Epilepsy Surgery for Hemimegalencephaly: The UCLA Experience

Introduction: Hemimegalencephaly (HME) is a rare congenital brain malformation predominantly presenting with drug-resistant epilepsy, however, little is known about post-surgical outcomes. We present the largest cohort of patients with HME who have undergone surgical treatment for epilepsy.

Methods: In this retrospective observational study, patients with HME and at least one epilepsy surgery at UCLA from 1984 to 2021 were included. Patients were stratified based on Functional Hemispherectomy (FH), Anatomic Hemispherectomy (AH) or less-than-hemispheric (LTH) resection and compared in pre- and post-operative outcomes. Primary outcomes included seizure freedom, functional outcomes and operative complications based on surgical approach. Secondary analysis identified demographic, clinical, neurodiagnostic and intra-operative variables that independently predicted seizure outcomes.

Results: Among 56 patients included, 43 had FH, 8 had AH, 2 had LTH resection, 2 were non-operative, and 1 had unknown hemispherectomy type. Mean age at surgery was 23.6±31.2 months. At last follow-up, 49% of patients were seizure-free, 17 (30%) patients required ventriculoperitoneal shunt for hydrocephalus, 9/43 (21%) patients had severe developmental delay, 8/38 (21%) patients were non-verbal, and 15/38 (39%) patients were non-ambulatory. There was one intraoperative mortality due to exsanguination. Twelve (29%) required revision surgery, with 50% seizure-free post-operatively. AH compared to FH was not associated with improved seizure freedom (HR=0.48, p=0.33). However, younger age at seizure onset (HR=0.29, p=0.03), no history of EPC (HR=0.30, p=0.02) and absence of contralateral seizures on EEG (HR=0.33, p=0.04) were independent predictors of longer time-to-seizure recurrence on multivariate analysis.

Conclusion : This relatively large single-center experience demonstrates that surgery for HME remains complex, however, earlier intervention, absence of EPC and no contralateral seizures on EEG were associated with longer seizure freedom. Although a significant portion of patients required revision hemispherectomy, there was no evidence to support upfront AH. This study provides the largest HME cohort with outcomes analysis and can help guide HME treatment.