Pelvic endometriosis: MR imaging spectrum with laparoscopic correlation and diagnostic pitfalls

Endometriosis is a common multifocal disease involving a number of anatomic sites in the pelvis. Although laparoscopy is the standard of reference for diagnosis, magnetic resonance (MR) imaging is a noninvasive method for evaluating areas inaccessible to laparoscopy. A large endometrioma (> or = 1 cm in diameter) appears as a homogeneously hyperintense mass on T1-weighted MR images and as a low-signal-intensity mass with areas of high signal intensity on T2-weighted images. A small endometrioma may be indicated when a pelvic mass less than 1 cm in diameter is hyperintense on T1-weighted images irrespective of its appearance on T2-weighted images. Endometriosis may also manifest as multiple, homogeneously hyperintense cysts on T1-weighted images. Involvement of the alimentary tract or bladder can appear as areas of high signal intensity. Although MR imaging is limited in its ability to depict small endometrial implants and adhesions, the advantages of MR imaging over laparoscopy include the ability to characterize endometriotic lesions and to evaluate extraperitoneal sites of involvement, contents of a pelvic mass, or lesions hidden by dense adhesions. The roles of the two modalities are therefore complementary. Knowledge of the variety of MR imaging appearances of endometriosis and organ involvement within the pelvis is important for guiding a subsequent laparoscopic examination.