Gliomatosis cerebri in six dogs.

Gliomatosis cerebri is a well-recognized entity in human medicine characterized by unusually widespread infiltration of the neuraxis by neoplastic glial cells with relative preservation of brain architecture. This report describes the pathologic features of the disease in six dogs. The dogs ranged from 3 to 9 years of age (mean 6.1 years) without evidence of breed predilection; five of the six dogs were neutered or intact males. The clinical findings were mixed (including depression, circling, cranial nerve deficits), reflecting the diffuse nature of the disease. Histologically, there was remarkably diffuse infiltration of the white and gray matter of the brain by small numbers of elongated neoplastic cells. Areas of greater cellularity formed grossly visible lesions in four cases. Anisocytosis and pleomorphism were greater in areas of higher cellularity. Other features of tumor growth included subpial accumulation, neuronal satellitosis, perivascular cuffing, and tropism for cranial nerve and brain stem nuclei. Neoplastic cells were negative on immunohistochemical stains for glial fibrillary acid protein (GFAP) and leukocyte markers, reflecting the uncertain histogenesis of these unusual neoplasms.