Suprasellar germ cell tumors in the dog: a report of five cases and review of the literature.

Suprasellar germ cell tumors were identified in five young adult to middle-aged dogs. Clinical signs included depression, mydriasis, ptosis and visual deficit. At necropsy large extramedullary masses were found on the ventral surface of the rostral brain stem. Histologically four were characterized by sheets and nests of moderately pleomorphic round cells resembling seminoma, admixed with larger vacuolated cells, glandular formations with secretory material, and occasional foci of squamous differentiation. The fifth case was more homogeneous, with germinomatous elements predominating. Immunohistochemical examination of three tumors revealed positive staining for alpha fetoprotein. Although only one case showed intracranial metastasis, these tumors were considered malignant due to the marked local invasion and destruction. The veterinary literature is reviewed, and we propose that two tumors previously reported as craniopharyngioma be reclassified as germ cell tumors. One other tumor previously reported as an unclassified suprasellar tumor was identified, which also demonstrated features of a germ cell tumor.