Histological and topographical characteristics of canine granulomatous leptomeningitis.

Histological and topographical characteristics of granulomatous leptomeningitis were studied in 14 laboratory beagle dogs (12 males, two females), 8 to 19 months old. The dogs, which were either saline-treated controls or drug-treated animals in four different toxicity studies, remained clinically normal during the experimental period, and granulomatous leptomeningitis was identified as an incidental finding by routine histopathological examination. There were no macroscopical lesions in the brain or other organs. Microscopical lesions of the central nervous system were of three types, namely (1) a diffuse inflammatory type, characterized by diffuse infiltration of macrophages, (2) a granulomatous type, characterized by non-caseating granulomas, or (3) a fibrotic type, featuring dense connective tissue. Each of the 14 cases fell into one of three disease phases, early, fulminating and healing. In the early phase, only diffuse inflammatory-type lesions were seen. In the fulminating phase, all three types of lesion were present. In the healing phase, discrete granulomas were relatively few and fibrosis was prominent.