Benign epithelial ovarian tumors arise from the external surface of the ovary, a single layer of cells derived from the coelomic epithelium. There are several major classifications of benign epithelial ovarian tumors based on histologic origin: serous, mucinous, Brenner, endometrioid, clear cell, and mixed.

Serous tumors are composed of cells resembling the fallopian tube lining. Benign serous tumors represent about two-thirds of benign ovarian epithelial tumors. These tumors commonly affect women in their 30s and 40s. Approximately 10%-20% of these tumors are bilateral. The most common are serous cystadenomas, which typically are smooth, thin-walled cysts filled with clear or straw-colored fluid.

Mucinous tumors are composed of cells resembling the intestinal epithelium or the endocervical epithelium. These tumors represent about 10%-15% of benign ovarian tumors and commonly affect women in their 30s and 40s. Most benign mucinous tumors are unilateral. The most common are mucinous cystadenomas, which typically are smooth, multiloculated cysts filled with viscous fluid.

Brenner tumors are composed of cells resembling the transitional epithelium of the bladder. These tumors represent about 3% of benign ovarian epithelial tumors. Brenner tumors typically affect women in their 40s and 50s. These tumors are typically unilateral. Typically, these tumors have a tan to yellow external surface and can be firm to palpation.

Endometrioid tumors are composed of cells resembling the uterine proliferative endometrial lining. These tumors represent less than 1% of benign ovarian tumors and commonly affect women in their 50s. The most common subtype is endometrioid adenofibromas. These tumors primarily have a smooth outer surface with a firm internal component containing several cystic spaces. The cystic spaces can have variable contents including clear fluid, mucinous material, or hemorrhagic debris. These tumors can be associated with endometriosis.

Benign clear cell tumors are extremely rare, and only a few reported cases exist in the literature.

Related topics: borderline epithelial ovarian tumor, ovarian cyst