A rare case of haemangiopericytoma in an Amazon Parrot

A 20-year-old male Amazon parrot (Amazona ochrocephala) was presented with a history of a painless mass developing over six months. On clinical examination a firm, well defined, 2.52cm mass was palpated at the right pelvic area. Haematology and biochemistry were normal while radiography revealed that there was no bone involvement. The tumour was removed under general anaesthesia. The bird recovered fully and remains tumourfree two years post-surgery. The tumour was ovoid, whitish and moderately hard in cut section. Histologically, the mass was well demarcated and composed of spindle or fusiform cells sparsely arranged in perivascular whorls or in loose interlacing bundles, giving the lesion a translucent appearance. Tumour cells were mildly pleomorphic with few mitoses. Based on the above, a diagnosis of benign haemangiopericytoma was offered, the first reported in this species. However, haemangiopericytoma, which is usually reported in dogs, is mainly composed of polygonal or spindle cells with uniform, ovoid, plump nuclei in that species. Furthermore, the presence of small wavy spindle cells partly arranged in interlacing bundles, albeit not a dominant feature, was reminiscent of a benign peripheral nerve sheath tumour (BPNST/ schwannoma) and allowed this diagnosis to be entertained. For this reason, immunohistochemistry was performed employing a streptavidin-biotin-peroxidase protocol. Tumour cells were positive for S-100 and aSMA but not GFAP. Most cells arranged perivascularly or in bundles were positive for PCNA and vimentin, suggesting that they belong to the same tumour cell population. The immunohistochemical profile was consistent with and further established the diagnosis of haemangiopericytoma. This report demonstrates the value of immunohistochemistry, through the application of a specific panel of antibodies, in differentiating between haemangiopericytoma and BPNST.