Extraskeletal osteosarcoma in the pericardium of a dog.

Abstract

OSTEOSARCOMA is a common malignant tumour in dogs (Thompson and Pool 2002), but extraskeletal osteosarcoma rarely arises in soft tissues (Patnaik 1990, Langenbach and others 1998). Previous reports have described extraskeletal osteosarcomas in various organs in dogs (Brodey and others 1969, Norrdin and Lebel 1971, Eckerlin and others 1976, Alexander and others 1979, Seiler 1979, Jaraj and others 1981, Smolowitz and Carpenter 1988, Fox and others 1994, Ringenberg and others 2000), including primary intracardiac osteosarcoma (Shelling and Moses 1994). However, no osteosarcomas arising in the pericardium have been reported. This short communication describes a case of extraskeletal osteosarcoma in the pericardium of a dog. An 11-year-old beagle weighing 13·6 kg was referred to the Nihon University Animal Medical Center with depression, anorexia and coughing. Physical examination revealed loss in weight, a decrease of femoral arterial pressure and tachycardia (204 bpm). However, the refilling times of the mucous membranes and capillaries were normal and there was no cardiac murmur. A complete blood count revealed leucocytosis (29,100 cells/μl, reference range 6000 to 12,000 cells/μl), and serum biochemistry demonstrated an increased activity of serum alkaline phosphatase (1145 U/litre; reference range 23 to 212 U/litre) and increased C-reactive protein (16 mg/dl; reference range <1·0 mg/dl). Diminished QRS voltages (0·94 mV lead II) were observed on electrocardiography. On right lateral radiographs of the thorax, severe cardiac enlargement and poorly defined mineralisation were identified in the cardiac shadow. On right parasternal short-axis echocardiography views, a large soft tissue mass of approximately 83 x 38·5 mm was present in the area cranial to the right ventricle. The mass adhered to the parietal pericardium but was separated from the epicardium. The pericardium was diffusely thickened to approximately 5 mm. The mass did not move with each heart beat. Although it was difficult to quantify the pericardial fluid by echocardiographic examination, a small amount of effusion was suspected. On a transverse section image of a computed tomographic (CT) scan performed under general anaesthesia, mineralisation was also identified in the pericardial cavity, and samples were collected by needle biopsy. These findings indicated the presence of a partially mineralised tumour which had arisen from the pericardium and formed in the pericardial cavity (Fig 1). No further treatment was carried out at the owner’s request, and the dog was returned to its owner. Histopathological examination of the biopsy samples showed a proliferation of ovoid and short fusiform cells with chromatin-rich, dark nuclei (Fig 2a). There were also plump