Thymoma in a domestic rabbit.

Thymic tumors are uncommon in small domestic animals, and thymomas are infrequently reported in rabbits. This report presents a 7-year-old Netherland dwarf rabbit with an anterior mediastinal mass which caused hyperpnea, open-mouth breathing, swelling of the head, and exophthalmos. The mass was composed predominantly of lymphocytes, but the presence of thymic epithelial cells established the histologic diagnosis of thymoma.