Detection and characterization of chondroid metaplasia in canine atrioventricular valves.

The atrioventricular valves of 25 dogs of different breeds and age were examined grossly and microscopically following histochemical staining and immunohistochemical labelling for collagen types I, III and VI, and for fibronectin and laminin. Foci of cartilage were identified in the tricuspid septal leaflet within the fibrosa (n=21) or spongiosa (n=3). These were further characterized as either fibrocartilage, predominantly composed of collagens I and VI, or hyaline cartilage consisting of laminin and collagens III and VI. Eighteen of the dogs were of large breed and seven of small breed. Retrospective echocardiographic findings were available from five cases and in three of these a hyperechogenic structure was identified corresponding to the cartilage focus (0.1, 1.12 and 5.63 mm(2) in size). The clinical significance and mechanism of formation of these cartilaginous foci remain undetermined, although factors such as breed, size and concurrent chronic valvular disease may be significant.

Primary and secondary heart tumours in dogs and cats.

Primary and secondary neoplasms of the canine and feline heart are uncommon. During a 2-year period, 83 dogs suffering from primary cardiac (n=11), extracardiac benign (n=6) or malignant (n=66) tumours and 30 cats with primary cardiac (n=1) or extracardiac (n=29) malignant tumours were examined. Echocardiography revealed four cases of primary cardiac neoplasms in dogs, but secondary heart tumours were not detected. After necropsy, tissue samples from the heart and tumours were examined histologically and immunohistochemically. In dogs, primary neoplasms included seven haemangiosarcomas, two chemodectomas, one rhabdomyosarcoma, and one neurofibrosarcoma. In 24 of 66 dogs examined, metastases of extracardiac neoplasms were found in the heart (15 carcinomas, six malignant lymphomas, three haemangiosarcomas). In cats, one case of primary haemangiosarcoma of the pericardium and five cases of secondary cardiac tumours (two malignant lymphomas, three carcinomas) occurred. Cardiac neoplasms in cats were not identified clinically but were detected by detailed gross sectioning of the heart (n=2) or histopathological examinations (n=3). This study showed an unexpectedly high number (36%) of dogs with cardiac metastases.