An EEG Study of Patients with Unilateral Diffuse Cortical Dysplasia Who Underwent Hemispherectomy

Abstract

Purpose: Functional hemispherectomy was performed for patients with intractable epilepsy with unilateral diffuse cortical dysplasia. We retrospectively studied interictal scalp EEGs recorded both preoperatively and postoperatively. Methods: The cases were 12 (six male and six female) patients who had been definitively diagnosed as having unilateral cortical dysplasia by both neuropathologic and neuroradiologic findings. Five patients exhibited diffuse cortical dysplasia, and the other seven exhibited hemimegalencephaly. Their interictal scalp EEGs were classified into four groups based on the appearance of abnormal epileptiform discharges. The groups were focal, unilateral, bilaterally synchronous, and bilaterally nonsynchronous. We discussed the type of EEG, the magnetic resonance imaging (MRI) findings, and postoperative prognosis. Postoperative prognosis was made according to Engel's classification. The operation was functional hemispherectomy by disconnection. Results: The age at the time of the operation was from 5 months to 8 years and 6 months. The mean age was 3 years and 8 months. The age at the onset of the first seizure was from 0 days to 1 year and 8 months. All patients had frequent partial motor seizures caused by the affected side of the brain. Eight patients were associated with secondarily generalized seizures, and two were associated with drop attacks. All cases had various degrees of hemiparesis caused by the affected brain. The patients with hemimegalencephaly had more frequent attacks, resulting in epilepsia partialis continua in three cases. It was also striking that the onset time of the first seizure in these patients tended to be earlier than that in the patients with diffuse cortical dysplasia. The EEGs were classified as (1) in two cases, (2) in one case, (3) in five cases, and (4) in four cases. All patients, including even EEG types (3) and (4). became seizure free after the operation. Two patients were able to discontinue their antiepileptic medication. After functional hemispherectomy, even in a seizure‐free state, abnormal epileptic discharges remained in 10 patients on the affected side of the brain. Conclusions: We clarified the importance of the global assessment encompassing ictal symptoms, neuroradiologic findings, and EEG classification before the operation. The operative outcome was very excellent regardless of whether the EEG showed a unilateral or bilateral epileptiform discharge pattern. We concluded that the EEG type was not a conclusive factor. As stated previously, type (3) and (4) EEGs did not contraindicate hemispherectomy. Postoperative active epileptic discharges from the affected side of the brain indicated a viable state of the disconnected brain and are not related to the surgical outcome.