Resumo
A thoracic neoplastic mass in a 6 years-old German Shepherd dog was examined. The dog had apathy, regurgitation, and ascites. A large mass occupying the cranioventral, medial and caudal mediastinum was found by X ray and ultrasonography. Grossly, a 27 x 23 x 12 cm encapsulated, multilobulated, and cystic mass was found. Firms adhesions were present between the neoplasm and the right and left cranial lung lobes. Histopathologically, the neoplastic cell population consisted of solids sheets of epithelial cells and aggregates or individual lymphocytes. By immunohistochemistry, proliferating epithelial cells were positive for keratin and lymphocytes were intensely positive for CD3, identifying them as T cells. Based on gross, histologic, and immunohistochemical findings, the neoplasm was diagnosed as a mixed thymoma.