Fluid-fluid levels in ovarian teratomas

Background: We evaluated the imaging features of ovarian teratomas containing fluid-fluid levels on ultrasonography (US). Methods: We retrospectively reviewed US examinations of two groups with 805 masses (370 benign ovarian teratomas and 435 nonteratomatous adnexal masses). Results: In 27 teratomas and eight nonteratomatous adnexal masses, fluid-fluid levels were detected on US. According to the echogenicity of each layer, 27 teratomas were classified as three types: 1, supernatant hypoechoic and dependent hyperechoic layers (n = 16) 2, supernatant hyperechoic and dependent hypoechoic layers (n = 8); and 3, supernatant hypoechoic and dependent hypoechoic layers with bright fluid interface (n = 3). In eight (30%) of 27 teratomas, US showed floating nodules at the interface, five of which had posterior acoustic shadowing. All eight nonteratomatous adnexal masses showed type 1 fluid-fluid levels. Conclusion: The fluid-fluid level seen on US is strongly suggestive but not pathognomonic of dermoids. Fluid-fluid levels with supernatant hyperechoic and dependent hypoechoic layers, supernatant hypoechoic and dependent hypoechoic layers with bright interface, and a floating nodule might pathognomonic findings of benign ovarian teratomas.