Fine-structure of bilateral radionecrosis in the dorsal hippocampus.

Abstract

The data with which this paper deals were obtained from white rats receiving limited head X-irradiation, tested for behavioral changes, and sacrificed for light and electron microscopic evaluation 1 year after the irradiation. No evidence was found for a general loss or change in cortical or subcortical neurons. On the other hand, there was bilateral focal degeneration in the fimbria of the fornix in the dorsal hippocampus. This involved considerable numbers of pyramidal and granule cells, presumably secondary to delayed vascular changes. Widespread hypertrophy of astrocytes was noted throughout the irradiated zone. Within each central necrotic zone invasive collagen, reticulin and fibrin were present. In general, blood vessels showed only occasional evidence of thickening. However, the blood vessels in the areas of frank necrosis in the fimbria and internal capsule exhibited intense thickening leading to hyalinization.