Ectopic brain tissue in the retina of a beagle dog: a case report and literature review.

Isolated ectopic brain tissue within the orbit is an extremely rare finding and has never been reported in dogs or other domestic species. In this case, a focal choristoma of ectopic grey matter-like tissue was present within the retina of a mature female beagle dog, and consisted of neurons and astrocytes as demonstrated respectively by microtubule-associated protein 2 and glial fibrillary acidic protein immunohistochemistry. The lesion was located within the optic fundus adjacent to the optic disk and surrounded by dysplastic retina. The case is presented with a review of literature on this rare entity.