Imaging the Female Pelvis: When Should MRI be Considered?

Jennifer Hubert, MD; Diane Bergin, MD

Disclosures

Appl Radiol. 2008;37(1):9-24. 

In This Article

Leiomyomas

Leiomyomas, benign uterine neoplasms, are the most common tumor of the female genital tract. Their classifcation is based on their location within the uterine corpus as either intramural, submucosal, or subserosal. Most women are asymptomatic; however, the most common symptom is bleeding. Transvaginal ultrasound has been shown to be as effcient as MRI in the detection of the presence of myomas; however, MRI is superior in terms of mapping individual myomas.[18] This is especially true with larger uteri and with the presence of a large number of myomas.

On MRI, a uterus containing leiomyomas will be enlarged and will have an abnormal contour. On T2W images, leiomyomas appear as sharply marginated lesions of low signal intensity relative to the myometrium (Figure 9). Often, a high-signal-intensity rim can be identifed, more commonly in intramural or subserosal leiomyomas. Leiomyomas may contain calcifcations, especially in older women. Calcifed myomas can cause signifcant artifact on ultrasound and can obscure adjacent tissues. While similar calcifcation appears as a signal void on MRI, it typically does not limit the evaluation of adjacent tissues. On MRI, myomas larger than 3 to 5 cm are often heterogeneous because of various degrees of degeneration. Although varied, enhancement tends to be heterogeneous and less than that of the myometrium.[19,20,21]

Leiomyoma. (A) An axial T2-weighted image and (B) an axial T1-weighted 3-dimensional gradient-recalled echo postcontrast image show a myometrial low-T2-signal mass that is isointense to muscle on postcontrast images with a hypoenhancing rim, which is consistent with an enhancing leio myoma (arrowheads).

MRI is the modality of choice in evaluating leiomyomas before and after treatment with uterine artery embolization (UAE).[20,21] The use of MRI is optimal for pre-embolization assessment for delineating the location of leiomyoma and for accurately assessing pedunculated lesions. It is particularly useful in providing postembolization comparative images to assess whether there are persistent enhancing fbroids and to compare pre- and posttherapeutic size. Pre-embolization MRI may also be used to predict collateral feeding vessels by modifying protocol to optimize angiographic imaging. MRI can also identify or exclude the presence of other uterine abnormalities that may impact or preclude treatment.[22] Various studies have shown that certain preprocedural imaging characteristics may accurately predict response to UAE. High signal intensity on T1W sequences may indicate pre-existing hemorrhagic infarction, resulting in poor outcome secondary to insuffcient volume reduction. The degree of contrast enhancement has been shown to correlate with tumor response. A complete lack of contrast enhancement indicates nonviable tumor that will not respond to treatment.[22,23] After successful UAE, there is an overall reduction in uterine size and in mean leiomyoma volume. MRI characteristics that indicate a successful treatment include high signal intensity on T1W images and homogenously decreased T2 signal intensity. These fndings are suggestive of hemorrhagic infarction and correlate with a lack of contrast enhancement (Figure 10).[22,23,24] This lack of contrast enhancement has been shown to persist as far out as 3 years postembolization. Similarly, a lack of infarction at short-term follow-up will likely persist at long-term follow-up with MRI.

Post–uterine-artery-embolization imaging. (A) A sagittal T2-weighted fast spin-echo fat-suppressed image and (B) a sagittal T1- weighted 2-dimensional gradient-recalled echo postcontrast image shows multiple low-T2-signal myoma (arrowheads) that do not enhance following contrast, which is consistent with necrosis postembolization.

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