Malignant transformation of pelvic endometriosis: MR imaging findings and pathologic correlation.

Malignant transformation is a rare complication of endometriosis. Endometriosis-associated ovarian cancers are seen more often in younger women than are ovarian cancers without endometriosis, and early detection is important to improve the prognosis and preserve fertility. However, normal decidual change of the ectopic endometrium in an endometrioma during pregnancy must be differentiated from malignant transformation. The finding that is most important for a diagnosis of malignant change is the presence of one or more contrast material-enhanced mural nodules within a cystic mass at magnetic resonance (MR) imaging. Dynamic subtraction MR imaging is useful in depicting small contrast-enhanced nodules within the hyperintense endometrioma on T1-weighted images. Intracystic coagulate may mimic a mural nodule; the absence of contrast enhancement is the diagnostic clue to its benignity. Enlargement of the endometrioma and the disappearance of shading within the mass on T2-weighted images are suggestive of malignant transformation.