Long-term developmental outcome after early hemispherotomy for hemimegalencephaly in infants with epileptic encephalopathy

•Developmental outcome of infants with HME who underwent hemispherotomy at less than 1 year of age•All patients had a history of epileptic encephalopathy before surgery.•Patients who obtained seizure freedom after surgery showed higher postoperative developmental quotient (DQ).•Shorter seizure duration was correlated with higher postoperative DQ.•Appropriate surgery timing may facilitate additional developmental improvement.

This study aimed to identify the effect of early hemispherotomy on development in a consecutive series of 12 infants with hemimegalencephaly (HME) demonstrating epileptic encephalopathy. Mean age at onset was 20.4 days (range, 1-140), mean age at surgery was 4.3 months (range, 2-9), and mean follow-up time was 78.8 months (range, 36-121). Eleven patients had a history of early infantile epileptic encephalopathy. Vertical parasagittal hemispherotomy was performed without mortality or severe morbidities. At follow-up, seizure freedom was obtained in 8 patients (66.7%), who showed significantly higher postoperative developmental quotient (DQ) (mean, 31.3; range, 7-61) than those with seizures (mean, 5.5; range, 3-8) (p = 0.02). Within the seizure-free group, postoperative DQ correlated with preoperative seizure duration (r = − 0.811, p = 0.01). Our results showed that shorter seizure duration during early infancy could provide better postoperative DQ in infants with HME and epileptic encephalopathy.