Medial temporal lobe heterotopia as a cause of increased hippocampal and amygdaloid MRI volumes.

Magnetic resonance imaging (MRI)-based volumetric measurements of the hippocampus and amygdala are useful in detecting hippocampal and amygdaloid sclerosis in patients with temporal lobe epilepsy. In these pathological entities, volumetric MRI analysis shows the epileptogenic structures to be atrophic when compared to the normal, nonepileptogenic side. Described are 2 patients with increased hippocampal and amygdaloid volumes on the side of seizure onset due to medial temporal lobe heteroto pias. Care must be taken in the interpretation of volumetric MRI data to make certain that asymmetries in hippocampal and amygdaloid measurements are due to atrophy and sclerosis of the abnormal side and not to increased tissue such as heterotopic gray matter.