Comparing the diagnostic performance of MRI versus CT in the evaluation of acute nontraumatic abdominal pain during pregnancy.

The objectives of this study were to document the utilization of MRI compared with CT in pregnant patients presenting with acute nontraumatic abdominal pain at our institution and to compare the diagnostic performance of the two modalities. A retrospective review identified all pregnant patients at our institution who had MRI or CT exams of the abdomen and/or pelvis for acute nontraumatic abdominal pain over a 3-year period from January 2008 through December 2010. The imaging diagnoses were compared with pathologic data or operative findings as the primary reference standard or with clinical follow-up and laboratory data as the secondary reference standard. Patients without surgically proven diagnoses were followed clinically until delivery, when possible. Ninety-four pregnant patients were included in this study: 61 MRI exams were performed in 57 patients, 44 CT exams were performed in 43 patients (including six patients who had both), and 72 patients (77 %) had ultrasound prior to cross-sectional imaging, with the appendix specifically assessed in 25 patients but visualized in only two of them. Of 61 MRI exams, 24 were considered positive for imaging diagnoses, 33 were negative, and 4 were equivocal. Of 44 CT exams, 24 were positive and 20 were negative. The test characteristics for MRI and CT in the diagnosis of acute abdominal pain were as follows: sensitivity 91 and 88 %, specificity 85 and 90 %, positive predictive value 81 and 91 %, negative predictive value 94 and 8 5 %, and diagnostic accuracy 88 and 88 %, respectively. Differences were not statistically significant (p value = 1). The majority of MRIs (34/61 = 56 %) were read by emergency radiologists. MRI and CT performed equally well in the evaluation of acute nontraumatic abdominal pain during pregnancy. Given its lack of ionizing radiation, MRI may be preferable. Given that the majority of MRIs were read by radiologists specializing in emergency imaging, this is a technique that emergency radiologists should be comfortable interpreting.