Excretory plugs from the choroid plexus in the cerebrospinal fluid of dogs with neurological disease: possible role in the formation of corpora arenacea.

Cytological specimens of cerebrospinal fluid (CSF) from 13 (6.5%) of 200 dogs with various neurological diseases contained excretory plugs (EPs) originating from choroid plexus cells (ChPCs). The presence of EPs was not related to age, breed or sex, or to any particular neurological disease. EPs, which ranged from 3 to 25 microm in diameter, had a sharp outline and contained granular material. Many such bodies were also found within ChPCs of dogs without neurological disease, which were examined to determine the origin of EPs. The results suggest that EPs found in the CSF are excretory products originating in a small population of ChPCs, and that when they reach a certain size they are eliminated into the CSF. It is possible that they serve as cores around which corpora arenacea ("brain sand") are subsequently formed.