Magnetic resonance manifestations of decidualized endometriomas during pregnancy

Decidual changes of endometrial tissue in endometriomas during pregnancy may manifest as mural nodules and mimic malignant transformation. We evaluated magnetic resonance findings of decidualized ovarian endometriomas for the differentiation from malignant transformation. Magnetic resonance manifestations of 5 decidualized ovarian endometriomas were evaluated. High b-value diffusion-weighted images were performed in 3 cases. The mural nodules were demonstrated as linear, small nodular, broad-based nodular, or polypoid structures, which showed prominent hyperintensity on T2-weighted images and on diffusion-weighted images similar to normal endometrium or placenta. The apparent diffusion coefficient of decidualized mural nodules was significantly higher than that of malignant mural nodules of 7 ovarian cancers. Endometrioma with prominent hyperintense mural nodules on T2-weighted images in a pregnant woman is highly suggestive for decidualized endometriomas. Diffusion-weighted images with the apparent diffusion coefficient measurement may help the diagnosis of this rare entity.