Abstracts

Rationale: Functional hemispherectomy is a surgical procedure used for the relief of medically intractable epilepsy in children with hemispheric lesions. This study aimed to assess the prognostic factors for postoperative seizure outcome after hemispherectomy. Methods: Twenty patients with medically intractable epilepsy secondary to hemispheric lesion underwent functional hemispherectomy between 2003 and 2010. Median age at seizure onset and median epilepsy duration were 13 months (2 days -5 years) and 3.7 years (11 months-11 years) respectively. The etiology included 12 cases of malformation of cortical development including 8 focal cortical dysplasia, 2 hemimegalencephaly, and 2 schizencephaly, 4 perinatal strokes, 2 Rasmussen encephalitis, and 2 traumatic brain injury. The data from multimodal presurgical studies including clinical seizure semiology, localization of epileptiform abnormalities on the long-term scalp EEGs (20/20), both structural and functional neuroimagings such as Bain MRI(20/20), FDG PET scan (11/20), interictal/ictal SPECT scans (4/20) and Magnetoencephalography (MEG, 4/20) were reviewed. All study results were concordant to the hemispherectomy side, except only one ictal EEG. One patient who had class IB outcome postoperatively had ictal EEG onset in the contralateral hemisphere (false lateralization). One patient lost follow up after surgery. Seven patients had intracranial EEG monitoring. Five had repeat operations after initial lesionectomy (n=3) or Grid-based surgery (n=2), The median follow-up duration was 2 years (1 month-7.6years). Seventeen patients (89.5%) had favorable postoperative seizure outcome (11 Engel class Ia, 4 Ib, 2 II). Two patients had Engel class IVB outcome. The seizure onset age, epilepsy duration or presence of FCD were compared between group with class I outcome and group with class II, III, IV outcome. The extent of completeness of disconnection was determined by blinded review of post operative MRI studies. The relationship between postoperative seizure outcome and presence of incomplete disconnection were compared using Fisher's exact test. Results: Among 19 patients, there was no difference in seizure onset age, epilepsy duration or presence of FCD between group with class I outcome and group with class II, III, IV outcome (p > 0.05). In 14 patients (70%), the postoperative brain MRIs were available for the retrospective review. Six had complete disconnection and eight had incomplete disconnection in splenium of corpus callosum. There was no significant difference in seizure outcome between complete versus incomplete disconnection in splenium of corpus callosum (p>0.05).Conclusions: Most patients (89.5%) undergoing functional hemispherectomy demonstrate favorable postoperative seizure outcome regardless of the extent of disconnection of the splenium of the corpus callosum.