HISTORY

A six-year-old Golden Retriever was presented suffering from lameness in all four limbs. Radiographs revealed the presence of hypertrophic osteopathy. Thoracic radiographs showed the presence of a mass, cranial to the heart. Heartworms were seen in the blood smear and the Elisa test was positive; a Borrelia sp. test was also positive. Adult worms could not be detected with cardiac ultrasounds, however an enlargement of the right chambers were seen. Thoracic ultrasound revealed a cranial hyperechoic mass, fine-needle aspiration clearly showed the presence of fibroblasts, neutrophils and microfilariae. The mass was histologically compatible with a mesenchymal fibroma, soft tissue hyperplasia, or a very well differentiated fibrosarcoma. We repeated the aspiration twice and obtain similar results.

The animal was treated for heartworm infestation. Corticosteroids and analgesics were also administered. The animal condition got worse after a slight improvement. New radiographs showed an enlargement of the thoracic mass and euthanasia was recommended.

At necropsy, a mass extending to the right cranial and middle lung lobes were confirmed. Pathology study confirmed the presence of a fibrosarcoma, no worm infection or microfilariae were seen, although microfilaria could be detected in imprints done from the tumor before the histopathology study.

DISCUSSION

Hypertrophic osteopathy and its association with pulmonary masses have been long well described. In this case, the post-mortem diagnosis confirms the presence of pulmonary fibrosarcoma. It is, undoubtedly, the cause of the osteopathy. At first, we thought about a possible pulmonary granulomatosis secondary to dirofilariasis but, in view of the diagnosis of fibrosarcoma and the fact that we discovered the presence of microfilariae within it, a possible relation between dirofilariasis and fibrosarcoma (just as the documented relation between Spirocerca lupi infection and pulmonary fibrosarcoma) could be possible. Interstitial pulmonary fibrosis and important pulmonary parenchymal alterations associated to dirofilariasis (in vessels and bronchioles not reached by the parasite) have been previously described. These changes are possibly caused by growth factors derived from platelets and by other trophic factors stemming from the arteries damaged by the parasite. All this, plus the fact that the Golden Retriever is a predisposed breed to fibrosarcomas, can justify a possible relation between fibrosarcoma and dirofilariasis, the late being an etiologic agent of the first.