Pelvic masses in pregnancy: MR imaging.

The value of magnetic resonance (MR) imaging was assessed for 17 pregnant patients with sonograms suggestive of a pelvic mass. The MR imaging signal features improved lesion characterization in 47% (eight of 17) of cases, including two of four mature cystic teratomas of the ovary, three uterine fibroids, one solid ovarian tumor, one endometrioma, and a distended urinary bladder that had been mistaken for an ovarian cystic mass. Both MR imaging and sonography were accurate for the characterization of three ovarian cystadenomas and two simple ovarian cysts. On both MR images and sonograms, two simple ovarian cysts were incorrectly diagnosed as complex cystic masses and one teratoma was incorrectly diagnosed as a simple cyst. The origin of the pelvic mass (13 in the ovary, three in the uterus, and one distended urinary bladder) was accurately determined on 100% (17 of 17) of the MR images versus 71% (12 of 17) of the sonograms. In three cases, the results of MR imaging led to cancellation of surgery, which would have proceeded on the basis of the sonographic results alone. MR imaging is a valuable complement to sonography for preoperative evaluation of pelvic masses in pregnant patients.