Mucinous Cystadenoma of the Ovary Associated with Hyperplasia of Stromal Leydig Cells in Pregnant Woman

Background: The hormonally induced non-neoplastic lesions of ovarian stroma during pregnancy must be recognized by pathologist in order to avoid mistaking them for true tumors. Case report: A 28-year-old woman was delivered of a healthy infant by cesarean section. As an incidental finding, a multicystic tumor in the left ovary was found and resected. Histopathology was consistent with benign mucinous cystadenoma. In addition, within the stroma beneath the lining mucinous epithelium, a dense population of cohesive polygonal cells with abundant eosinophilic cytoplasm, typically resembling the Leydig cells, was seen. They were uniform without atypia, accompaning by minimal proliferative activity. They strongly expressed vimentin, inhibin, CD99 and calretinin. The final diagnosis of mucinous cystadenoma associated with hyperplasia of stromal Leydig cells was made. Conclusions: Leydig cell hyperplasia belongs to the specific changes of ovarian stroma associated with pregnancy. The present case stresses that in such situation the pathologists should be aware of it and not confuse it with a tumor.