Abstracts

Rationale: To assess the impact of contralateral MRI findings on postsurgical seizure outcome in a large cohort of children who underwent hemispherectomy for refractory epilepsy due to hemispheric malformations of cortical development (MCD), infarction, perinatal intraventricular hemorrhage (IVH) and hypoxic ischemic injury, Rasmussen’s encephalitis, Sturge Weber syndrome or traumatic head injury.Methods: From our pediatric epilepsy surgery database, we identified 127 children, 0.4 to 18 (median 5.7) years of age, who underwent hemispherectomy at the Cleveland Clinic Children’s Hospital between 1996 and 2006. All patients had severe refractory epilepsy with mental handicap, hemiparesis, and an epileptogenic lesion on brain MRI. When additional abnormalities on the contralateral MRI were appreciated preoperatively, the decision to proceed to surgery was based on the more pronounced nature of the lesion on the side consistent with hemiparesis; lateralizing findings on EEG and seizure semiology; and severity of the epilepsy. MRIs were blindly reviewed by two epileptologists and a neuroradiologist for findings ipsilateral and contralateral to the side of surgery, and findings were compared with seizure outcome at 12 to 84 (median 24) months after surgery. Results: We observed contralateral abnormalities on preoperative MRI in 81 patients (74%). These findings were always less prominent than on the side of surgery. The most common contralateral findings in patients with MCD (31/43 patients, 72%) were small hemisphere (13, 42%), white matter loss (11, 35%), abnormal white matter signal (14, 42%), and sulcation abnormalities (12, 39%). The most common contralateral findings in patients with infarction or perinatal IVH and hypoxic ischemic injury (35/42, 83%), Rasmussen’s encephalitis (8/17, 47%), Sturge Weber syndrome (4/4, 100%), or trauma (3/4, 75%) were white matter loss (34, 51%) and abnormal white matter signal (41, 61%). Overall, 83% of patients without contralateral findings were seizure free at follow up compared to 80% of patients with contralateral as well as ipsilateral abnormalities on MRI, with no differences in seizure outcome between etiology groups or type of contralateral MRI abnormality.Conclusions: MRI abnormalities in the contralateral hemisphere were seen in the majority of children who underwent hemispherectomy for refractory epilepsy due to a variety of etiologies. These findings, always less prominent than those in the ipsilateral hemisphere, did not correlate with seizure outcome and may not contraindicate hemispherectomy in selected children.