They are the most common solid benign tumors of the ovary. Fibromas and fibrothecomas may mimic pedunculated myomas on US, appearing as well-circumscribed, hypoechoic, and solid round or oval tumors with sound attenuation. On color Doppler, they are usually hypovascular. Fibromas are sometimes associated with ascites and pleural effusion (Meigs syndrome). On MRI, due to the extensive collagen content and hyalinized tissue, fibromas and fibrotic component of fibrothecomas appear as intermediate SI masses on T1- and low SI masses on T2- WI. There may be scattered foci of high SI on T2-WI due to cystic degeneration or edema. Calcification may occur, seen as foci of signal voids on T1- and T2-WI. After administration of gadolinium, there is typically delayed lowlevel enhancement. Thecomas contain a prominent lipid component that can be demonstrated on chemical-shift imaging or on frequency-selective FS-MRI. Due to estrogen secretion, endometrial hyperplasia may be present.

Brenner tumors are transitional cell tumors of the ovary. The majority is benign, but borderline and malignant types can also arise. Benign tumors are usually unilateral, small (<5 cm), and hypoechoic on US. Extensive calcification is characteristic, resulting in posterior acoustic shadowing on US. On MRI, the benign type appears solid and of low SI on both T1- and T2-WI. They demonstrate lower SI on T2-WI than other solid tumors. Ipsilateral ovarian tumors (e.g., mucinous cystadenomas) may be present in 30% of cases, and endometrial hyperplasia can also occur.

Tumors such as these include surface epithelial tumors (serous cystadenocarcinomas, mucinous cystadenocarcinomas, endometrioid, and clear-cell carcinomas), sex cord-stromal tumors (granulosa cell and Sertoli-Leydig cell tumors), and germ cell tumors. Less common malignant tumors are mixed Müllerian tumors, undifferentiated carcinomas, carcinoids, and lymphomas.

Borderline serous tumors account for 10–15% of all ovarian serous tumors and are bilateral in 30% of cases. Likelihood of malignancy increases with the presence of septations, mural nodules, and papillary projections (Fig. 4). MRI features suspicious for malignancy include: mass >4 cm, cystic lesion with solid component, irregular wall thickness >3 mm, septal thickness >3 mm, presence of papillary projections or nodules, and presence of solid mass with necrosis and early, bright contrast enhancement [23, 24]. In addition, ancillary criteria for suspected malignancy include: direct local invasion, peritoneal deposits, enlarged lymph nodes, and ascites. DW-MRI is highly sensitive and specific in detecting the extent of peritoneal disease. CE-CT remains the technique of choice for staging ovarian carcinoma (Fig. 5).