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Tumor masses in distant organs or anatomic sites

1 T2-weighted or contrast-enhanced T1-weighted images.

2 Modified from [26]

Fig. 5. Endometrial cancer: stage IB. Sagittal (a) and coronal (b) T2 FSE of the uterus with distended heterogeneous endometrial canal. The tumor myometrial interface is irregular, a sign of superficial invasion or deep, > 50%, depending on penetration into the underlying myometrium.

Current recommendations for MR imaging in women with endometrial cancer include instances where:

- There is a high pretest probability for lymph node metastases (e.g., high grade tumor, papillary or clear cell tumor) (CT is equivalent)

- There is a high pretest probability for cervical invasion

- There is a need for multi-factorial assessment of my-ometrial, cervical and lymph node involvement.

The Ovary

The main role of MRI in evaluating ovarian abnormalities is that of tissue characterization [43, 44]. MRI is a problem-solving tool for determining the origin of a mass and providing information on its make-up.

Benign Conditions

The most commonly encountered benign ovarian condition is physiologic cysts. These are round, smooth-walled and lack solid elements or debris. These simple cysts are low in SI on T1-W sequences and get progressively higher in SI on T2-W images. Hemorrhagic cysts, which contain methemoglobin, tend to have high SI intensity on both T1- and T2-W sequences, whereas endometriomas are multilocular masses that are high in SI on T1-W sequences and show shading on T2-W sequences [45, 46] (Fig. 6). This shading reflects rebleeding into the cysts and consequently the presence of blood products of varying chronicity. T1-W fat-suppressed sequences improve the conspicuity of endometriomas [47, 48]. In one study, the sensitivity and specificity for detecting endometri-omas > 1 cm was 91% and 94%, respectively [49]. T1-W fat suppressed sequences also help differentiate fat-containing lesions (e.g., cystic teratomas) from blood-containing lesions [50] (Fig. 7).

Malignant Conditions: Ovarian Carcinoma

The sensitivity of MR for detecting adnexal pathology parallels that of US and CT, ranging from 87-100%. However, it is the tissue characterization potential of MRI that makes it robust for evaluating the adnexa [51]. In fact, for characterizing an ovarian mass as benign or malignant the accuracy of MR ranges from 8395% compared to US and CT, which range from 5388% and 66-94%, respectively [52-54]. In the largest prospective trial evaluating ovarian masses imaged with transvaginal sonography, MRI was more accurate than CT or Doppler sonography for diagnosing malignancy [55]. Once the diagnosis of malignancy is made, CT of the abdomen and pelvis is typically performed. The accuracy of CT and MR staging is comparable, approaching 90% [56]. Neither modality can supplant staging laparotomy because of their limited ability to detect small intraperitoneal implants, although MRI

Fig. 6. Endometriomas. Axial T1 without fat supression (a), T1 with fat suppression (b) and T2 FSE (c) of bilateral ovarian masses that retrain high signal intensity on the T1 fat-suppressed technique and demonstrate loss of signal shading, on T2 FSE

may aid surgical treatment planning. MRI is also adept at identifying patients with bulky non-resectable disease and can spare patients the morbidity of surgical staging. The positive and negative predictive values for

Fig. 7. Dermoid. Axial T1 without fat suppression, and T1 with fat suppression, of left ovarian mass. High signal intensity elements on T1 image without fat suppression fall in signal with the addition of chemically selective fat suppression

diagnosing non-resectability are 91% and 97%, respectively [57].

Ovarian cancers are typically large heterogeneous masses with both cystic and solid components (Fig. 8). Owing to their complexity, their SI on T1 and T2-W sequences is variable. Rather than predicting the exact histology of an ovarian cancer, the real strength of MRI is in suggesting whether or not a lesion is malignant. Both primary and ancillary criteria have been formulated for this determination. These criteria are up to 95% accurate in correctly characterizing an adnexal mass as benign or malignant [52]. Primary criteria include size greater than 4 cm, solid or predominantly solid lesion, wall thickness greater than 3 mm, septae greater than 3 mm, nodularity, and presence of necrosis. Ancillary criteria include involvement of pelvic organs or sidewall, peritoneal, mesenteric or omental disease, ascites and lymphadenopathy.

Fig. 8. Ovarian cancer. Axial (a) and sagittal (b) T2 SSFSE and sagittal gadolium-enhanced T1 with fat suppression (c) of complex ovarian mass. Incidental note is made of large anterior uterine corpus leiomyoma

Results of a multivariate analysis found that necrosis within a solid lesion, vegetations within a cystic lesion, ascites and peritoneal metastases are the features most predictive of malignancy [52].

Current imaging recommendations for MRI of the ad-nexa include:

- Evaluation of an equivocal or non-diagnostic transvaginal sonogram

- Characterization of a known ovarian mass

- Determination of resectability in women with the diagnosis of ovarian cancer.

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