The purpose of this study was to evaluate the role of imaging in the management of pelvic masses seen during pregnancy and to assess the complementary role of magnetic resonance imaging (MRI) as an adjunct to ultrasound in the imaging of these masses in selected cases. We retrospectively reviewed imaging findings in pregnant patients with pelvic masses in the second trimester. Excluded were patients with unilocular cysts and fibroids. Sonographically, the masses were characterized as benign if the features were consistent with a septate cyst, a dermoid tumor, or an endometrioma. Patients with complex cystic masses, solid masses, or masses for which the organ of origin was indeterminate were recommended for additional MRI evaluation. There were a total of 20 masses in 18 pregnant patients, ranging in size from 3 to 15 cm, with a mean size of 7.8 cm. Ultrasound identified 12 benign lesions in 10 patients and suspicious or indeterminate masses in 8. Of these 8 patients, 7 underwent MRI evaluation. MRI characterized two masses as suspicious and five lesions as benign. Imaging findings resulted in three antepartum interventions. Ultrasound is useful at characterizing most pelvic masses in pregnancy. However, a small but significant number of masses may be sonographically suspicious or of indeterminate origin (i.e., adnexal versus uterine versus abdominal). In these instances, MRI, because of its superior lesion characterization and anatomic delineation of masses, is able to further reduce the number of patients that require intervention during pregnancy.
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