Hemimegaloencephaly with periventricular heterotopia--case report.

A 7-year-old girl was admitted with an unusual anomaly of hemimegaloencephaly associated with periventricular heterotopia manifesting as intractable seizures and mental retardation. Magnetic resonance (MR) imaging showed left hemispheric hypertrophy and left ventricular dilatation. Proton density-weighted MR imaging revealed a periventricular lesion isointense with gray matter. MR imaging is an effective method for diagnosing hemimegaloencephaly and heterotopia.