Intraoperative electrophysiological 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 cortico-cortical evoked potential (CCEP) provoked by electrical 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 electrical 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 eight 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 four 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 the intraoperative mapping and monitoring for the MFMA by combining electrophysiological monitoring and awake craniotomy. It is clinically useful for mapping the MFMA and can prevent permanent motor deficits.