Brenner tumors.

Brenner tumors are rare ovarian neoplasms composed of ovarian transition cells surrounded by dense fibrous tissue. Most of them are small tumors (<2 cm), detected incidentally in asymptomatic women. Its predominantly fibrous content results in relatively low signal on weighted images, establishing differential diagnosis with ovarian fibroma and thecoma. Their imaging features are very similar, the differentiation is based on secondary characteristics, such as signs or symptoms of estrogen excess and the presence of a second ovarian neoplasm, which has been reported in up to 30% of patients with Brenner tumor. Although originally thought to be universally benign, there have been scattered reports in the past decades of borderline and malignant forms of Brenner tumors.