Clinical and pathological features of a cardiac chondrosarcoma in a dog

PRIMARY cardiac tumours are rare in human and veterinary medicine and tumour-specific diagnosis has been made most often at postmortem examination. In veterinary medicine, cardiac tumours are sporadic, with a prevalence of 0·17 to 0·19 per cent in dogs (Ware 1995, Ware and Hopper 1999). The most commonly reported tumours in dogs are haemangiosarcomas and chemodectomas, although other types of cardiac neoplasm have been reported (Bright and others 1990, Ware and Hopper 1999). Cardiac chondrosarcomas are extremely rare in veterinary medicine. Although different subtypes of chondrosarcoma are reported in human medicine (Casadei and others 1991), there are few reports of this tumour in dogs (Greenlee and Liu 1984, Albers and others 1997, LaRock and others 1997). This short communication describes the clinical and pathological features of a cardiac chondrosarcoma in a dog. A 12-year-old intact female poodle weighing 8 kg was presented to the Veterinary Teaching Hospital of the Complutense University of Madrid with a history of gradual dyspnoea and exercise intolerance. On physical examination the dog was dull, with a moderately distended abdomen, severe tachypnoea, expiratory dyspnoea and abdominal breathing. The mucous membranes were pale, its rectal temperature was normal, heart sounds were muffled but the rhythm was regular, the femoral pulses were weak and jugular distension was evident. A red blood cell count was within the normal reference range, whereas a white blood cell (WBC) count was moderately increased (20·3 x 109 WBC/litre, reference range 6 x 109 to 16 x 109 WBC/litre), with neutrophilic predominance. The plasma protein, glucose, urea, creatinine, gamma glutamyl transferase, alkaline phosphatase, cholesterol, calcium, potassium and sodium levels were all within the reference ranges. Left lateral and dorsoventral thoracic radiographs showed a moderate amount of pleural fluid and the cranioventral border of the heart was obscured. An electrocardiogram showed a normal sinus rhythm, 120 bpm with no anomalies. Twodimensional Doppler and colour Doppler echocardiography were performed using an ultrasound machine (AU3 ultrasound machine; Esaote) and a 10 MHz transducer. Twodimensional echocardiography showed dilatation of the right atrium and ventricle, a paradoxical septal motion of the ventricular septum and a hyperechoic tissue in the right inflow tract (Fig 1). The mass was homogeneous and appeared to be attached to the tricuspid valve septal leaflet and moved with the valve, without causing occlusion of right atrium or ventricle. Continuous-wave Doppler revealed an obstructive flow pattern through the right ventricular inflow. A presumptive diagnosis of a cardiac tumour was made and, because of the poor prognosis, the owners decided to have the dog euthanased. At postmortem examination, a 3 x 4 x 4 cm pedunculated white mass was found in the lumen of the right ventricle. It was attached to the ventricular septum and appeared to arise from the mural endocardium near the tricuspid valve. The cut surface of the mass was shiny and white, with multifocal friable and firm regions, and some irregular cavities (Fig 2). The liver had a moderately accentuated lobular pattern, but the other viscera had no macroscopic changes. Grossly, visible metastases were not detected. Tissue samples from all major organs were fixed in 10 per cent buffered formalin for routine histological processing. Haematoxylin and eosin stain, and Ki-67 immunohistochemical procedures were performed. The anti-Ki-67 monoclonal MIB-1 antibody is a nuclear proliferation marker useful for studying cell proliferation in neoplastic lesions. The monoclonal MIB-1 antibody reacts with the Ki-67 nuclear antigen associated with cell proliferation. This reaction is found throughout the cell cycle (G1, S, G2, M phases) and is absent in resting (G0) cells. Histologically, the mass was composed of intersecting bundles of fusiform cells in a variably collagenous stroma closely associated with numerous lobules of cartilaginous tissue, but no myxomatous component was observed. The fusiform tumour cells had marked anisokaryosis. The neoplastic tissue appeared to arise from the mesenchymatous subendocardial tissue (Fig 3). This observation was similar to a soft tissue chondrosarcoma of mesenchymal subtype (Casadei and others 1991) and to a primary mesenchymal chondrosarcoma in the pericardium of a dog (LaRock and others 1997). The histology of the mass was similar to cardiac chondrosarcomas (Greenlee and Liu 1984, Southerland and others 1993, Albers and others 1997, LaRock and others Veterinary Record (2004) 155, 678-680