Intraoperative electrical stimulation of the cortex reveals the speech area missed by extraoperative stimulation because of epicortical hematoma.

Abstract

Dear Editor, Invasive EEG evaluation is a well-established procedure to individually plan resective epilepsy surgery if the epileptogenic zone is near the eloquent cortex. Electrical stimulation of the cortex is used to identify the eloquent cortex and delineate the resection boundaries. This can be done either intraoperatively or extraoperatively [4]. Reliable results of the stimulation are important to avoid postoperative neurologic deficits. We report on a patient in whom extraoperative stimulation revealed false-negative results. Intraoperative electrical simulation helped to avoid neurological postoperative deficits by identifying the localization of the speech area. This 26-year-old right-handed female had suffered from drug-resistant frontal lobe epilepsy secondary to histologically proven cortical malformation since the age of 10. Her almost daily seizures were characterized by either psychic auras of sudden fear followed by complex, mainly proximal motor activity (hyperkinetic) or, less commonly, she had aphasic seizures followed by loss of consciousness (dialeptic seizure) [1]. Three-Tesla magnetic resonance imaging (MRI), including 1-mm T1-weighted and FLAIR acquisition, did not reveal the cortical malformation, which was documented histologically. She was considered a candidate for resective epilepsy surgery and underwent noninvasive EEG monitoring, which revealed interictal epileptiform discharges, mainly left frontal and to a lesser extent right fronto-central. Ictal EEG showed either left frontal or frontal non-lateralized seizure patterns associated with her habitual seizures. Invasive EEG videomonitoring was subsequently carried out with a subdural grid and strips covering the left lateral, medial and orbital frontal lobe. Implantation of electrodes was unremarkable without any hemorrhagic complications. The postoperative computer tomography (CT) scan was unremarkable except for the artifacts from the implanted platinum-iridium electrodes. No subdural hematoma was seen. The invasive evaluation confirmed a widespread seizure onset zone in the left frontal region covered by the electrodes. Extraoperative electrical stimulation of the electrodes failed to identify any speech-related function. Therefore, intraoperative stimulation was planned. Recraniotomy for electrode removal and resection revealed an epicortical 3-mm-thick hematoma underneath the inferior frontal subdural electrode grid (Fig. 1) [3]. At this point, it was obvious that the resection could not rely on the extraoperative stimulation. The detailed intraoperative electrical stimulation of this region revealed speech function in the left inferior frontal gyrus (Fig. 1). The subsequent resection included the superior and middle frontal gyrus, sparing the speech area in the inferior frontal gyrus. Postoperatively, the patient had no speech deficit and has remained seizure free for 7 years now. Reliable localization of the eloquent cortex is crucial for delineation of resection boundaries in epilepsy surgery to avoid postoperative speech deficits [2]. False-negative results contribute partially to postoperative speech deficits [2]. Epiand subdural hematomas are well-known complications of subdural grid electrode evaluations [3, 5]. The risk of * Soheyl Noachtar noa@med.uni-muenchen.de