Contralateral MRI abnormalities in candidates for hemispherectomy for refractory epilepsy

P>Purpose: To assess the impact of contralateral magnetic resonance imaging (MRI) findings on seizure outcome after hemispherectomy for refractory epilepsy. Methods: We retrospectively reviewed 110 children, 0.4-18 (median 5.9) years of age, who underwent hemispherectomy for severe refractory epilepsy at Cleveland Clinic Children's Hospital. In children with contralateral (as well as ipsilateral) MRI findings appreciated preoperatively, the decision to proceed to surgery was based on other features concordant with the side with the most severe MRI abnormality, including ipsilateral epileptiform discharges, lateralizing seizure semiology, and side of hemiparesis. Results: We retrospectively observed contralateral MRI abnormalities (predominantly small hemisphere, white matter loss or abnormal signal, or sulcation abnormalities) in 81 patients (74%), including 31 of 43 (72%) with malformations of cortical development (MCD), 31 of 42 (73%) with perinatal injury from infarction or hypoxia, and 15 of 25 (60%) with Rasmussen's encephalitis, Sturge-Weber syndrome, or posttraumatic encephalomalacia. Among 84 children (76%) with lesions that were congenital or acquired pre- or perinatally, 67 (83%) had contralateral MRI abnormalities (p = 0.02). Contralateral findings were subjectively judged to be mild or moderate in 70 (86%). At follow-up 12-84 (median 24) months after surgery, 79% of patients with contralateral MRI abnormalities were seizure-free compared to 83% of patients without contralateral MRI findings, with no differences based on etiology group or type or severity of contralateral MRI abnormality. Discussion: MRI abnormalities, usually mild to moderate in severity, were seen in the contralateral hemisphere in the majority of children who underwent hemispherectomy for refractory epilepsy due to various etiologies, especially those that were congenital or early acquired. The contralateral MRI findings, always much less prominent than those in the ipsilateral hemisphere, did not correlate with seizure outcome and may not contraindicate hemispherectomy in otherwise favorable candidates.