Bilateral retiform Sertoli-Leydig cell tumour in a bitch. Alpha-inhibin and epithelial membrane antigen as useful tools for differential diagnosis.

Sertoli-Leydig cell tumours with a retiform pattern similar to the pattern of the rete testis are a subtype of sex cord-stromal tumours recognized in the human WHO histological classification of ovarian tumours but not in the equivalent classification for domestic animals. The morphology of the tumour may be confused with that of the more common ovarian epithelial tumours. The gross, microscopical and immunohistochemical features of a canine retiform Sertoli-Leydig cell tumour and its comparison with the human counterpart are presented in this report. Both ovaries were enlarged and cystic. Microscopically, the tumour was cystic with tubulopapillary growth characterized by narrow, elongated branching tubules. Immunohistochemically, the tumour cells expressed alpha-inhibin, while epithelial membrane antigen was not detected, indicating a sex cord-stromal origin of the tumour. Additionally, the tumour cells expressed cytokeratin and vimentin in addition to oestrogen receptor alpha and progesterone receptor.