In 1987, Arai et al. first described countless foamy spheroid bodies in the degenerate substantia nigra zona reticularis in an autopsy case with narcolepsy. As the name suggests, foamy spheroid bodies are foamy spheroid structures approximately 10–50 μm in diameter that have an indistinct border and almost no affinity for H&E. Some contain relatively coarse eosinophilic granular structures. Subsequent studies have revealed that foamy spheroid bodies commonly appear in the substantia nigra zona reticularis as well as the inner segment and most ventral portion of the pallidum below the anterior commissure and develop in degenerative disease and with normal aging.
Electron microscopic tests and immunostaining have shown that foamy spheroid bodies are surrounded by astrocyte intermediate filament bundles and punctate adhesions between astrocytic processes. In addition, they contain neurofilaments; therefore, products derived from destroyed neurons are thought to be surrounded by astrocytic processes. The inner portion of these bodies is clearly stained with antiubiquitin antibodies; therefore, it is thought to contain degenerated ubiquitinated proteins. Foamy spheroid bodies can be easily missed at the first glance. However, in bodies that contain rather large, coarse, granular structures, the inner tissue appears coarse and spheroid. Consequently, they have long been mistaken for axonal swelling and dystrophic axons, in particular.