Abstracts

Rationale: Identifying the primary motor (M1) and the supplementary motor area (SMA), and monitoring the pyramidal tract are important for safe resection of an epileptic focus in the medial frontal area. We aimed to establish the intraoperative SMA mapping and monitoring for patients with tumor or partial epilepsy. Methods: Four patients with a lesion in the medial frontal area were recruited in this study. All the patients underwent awake craniotomy. We put subdural grid and/or strip electrodes on the medial (1 x 6 or 2 x 8 grid) and lateral (4 x 5 grid) sides of the frontal cortex. We identified the central sulcus and the M1 of the upper and/or lower limbs by using somatosensory evoked potential and motor evoked potential (MEP). We first estimated the SMA by Cortico-Cortical Evoked Potential (CCEP) from the M1 to the medial frontal cortex ¹. We then defined the SMA by incorporating the findings of 5-train electrical stimuli (positive or negative motor response by visual inspection) under awake condition ². During the resection of the lesion, we carefully monitored the patients' motor function and sequentially recorded MEP from the M1. We off-line analyzed MEP and the silent period (SP) from the upper and lower limbs by averaging the electromyogram time-locked to stimulation. We compared the distribution of CCEPs, the motor responses 5-train produced, the MEP and SP, the area of resection and the postoperative motor outcome. Results: Large CCEPs (>25% of the maximum CCEP amplitude) and/or the evoked motor responses were identified at 4, 5, 8 and 9 electrodes on the medial frontal cortex in Patient 1 - 4 respectively. These electrodes were identified as SMA during operation. In all the patients, MEPs from the M1 were preserved throughout resection. 5-train stimulation did not provoke seizures in all. In two patients the identified SMA was partially resected, and transient SMA syndrome occurred. The intraoperative findings (CCEP and motor responses by visual inspection) and the off-line postoperative analysis (MEP and/or SP from the SMA) were concordant in 75 - 100% of the electrodes in each patient. Conclusions: This pilot study indicates that combination of and 5-train stimulation and CCEP under awake craniotomy is potentially clinically useful for intraoperative SMA monitoring. References 1. Matsumoto R, Nair DR, LaPresto E, Najm I, Bingaman W, Shibasaki H, et al: Functional connectivity in the human language system: a cortico-cortical evoked potential study. Brain 127:2316-2330, 2004. 2. Kikuchi T, Matsumoto R, Mikuni N, Yokoyama Y, Matsumoto A, Ikeda A, et al: Asymmetric bilateral effect of the supplementary motor area proper in the human motor system. Clinical Neurophysiology 123:324-334, 2012.