Cerebral lipoma and the underlying cortex of the temporal lobe: pathological features associated with the malformation.

Intracranial lipomas are believed to be congenital malformations rather than true neoplasms, resulting from the abnormal differentiation of the meninx primitiva, the undifferentiated mesenchyme. We report here the surgical pathological features of a lipoma that was located on the cerebral surface of an abnormally formed fissure, and the underlying cortex of the middle temporal gyrus of a 20-year-old woman. The mass was composed of typical adipose tissue in which a large number of blood vessels were present. Thick connective tissue associated with the arachnoid membrane covered the cortical surface. The cortex exhibited a polymicrogyric configuration in which the cortical ribbon was abnormally undulated and excessively folded. Reelin-immunolabeled Cajal-Retzius-cell-like cells were observed frequently in the fused molecular layer. The cortical lamination underlying the molecular layer was poorly defined. Along the border between the connective tissue and cortical surface, there was a narrow zone in which the mesenchymal and neuronal tissues were intermingled, and where immunohistochemical and ultrastructural investigations disclosed disruption of the basal lamina, prominent astrocytosis, and abundant axonal and synaptic profiles. These findings suggest that focal disturbances in cerebral cortical development occur in association with the development of lipomas.