Cerebral granular cell tumor (myoblastoma) in a dog: case report and literature review.

An infiltrative granular cell tumor (myoblastoma) occurred in the superficial parieto-occipital cortex of an ataxic 12-year-old dog. The neoplasm was characterized by cells with numerous small PAS-positive, diastase-resistant cytoplasmic granules. The neoplasm also had numerous cells with large globular PAS-positive bodies (angulate bodies). Ultrastructurally, the neoplastic cells were characterized by numerous homogenous electron-dense, sharply bounded granules and large pleomorphic, indistinctly bounded granules. The angulate bodies were composed of 8- to 10-nm fibrils, a few of which formed parallel arrays or tubule-like structures. This represents the first report of a granular cell tumor in the central nervous system of the dog.