Balloon cells in the dentate gyrus in hippocampal sclerosis associated with non-herpetic acute limbic encephalitis

The presence of balloon cells, a pathognomonic cellular feature of focal cortical dysplasia type IIB, in a background of hippocampal sclerosis is rare. Here we report the surgical pathologic features of the hippocampus resected from a 32-year-old woman with mesial temporal lobe epilepsy and a precipitating history of non-herpetic acute limbic encephalitis. Histologically, the resected specimen showed features of hippocampal sclerosis with granule cell dispersion. Characteristically, many balloon cells, immunoreactive for nestin, vimentin, glial fibrillary acidic protein (GFAP), GFAP-delta and CD34, were observed in the molecular and granule cell layers of the dentate gyrus. In the present case hippocampal sclerosis was an apparently acquired alteration, rather than a result of maldevelopment. The appearance of balloon cells raises questions regarding their origin and morphogenesis.