First case report of an intrathoracal angioosteoma in a cat

Background: Angioosteoma is a benign combinatory mixed tumour, characterized by benign vascular and osseous lesions. Since then, there have been only 4 additiona human cutaneous cases reported. Objectives: The aim of the present histopathological, immunohistochemical study was to describe microscopic morphological characteristics of the intrathoracal benign combinatory mixed tumour: angioosteoma, or haemangioosteoma in a cat. Materials and Methods: An 11 year old castrated male European shorthair cat died due to multifocal linear right liver lobe ruptures with acute haemabdomen, right medial lung lobe rupture with acute haemothorax, atelectasy and acute posthaemorrhagic shock caused by car accident. During the necropsy of the carcass, in the thoracic cavity, in the precardial mediastinal area, 1 cm diameter, irregular spherical, medium red, solid tissue resistance was observed. It was separated and conserved in buffered, 8% formalin for 24 hours at room temperature, embedded in paraffin wax and further processed for sectioning (3-4 mu m) and immunohistochemistry (antibodies: anti-claudin-5, anti-CD31, anti-vimentin, anti-alpha-smooth muscle actin [SMA]). We used haematoxylin and eosin, and von Kossa-stainings for conventional histopathology. Results and Discussion: Definitive histopathological, and immunohistochemical morphological diagnosis was a intrathoracal benign combinatory mixed tumour/incidentaloma, concretely angioosteoma. Results of histopathology analysis presented a dilated cavernous vasculare channels with poorly canalized vascular tufts and scattered basophilic bony trabeculae. Endothelial cells of the haemangioma component showed intense, diffuse, homogenous, claudin-5-, and CD31-positivity. Smooth muscle cells, and pericytes of the haemangioma component were positive for SMA. All cellular components of the tumour, including neoplastic osteoma cells, spirdle cells of the haemangioma component showed diffuse, intense, homogenous vimentin-immunoreactivity. The calcified intercellular part of the osteoma component exhibited positive von Kossa staining. To our knowledge, this case is the first report of angioosteoma in domestic animal (in cat). This condition is a new entity and should be included in the differential diagnoses of benign combinatory mixed tumours, and ossifying haemangloma, or well vascularised osteoma.