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

Hemorrhagic Ovarian Cyst and Endometrioma

With its high contrast resolution and its tissue characterization capabilities, MRI is a valuable tool for the characterization of echogenic adnexal masses detected by ultrasound. The accuracy of MRI for identifying lesions such as hemorrhagic cysts and endometriomas is higher than with transvaginal ultrasound imaging. On ultrasound, these lesions are occasionally misinterpreted as solid tumors, mature cystic teratomas, or complex cysts.[5,6,7,8]

Most ovarian cysts are functional in origin and occasionally can be complicated by intracystic hemorrhage. The MRI characteristics can be variable in this situation, depending on the age and amount of the hemorrhagic component. In general, however, they tend to be of relatively high signal intensity on T1W images and of intermediate-to-high signal intensity on T2W images and frequently reveal a fluid-fluid level (Figure 1). Hemorrhagic cysts should remain of relatively high signal on T1W images with fat suppression, which helps to differentiate them from dermoid cysts in most situations. They also tend to have thicker walls than do simple cysts and may exhibit wall enhancement on postcontrast images.

Hemorrhagic cyst. (A) An axial T2-weighted image, (B) an axial T1-weighted (T1W) gradient-recalled echo (GRE) fat-suppressed image, and (C) an axial T1W GRE fat-suppressed postcontrast image show an adnexal lesion with high T1 and intermediate T2 signal that is consistent with a hemorrhagic ovarian cyst (arrowheads) with fluid-fluid level.

However, the internal components of the cysts should never enhance. The majority of hemorrhagic ovarian cysts may be accurately diagnosed by ultrasound. MRI, however, should be considered when the hemorrhagic cystic lesion persists or increases in size on follow-up ultrasound.

Endometriosis is the ectopic presence of functional endometrial glands and stroma outside the uterus. Although laparoscopy remains the standard for diagnosing and staging pelvic endometriosis, MRI can identify lesions obscured at laparoscopy by dense ad hesions. MRI has a sensitivity of 90%, a specifcity of 98%, and an overall accuracy of 96% for the identifcation of endometriomas in patients with clinically suspected adnexal masses.[8,9,10] As with hemorrhagic cysts, the MRI appearance of endometriomas is somewhat variable based on the stage and amount of blood products. They are typically of high signal on T1W images and of intermediate-to-low signal intensity on T2W images (Figure 2). This relatively lower signal intensity on T2W imaging, which is often referred to as "T2-shading," is secondary to methemoglobin, protein, and iron from repeated episodes of hemorrhage. Endometriomas are more frequently bilateral and usually exhibit multiplicity. Endometriosis implants on serosal or peritoneal surfaces are identifed on MRI by high T1 signal seen on nonenhanced fat-suppressed images.

Endometriosis. (A) An axial T2-weighted (T2W) fast spin-echo image, (B) a precontrast axial T1-weighted (T1W) fat-suppressed 3-dimensional (3D) gradient-recalled echo (GRE) image, and (C) a postcontrast axial T1W fat-suppressed 3D GRE image show bilateral adnexal hemorrhagic lesions (arrowheads), which are consistent with endometriomas with low-signal “shading' on the T2W image and high signal on the T1W images without internal enhancement.

In diagnosing ovarian torsion, a true gynecologic emergency ultrasound is the modality of choice. If sonographic results are equivocal, however, MRI may be performed. Ovarian torsion is usually the consequence of an underlying ovarian lesion, most commonly dermoid or parovarian cysts.[9] As with hemorrhagic cysts and endometriomas, the presence of hemorrhage leads to a variable appearance that can be further complicated by the presence of infarction. Findings on MRI that suggest ovarian torsion include deviation of the uterus toward the affected side, engorgement of blood vessels toward the affected side, and a small amount of ascites. Findings that indicate a twisted adnexal tumor include protrusion of the lesion to the affected side, thick straight blood vessels draping over the lesion, and complete absence of enhancement.

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