Craniopharyngioma in a dog.

Craniopharyngiomas are rare in dogs. A 3 cm suprasellar craniopharyngioma in a 13-month-old male mongrel dog is described. The mass consisted of multiple microcysts and solid areas with mesenchymal proliferation in areas of transition. Tumour cells were arranged in solid sheets or separated into islands by thick bands of collagen. Squamous differentiation of tumour cells with keratin formation and a focus of osseous metaplasia were present. Occasionally, tumour cells were arranged in rosettes. Cysts were lined by a single layer of cuboidal to low columnar epithelium and contained proteinaceous fluid with numerous cholesterol clefts. The diagnosis was based on age of occurrence, location and histological appearance.