What is the role of MRI in the workup of endometrioma/endometriosis?

Updated: Dec 14, 2018
  • Author: Shawn Daly, MD; Chief Editor: Eugene C Lin, MD  more...
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The appearance of endometriomas on MRIs is variable and depends on the concentration of iron and protein in the fluid, which are products of blood degradation. [15, 17, 18] Most endometriomas have the gross appearance of chocolate cysts, representing highly concentrated blood products. MRI demonstrates these endometriomas as cystic masses with very high signal intensity on T1-weighted images and very low signal intensity on T2-weighted images.

MRI is an accurate technique in distinguishing endometriomas from other masses. MRI is more accurate in distinguishing benign from malignant ovarian masses than ultrasonography. [19, 20, 21]  In one study, MRI showed a sensitivity of 90-92% and a specificity of 91-98% for the diagnosis of endometrioma in patients with adnexal masses. [17] MRI is not sensitive for superficial implants; therefore, the modality should not be relied on to rule out endometriosis. False-negative findings are usually seen in patients with only peritoneal implants. These are generally too small to resolve with MRI or any noninvasive imaging technique. False-positive results can occur because cystic neoplasms or functional cysts can mimic endometriomas. Most hemorrhagic cysts and neoplasms do not show the degree of T1 and T2 shortening shown by endometriomas, because the concentration of iron even in whole blood is much less than that in endometriomas. [10, 22, 23]

(See the images below.)

T1-weighted magnetic resonance image of an endomet T1-weighted magnetic resonance image of an endometrioma. Note the characteristic high signal intensity (similar to that of fat) of this right-sided adnexal endometrioma (arrow).
Fat-saturated T1-weighted magnetic resonance image Fat-saturated T1-weighted magnetic resonance image of an endometrioma. In this right adnexal endometrioma (same lesion as in the previous image), fat saturation has been applied. Note that the endometrioma's (arrow) signal intensity does not decrease. This signal characteristic differentiates endometriomas from fatty adnexal masses, such as dermoids.
T2-weighted magnetic resonance image of an adnexal T2-weighted magnetic resonance image of an adnexal endometrioma (arrow; same lesion as in the previous image). Note the characteristic low T2-weighted signal. This low T2 signal is a result of the high iron concentration in the endometrioma.

This low signal intensity on the T2-weighted images is termed shading and occasionally occurs in a gradient from higher to lower signal intensity. This pattern of signal intensities results from the high iron concentration in the endometrioma and is rarely seen in other masses of any type. [10, 22]

In a study to determine the sensitivity and specificity of the T2 dark spot sign in helping distinguish endometriomas from other hemorrhagic adnexal lesions, 16 of 45 endometriomas, zero of 25 hemorrhagic cysts, and 2 of 4 serous cystadenomas demonstrated dark spots. Sensitivity, specificity, positive predictive value, and negative predictive value of T2 dark spots for differentiating endometriomas from other hemorrhagic cystic ovarian masses were 36%, 93%, 89%, and 48%, respectively. The T2 shading sign was found to be sensitive but not specific for endometriomas. [24]

Multiple high signal lesions, usually in the ovaries, on T1-weighted images are also highly suggestive of endometriosis.

Peritoneal implants initially are small serosal lesions and usually escape detection. Larger, fibrotic implants of endometriosis are seen on MRI as spiculated nodules of very low signal intensity on T2-weighted images. [25, 26] These commonly occur in the cul-de-sac; they less commonly appear on the bladder dome, rectum, or umbilicus or in pelvic surgical scars. [25] Fat-saturated T1-weighted images are helpful to identify the punctate high signal intensity from hemorrhage in these lesions. [27, 28]

Cul-de-sac implants result in adhesions that constrict it. [29] Dilated fallopian tubes occasionally are seen on MRI in patients with endometriosis; these demonstrate high signal intensity on T1-weighted images, which is indicative of bloody fluid. [15, 30]

MRI can also demonstrate the complications of endometriosis, such as bowel implants and ureteral obstruction. [15] Since longer imaging times are required for MRI, antiperistaltic medication can improve visualization of the bowel.

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