Intraoperative Electrophysiologic Mapping of Medial Frontal Motor Areas and Functional Outcomes

Objective To propose a method for intraoperative mapping and monitoring of the medial frontal motor areas (MFMA). Methods We estimated the location of the MFMA using the corticocortical evoked potential (CCEP) provoked by electric stimuli to the primary motor area (M1) of the upper limb. We localized or defined the MFMA by recording the motor evoked potentials (MEPs) provoked by electric stimuli to the medial frontal cortex around the estimated area. We monitored the patients' motor function during awake craniotomy and sequentially recorded the MEPs of the upper and/or lower limbs. This method was applied to 8 patients. Results Four patients who had part of the areas identified as the MFMA removed showed transient hemiparesis postoperatively (supplementary motor area [SMA] syndrome). The MEP from the M1 was preserved in the 4 patients. The resection of the identified MFMA might have caused their SMA syndrome. The CCEP showed a strong connection between the M1 and the SMA of the upper limb. Our method did not provoke any seizures. Conclusions This is a safe and sensitive method for intraoperative mapping and monitoring of the MFMA by combining electrophysiologic monitoring and awake craniotomy. It is clinically useful for mapping the MFMA and can prevent permanent motor deficits.