A case of secondary somatosensory epilepsy with a left deep parietal opercular lesion: successful tumor resection using a transsubcentral gyral approach during awake surgery.

Few studies have examined the clinical characteristics of patients with lesions in the deep parietal operculum facing the sylvian fissure, the region recognized as the secondary somatosensory area (SII). Moreover, surgical approaches in this region are challenging. In this paper the authors report on a patient presenting with SII epilepsy with a tumor in the left deep parietal operculum. The patient was a 24-year-old man who suffered daily partial seizures with extremely uncomfortable dysesthesia and/or occasional pain on his right side. MRI revealed a tumor in the medial aspect of the anterior transverse parietal gyrus, surrounding the posterior insular point. Long-term video electroencephalography monitoring with scalp electrodes failed to show relevant changes to seizures. Resection with cortical and subcortical mapping under awake conditions was performed. A negative response to stimulation was observed at the subcentral gyrus during language and somatosensory tasks; thus, the transcortical approach (specifically, a transsubcentral gyral approach) was used through this region. Subcortical stimulation at the medial aspect of the anterior parietal gyrus and the posterior insula around the posterior insular point elicited strong dysesthesia and pain in his right side, similar to manifestation of his seizure. The tumor was completely removed and pathologically diagnosed as pleomorphic xanthoastrocytoma. His epilepsy disappeared without neurological deterioration postoperatively. In this case study, 3 points are clinically significant. First, the clinical manifestation of this case was quite rare, although still representative of SII epilepsy. Second, the location of the lesion made surgical removal challenging, and the transsubcentral gyral approach was useful when intraoperative mapping was performed during awake surgery. Third, intraoperative mapping demonstrated that the patient experienced pain with electrical stimulation around the posterior insular point. Thus, this report demonstrated the safe and effective use of the transsubcentral gyral approach during awake surgery to resect deep parietal opercular lesions, clarified electrophysiological characteristics in the SII area, and achieved successful tumor resection with good control of epilepsy.