Thymoma in two ferrets.

A cranial mediastinal mass was observed radiographically in two 5-year-old adult male ferrets (Mustela putorius furo), both with histories of chronic episodic vomiting, dyspnea, and lethargy. Malignant lymphoma, a common neoplasm observed in ferrets, was considered the most likely diagnosis. Cardiomegaly and splenomegaly were also present. Histologically both mediastinal masses were composed of thymic epithelial cells and small lymphocytes, establishing a diagnosis of thymoma. Thymoma should now be included in the differential diagnosis of a cranial mediastinal mass in ferrets.