A Rare Case of Thecoma In a Dog

Thecoma is an ovarian tumour which has rarely been described in dog and must be differentiated from other similar neoplasm such as granulosa cell tumour, clear cell carcinoma, luteoma, fibroma, above all by histopathological examination. Aim of the paper is to report the histochemical and immunohistochemical findings useful to identify this tumour rarely found in dog. Tumour tissue was negative for cytokeratin and HBME-1, whereas strong immunopositivity with vimentin, calretinin and inhibin was seen; Gomori histochemical stain highlighted an abundant reticulin network among neoplastic cells. Negativity to cytokeratin and HBME-1 excluded the differential diagnosis of fibroma, while positivity to vimentin, calretinin and inhibin supported the differential diagnosis of granulosa cell tumour. The absence of spindle cells and strong presence of reticulin among tumour cells confirmed the final diagnosis of thecoma.