Bilateral neuropathologic changes in a child with hemimegalencephaly.

Evaluation of a 7-month-old girl with developmental delay and intractable seizures revealed hemispheric asymmetry and an enlarged right cerebral hemisphere. Because of a history of seizures refractory to medical therapy, she was admitted for right hemispherectomy, but died of complications of surgery. Postmortem brain examination revealed asymmetric enlargement of the right cerebral hemisphere but no gross abnormalities in the left hemisphere. Microscopic examination demonstrated bilateral neuropathologic changes consistent with severe cortical dysplasia in the right cerebral hemisphere and mild cortical dysplasia in the left. Although white matter abnormalities in the unaffected hemisphere have been reported in hemimegalencephaly, bilateral cortical abnormalities, not reported previously in patients with hemimegalencephaly, may account for the varied clinical outcome with medical therapy or after hemispherectomy.