Despite the common occurrence of endometriosis in women, the medical literature offers very little to illuminate the rare instances in which the often painful yet benign cysts become ovarian tumors. Japanese researchers say they have published the first English-language information on MR findings characterizing such cancers in the latest edition of the American Journal of Roentgenology.
Researchers from the Shimane Medical and Tsukuba universities, looking at what they acknowledge is a very small sample of patients, found that endometrial cysts with malignant transformation "rarely show low signal intensity on T2-weighted MR images." However, "They usually have enhancing nodules that are most clearly depicted on dynamic subtraction imaging," the researchers wrote (AJR, November 2000, Vol. 175:5, pp. 1423-1430).
According to the literature, the mural nodules on the wall of endometrial cysts are considered to be diagnostic of malignant transformation. The nodules can also be enhanced with meglumine gadopentetate.
"However, it is difficult to evaluate the contrast enhancement of mural nodules because endometrial cysts have high signal intensity on T1-weighted images caused by the presence of deoxyhemoglobin or methemoglobin from old hemorrhage, and the mural nodules are often very small," the authors noted.
Therefore, the goal of the study was to describe the MR imaging features of the malignant transformation of endometriosis, and find the most useful method of evaluating the contrast enhancement of the mural nodules surrounded by hyperintense fluid on T1-weighted images.
In their study, the researchers imaged 10 patients with pathologically and surgically confirmed ovarian adenocarcinoma in endometriomas between 1992 and 1999. Four of the patients were asymptomatic. Ten women with endometriosis and mural nodule-like structures on ultrasound images served as a control group.
Three different superconducting magnets were used to examine subsets of the patient group: a Gyroscan 1.5-tesla scanner (Philips Medical Systems, Shelton, CT), a Signa 1.5-tesla unit (GE Medical Systems, Waukesha, WI), and a Magnex 100 1.0-tesla system (Shimadzu Medical Systems, Torrance, CA). Axial T1- or T2-weighted spin-echo or fast spin-echo images were obtained for all patients, as were T1-weighted axial images enhanced with meglumine gadopentetate (Magnevist, Berlex Imaging, Wayne, NJ).
Two radiologists examined and discussed the images, finding that "endometriomas with malignant transformation were larger than contralateral benign endometriomas." They then summarized the MR features of the observed malignant and benign endometriomas.
Among their findings, all 10 masses with malignant transformation showed hyperintensity on T1-weighted images and had thick walls (maximum thickness of greater than 3 mm), the authors wrote.
"Additionally, all 10 masses in the control group had low signal intensity on T2-weighted images," they wrote. "This intensity pattern is believed to be caused by a magnetic susceptibility effect generated by hemosiderin in old hemorrhage, densely concentrated fluid, or fibrosis."
The researchers also determined that the asymmetry of the endometriomas did not seem as important as signal intensity on T2-weighted images. Mural nodules composed of deciduosis tended to appear multifocal and rectangular compared to the malignant transformation.
Perhaps most important, the group found that dynamic subtraction images consistently offered easy evaluation of contrast enhancement in mural nodules, while T1-weighted images, fat-saturated T1-weighted images, and dynamic contrast images rarely did.
"We recommend performing dynamic subtraction imaging when this uncommon entity is suspected," they concluded, adding that "patients with indeterminate sonographic findings and in whom there is a suspicion of endometriosis may benefit from MR imaging."
Several presentations at the upcoming RSNA conference will expound on the benefits and pitfalls of using MRI to image endometriosis: A group from Montreal will discuss the accuracy of MRI in detecting endometrial pathology in postmenopausal women (311). Dr. Bohyun Kim and colleagues from Seoul, South Korea will present a study on how to differentiate endometrial lesions with MRI (314). Finally, researchers from Beth Israel Deaconess Medical Center in Boston will offer a study on the classification problems associated with MR evaluation of uterine abnormalities (317).
By Tracie L. ThompsonAuntMinnie.com contributing writer
November 20, 2000
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