Which type of benign ovarian tumor is typically bilateral?

Serous cystadenomas are benign ovarian tumors that are often bilateral, meaning they can affect both ovaries simultaneously. These tumors are characterized by their cystic structure and typically arise from the surface epithelium of the ovary. Serous cystadenomas are filled with clear serous fluid and can vary in size.

The bilateral nature of serous cystadenomas is an important distinguishing feature, especially when considering the differential diagnosis of ovarian masses. While other ovarian tumors can also be found bilaterally, serous cystadenomas have a higher tendency to manifest on both sides.

In contrast, fibromas, dermoid cysts, and endometriomas typically are unilateral, occurring on one side of the ovary. Fibromas are solid tumors made of connective tissue, dermoid cysts are teratomas that can contain varied types of tissue (like hair and teeth), and endometriomas are associated with endometriosis, presenting as cystic structures filled with altered blood.

Thus, the specific characteristics and common clinical presentation of serous cystadenomas make them the most likely benign ovarian tumor encountered bilaterally.