Extraskeletal osteosarcoma of the thorax in a goat: case report
© Braun et al; licensee BioMed Central Ltd. 2011
Received: 18 October 2010
Accepted: 19 September 2011
Published: 19 September 2011
This report describes the results of clinical, ultrasonographic and computed tomographic examination of a 16-year-old goat with extraskeletal osteosarcoma of the thorax.
The lead clinical signs were abnormal condition and demeanour, fever, tachycardia, tachypnoea, dyspnoea and dilated jugular veins. Ultrasonographic examination of the thorax revealed a precardial mass, measuring 16.4 by 11.4 by 14.2 cm. Computed tomographic examination showed dorsocaudal displacement of the trachea, heart and lungs to the right. A tentative diagnosis of mediastinal or pleural neoplasia was made, and the goat was euthanased and necropsied. A definitive diagnosis was based on histological examination of the mass.
To our knowledge, this case report is the first description of extraskeletal osteosarcoma of the thorax in goats and serves to broaden the diagnostic spectrum of thoracic diseases in this species. Extraskeletal osteosarcoma should be part of the differential diagnosis in goats with thoracic tumours.
Tumours of the thorax are rare in goats . Thymoma is the most common thoracic neoplasia in this species [2–6] and there are a few reports of lymphosarcoma and ovine pulmonary adenocarcinoma . To the authors' knowledge, osteosarcoma has not been described in goats. Osteosarcoma occurs most commonly in the long bones and is rare in domestic animals other than cats and dogs . Osteosarcoma may occur in organs other than the skeletal system, and the absence of a primary bone lesion is a prerequisite for the diagnosis of extraskeletal osteosarcoma. In dogs, extraskeletal osteosarcoma has been reported in the spleen, gastrointestinal tract, urogenital tract, liver, skin, mammary gland and subcutis [8–10]. A dog with osteosarcoma of the os penis was recently described . Osteosarcoma commonly metastasizes in dogs, and haematogenous metastasis is more common than lymphogenous metastasis . The major target organs include the lungs, liver, mediastinum, omentum and heart . There have been two reports on osteosarcoma in goats; one case involved osteosarcoma of the humerus in a Toggenburg goat  and the other described osteosarcoma of the metacarpus of a seven-year-old Alpine goat . The purpose of this report was to describe the clinical, ultrasonographic and computed tomographic findings in a goat with extraskeletal osteosarcoma.
A 16-year-old castrated male miniature goat was referred to our clinic because of poor appetite, tachypnoea and tachycardia of several weeks duration. The general condition and demeanour were abnormal, the rectal temperature was 40.2°C (normal, 38.1- 40.0°C, ), the heart rate was 160 beats per minute (normal, 70 - 90 beats per minute, ) and there was a mild arrhythmia. Both jugular veins were distended. The goat had dyspnoea, abdominal respiratory effort and a respiratory rate of 60 breaths per minute (normal, 15 - 30 breaths per minute, ). Auscultation of the lungs revealed increased respiratory sounds. Examination of the intestinal and urinary tracts, musculoskeletal system and central nervous system yielded no abnormal findings.
Based on reference values established in this clinic , the activities of glutamate dehydrogenase (103 U/l, normal 3.1 - 19.8 U/l) and sorbitol dehydrogenase (128 U/l, normal 20.4 - 68.7 U/l) were increased and the serum concentrations of magnesium (0.64 mmol/l, normal 0.9 - 1.4 mmol/l) and inorganic phosphate (0.85 mmol/l, normal 1.2 - 2.9 mmol/l) were decreased. Other biochemical variables and a complete blood cell count were within normal limits.
The lead clinical signs in this patient were bilateral distension of the jugular veins, tachycardia and tachypnoea. Distension of the jugular veins primarily suggests right-sided cardiac insufficiency, but in the absence of cardiac signs, may indicate obstruction of the cranial vena cava by a thrombus or compression of the vein by an abscess, tumour or thoracic effusion . In our patient, right-sided cardiac insufficiency could not be ruled out because of the tachycardia and arrhythmia and the right ventricle appeared enlarged on ultrasonograms. However, a combination of ultrasonography, radiography and CT allowed a tentative diagnosis of a tumour. The CT exam provided detailed images of the thoracic organs, which could not be accomplished with ultrasonography. A recent CT study of the thorax in 26 healthy goats  was very helpful for interpreting the lesions in our patient. An abscess was not part of the differential diagnosis because the total leukocyte count and concentrations of fibrinogen and total solids were within the reference ranges. The advanced age of our patient favoured a diagnosis of neoplasia. Differential diagnoses for the thoracic tumour included thymoma, thymic lymphoma , metastatic carcinoma and tumour of the aortic bodies. Thymic lymphoma tends to occur in younger animals, whereas thymoma has been reported more often in adult or aged animals . Furthermore, regional lymph nodes, which were normal in our patient, are commonly involved in thymic lymphoma, but not in thymoma. A fine needle aspirate or ultrasound-guided biopsy of the mass was not carried out because of the grave prognosis and advanced age of the patient. Instead, a postmortem examination served to provide a definitive diagnosis. Because there were no indications of skeletal involvement, the osteosarcoma was considered extraskeletal. Extraskeletal osteosarcoma has been described in dogs, primarily in the mammary gland, spleen, gastrointestinal and urogenital tracts, liver, skin and subcutis . However, to our knowledge, this tumour has not been reported in domestic animals. Interestingly, a pleural osteosarcoma with pulmonary involvement was recently described in the human literature .
The differential diagnosis in goats with distended jugular veins, tachycardia and tachypnoea should include abscess and neoplasia in addition to right-sided heart failure. Ultrasonography, radiography and computed tomography are useful for diagnosing neoplasia and determining the extent of the lesions. To our knowledge, this case report is the first description of extraskeletal osteosarcoma of the thorax in goats and serves to broaden the diagnostic spectrum of thoracic disease in this species. Extraskeletal osteosarcoma should be part of the differential diagnosis in goats with thoracic neoplasia.
Consent was obtained from the owner of the goat for publication of this case report and any accompanying images.
The authors thank Dr Rolf Kamber for referring the goat to our clinic, the technicians of the Medical Laboratory for the haematological and biochemical analyses and the animal assistants for looking after the goat.
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