Abstracts

Rationale: EEG after disconnective hemispherectomy may show epileptiform abnormalities in the disconnected hemisphere in seizure-free patients. This report describes EEG findings in 50 patients who were seizure-free after various form of hemispherectomy procedures.

Methods: 50 consecutive patients who were seizure-free at last follow-up after hemispherectomy were identified from our epilepsy surgery database. Medical records were reviewed for clinical profile, etiology, neuroimaging findings, electrophysiological data and the EEG findings after hemispherectomy. The study was approved by Institutional Review Board.

Results: Of 50 patients, 26 were males (52%). Gliosis and encephalomalacia of various causes including perinatal stroke was the most common etiology in 35 (70%) patients. Other etiologies included: Rasmussen encephalitis in 6, malformation of cortical development in 7, and Sturge-weber syndrome in 2 patients. Thirty patients (60%) had a single seizure type, and the rest had more than one seizure type. Pre-operative EEG revealed features of epileptic encephalopathy in 12 patients (24%); 5 had hypsarrhythmia, 4 had slow spike and wave complexes, and 3 had continuous spike-waves during sleep. Age at time of surgery range from 8 months to 21 years (mean 7.5 years, median 6 years). Right hemispherectomy was performed in 23 (46%) patients. Forty-seven patients (94%) had disconnective hemispherectomy, and 3 (6%) had modified anatomical hemispherectomy. All 50 patients were seizure-free at a mean follow-up of 3.8 years (median, 3 years). Post-operative EEG showed the expected slowing and attenuation of physiological rhythms in the operated hemisphere in all patients. Epileptiform discharges exclusively in the operated hemisphere was noted in 34 patients (68%). Bilateral independent epileptiform discharges were noted in 6 patients (12%). Nine patients (18%) had no epileptiform discharges on either side and 1 (2%) had epileptiform discharges in the unoperated hemisphere only. Lateralized periodic discharges in the operated hemisphere were noted in 2 patients (4%). EEG seizures on the side of surgery without spread to the other hemisphere and without clinical signs were noted in 4 patients (8%). Thirty patients (60%) were weaned of antiseizure medications. Six (85%) of 7 patients with contralateral epileptiform discharges remained on medications at last follow up, compared to 14 (33%) of 43 without contralateral discharges.

Conclusions: The majority of patients who are seizure-free after disconnective hemispherectomy may continue to show epileptiform discharges in the operated hemisphere. Subclinical EEG seizures in the operated hemisphere may also occur in 8% of seizure-free patients. The disconnected hemisphere with intact blood supply may continue to show epileptiform discharges but be unable to cause clinical seizures after effective hemispheric disconnection. Presence of such epileptiform discharges or subclinical seizures on EEG on the operated side should not preclude tapering of antiseizure medications in seizure-free patients.

Funding: Please list any funding that was received in support of this abstract.: Source of funding: None.