leydig cell tumor in ovary of a german shepherd bitch: an immunohistopathological study

leydig cell tumor as a sex-cord stromal tumor is a relatively uncommon ovarian tumorin bitch. a 10-year-old female german shepherd dog was presented because of protrusion of a large tumor-like mass of 16 × 14 × 7 cm in dimensions from her vagina. after stabilization of the patient, the mass was removed surgically and concurrent ovariohysterectomy was also performed. macroscopically, the healthy tissue of the right ovary was totally replaced by a homogeneous, brown and firm mass. the neoplasm was well-circumscribed and nodular and it was clearly demarcated from the healthy tissue. histological examination revealed the presence of solid sheets and acinar structures composed of polyhedral to elongated cells. the neoplastic cells had large, eosinophilic, and vacuolated cytoplasms with round to oval nuclei and expressed vimentin on immunohistochemical examination. these gross, microscopic and immuno-histochemical features are characteristics of ovarian leydig cell tumor.