HEMIMEGALENCEPHALY - MORPHOLOGICAL AND IMMUNOCYTOCHEMICAL STUDY

Hemimegalencephaly (HME), a rare congenital abnormality characterized by unilateral enlargement of the cerebral hemisphere, is one of the le ss common causes of intractable seizures. We report a 6-month-old infa nt with uncontrolled seizures who was diagnosed to have a large mass l esion based on a CT scan. Postmortem examination revealed left-sided H ME with pachygyria, widened cortex, indistinct grey-white junction, an d distorted deep nuclear masses. Histological features included loss o f cortical lamination, large atypical neurons with argyrophilic accumu lations, ballooned cells, neuronal heterotopia, and astrocytosis with dystrophic calcification. The heterotopic neurons in the white matter were present in a radial pattern suggestive of aberrant neuronal migra tion. Several large neurons were dystrophic with cytoskeletal abnormal ities like phosphorylated high molecular weight neurofilament and ubiq uitin in the cytoplasm. However, typical neurofibrillary tangles with Congo red and tau positivity were not observed. Synaptophysin labellin g was found to be decreased in the cortex, but some of the abnormal ne urons had dense perisomatic label. The majority of the balloon cells w ere astrocytic in origin, being positive for glial fibrillary acidic p rotein and negative for the neuronal markers. Although the etiology of HME is not known, it provides an opportunity to study anomalous devel opment of the brain and neuronal developmental abnormalities.