in real time. The selection of mapping and monitoring targets has implications for successful surgery. Here, the authors compare direct cortical stimulation (DCS) as suggested by median nerve (MN) with posterior tibial nerve (PTN) cortical sensory mapping (SM) during mesial lesion resection.

OBSERVATIONS: Recordings from a 6-contact cortical strip served to generate an MN and a PTN sensory map, which indicated the strip was anterior to the central sulcus. Responses exhibited an amplitude gradient with no phase reversal (PR). DCS, elicited through a stimulus probe or contact(s) of the strip, yielded larger responses from the corresponding sensory mapped limb; that is, PTN SM resulted in larger lower limb muscle responses than those suggested by MN SM.

LESSONS: SM of the MN and PTN is effective for localizing eloquent cortical areas wherein the PTN is favored in surgery for mesial cortical tumors. The recorded amplitude of the cortical somatosensory evoked potential is a valuable criterion for defining the optimal location for DCS, despite an absent PR. The pathway at risk dictates the specifics of SM, which subsequently defines the optimal location for DCS.