Posted by Article on 2/25/2002, 8:49 am

American Journal of Roentgenology AJR 2000; 175:353-358 © American Roentgen Ray Society Pictorial Essay Pelvic Endometriosis Various Manifestations and MR Imaging Findings Christina A. Gougoutas1, Evan S. Siegelman1, Jennifer Hunt2 and Eric K. Outwater3 1 Department of Radiology, University of Pennsylvania Medical Center, 3400 Spruce St., 1st Floor Silverstein, Philadelphia, PA 19104-4283. 2 Department of Pathology, University of Pennsylvania Medical Center, 6th Floor Founders, Philadelphia, PA 19104-4283. 3 Department of Radiology, University of Arizona Medical Center, 1501 N. Campbell Ave., Rm. 1361, Tucson, AZ 85724-5067. Received November 15, 1999; accepted after revision January 24, 2000. Address correspondence to E. S. Siegelman. Introduction Endometriosis is defined as the presence of endometrial glands in locations outside the uterus. The ectopic endometrium responds to hormonal stimulation with various degrees of cyclic hemorrhage that result in suggestive symptoms and appearances. Recent awareness of the increasing incidence of endometriosis in asymptomatic women has led to the hypothesis that endometrial implants are in fact physiologic and do not in themselves indicate a disease process until recurrent bleeding occurs in these implants, causing symptoms and progressive disease [1]. The three hallmarks of endometriosis are peritoneal endometrial implants, endometriomas (endometriotic cysts), and adhesions. The most common peritoneal sites of involvement (in decreasing order of frequency) are the ovaries, uterine ligaments, cul-de-sac, and pelvic peritoneum reflected over the uterus, fallopian tubes, rectosigmoid, and bladder. Rare extraperitoneal sites include the lungs and the central nervous system. Because sonography is usually the first technique performed for evaluation of pelvic disease during the reproductive years, it can aid diagnosis and treatment of endometriosis. Sonography may not differentiate some endometriomas from hemorrhagic cysts or other ovarian neoplasms and is insensitive in the detection of peritoneal implants. Because of these limitations, laparoscopy has remained the standard of reference for diagnosis and staging of pelvic endometriosis. Laparoscopy does not visualize well "atypical" nonpigmented extraperitoneal sites of involvement and, particularly, regions obscured by pelvic adhesions. MR imaging may be an alternative for evaluation of endometriosis before surgery. MR imaging has shown a sensitivity and specificity of greater than 90% in the detection of endometriomas, with its main limitation being the detection of small (<3 mm) peritoneal implants. The addition of fat-saturated T1-weighted imaging has improved diagnostic accuracy in the evaluation of both endometriomas and peritoneal disease by narrowing the dynamic range, increasing lesion conspicuity [2], and differentiating lipid-containing ovarian masses from those containing blood [3] (Fig. 1A,1B,1C). This pictorial essay shows the imaging spectrum of endometriosis with emphasis on unusual pelvic manifestations. Endometrial Implants The peritoneal implant represents the presence of endometrial surface epithelium and stroma embedded in serosal tissues in the peritoneal cavity. The ectopic location of endometrium in the peritoneal cavity causes reactive proliferation of the stromal vessels that leads to recurrent hemorrhage. The implant has a varied appearance depending on the age of associated blood products. Pathologically, the implants begin as red highly vascular lesions, typically 2-3 mm. Recurrent bleeding and inflammation cause fibrosis and hemosiderin deposition, leading to a raised nodular "powder burn" lesion. Lack of detection of these small foci of peritoneal involvement has been a major limiting factor in the acceptance of MR imaging as a staging tool for pelvic endometriosis. Endometriomas Endometriomas ("chocolate cysts") of the ovary contain dark gelatinous material surrounded by a fibrous wall of variable thickness. Endometriomas are usually multiple and bilateral. They are characteristically homogeneously hyperintense on T1-weighted sequences with relatively low signal intensity on T2-weighted sequences (Fig. 2A,2B,2C,2D). This loss of signal intensity on the T2-weighted sequences is caused by high concentrations of intracystic methemoglobin and other protein or iron products [4]. Some lesions are heterogeneous in signal intensity because the blood products are in various stages of degradation from multiple episodes of bleeding. As free water in the cyst is resorbed, the concentration of iron increases along with the viscosity of the cyst contents. Takahashi et al. [5] have shown the density (chronicity) of cyst contents to be directly proportional to the iron concentration, with a corresponding decrease in the T2 relaxation time as the concentration of iron and the viscosity of cyst fluid increase. Iizuka et al. [6] have also shown that the concentration of iron in an ovarian cyst helps in differentiating endometriomas from serous cystadenocarcinomas, which do not contain a high concentration of iron. Endometriotic cysts may contain a peripheral rim of low signal intensity representing hemosiderin or fibrous capsule (Fig. 2A,2B,2C,2D). Enhancement of the periovarian peritoneal surfaces after contrast material administration may occur [7] (Fig. 2A,2B,2C,2D). Large endometriomas may contain multiple thin septations and frequently show hematocrit levels. Endometriomas may predispose the ovary to twist less often than other ovarian masses, possibly because of surrounding adhesions. The diagnosis of ovarian torsion may be established with MR imaging by showing an endometrioma in an enlarged poorly enhancing ovary with peripherally located follicles (Fig. 3A,3B,3C).

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