MR features of fluid-fluid levels in ovarian masses

To evaluate retrospectively the frequency and imaging features of fluid-fluid levels (FFLs) in pathologically proven ovarian masses on magnetic resonance (MR) images. The authors reviewed the preoperative MR findings of 556 ovarian masses in 428 patients. Presence, numbers, and signal intensities (SI) of FFLs were analyzed. In non-teratomas, we assessed whether SI of the FFLs of benign masses and malignant neoplasms differed using the chi(2) test. FFLs were observed in 66 of 556 ovarian masses (11.9%) on MR images, fat-fluid levels were observed in 11 of 80 teratomas, and FFLs attributed to hemorrhage in 54 of 476 non-teratomas and one twisted teratoma. Non-neoplastic cystic lesions were most common non-teratomas to contain FFLs (27/197, 13.7%), followed by malignant neoplasms (23/177, 13.0%). Benign neoplasms rarely contained FFLs (4/102, 3.9%); those that did were commonly associated with complications such as torsion or inflammation. A hypointense supernatant layer together with a hyperintense dependent layer on T1-weighted images (T1WIs) was significantly more common in malignant neoplasms than in benign masses (P < 0.0001). FFLs occurred in various ovarian masses ranging from benign to malignant neoplasms on MR images. In non-teratomas, a hypointense supernatant layer and a hyperintense dependent layer on T1WIs may favor a diagnosis of malignancy.