Thymic cavernous haemangioma in a dog.

A 12-year-old male neutered Australian Shepherd Dog was presented to Charlotte Animal Referral & Emergency with a history of a thoracic mass. On physical examination, physiological parameters were within the normal ranges, and a complete haemogram and serum biochemistry profile were unremarkable except for mild thrombocytopenia. A computed tomography scan revealed a 21 × 15 × 12.7 cm thoracic mass encompassing the cranial mediastinum and extending to the right caudal thorax. The mass was surgically removed and histopathological evaluation revealed that it comprised remnants of the thymus and a neoplasm composed of large blood-filled vascular spaces lined by a single layer of endothelial cells with mild anisocytosis and anisokaryosis. The neoplastic cells had diffuse strong immunolabeling for endothelial cell marker CD31. Multifocally, there were large cystic degenerated areas of thymic tissue lined by plump cytokeratin AE1/AE3-positive epithelial cells. Based on these findings, a diagnosis of thymic cavernous haemangioma (CH) was made. Thymic CH is rare in animals, with the only reported case in a cross bred cow. To our knowledge, this is the first case of a thymic CH in a dog.