Clinical utility of magnetic resonance imaging in the evaluation of pregnant females with suspected acute appendicitis.

OBJECTIVES: To assess the diagnostic performance of magnetic resonance imaging (MRI) in a large cohort of pregnant females with suspected acute appendicitis and to determine the frequency of non-appendiceal causes of abdominal pain identified by MRI in this population.

METHODS: This HIPAA compliant, retrospective study was IRB-approved and informed consent was waived. 212 MRI exams were performed consecutively on pregnant women aged 17-47 years old suspected of having acute appendicitis; eight exams were excluded and analyzed separately due to equivocal findings or lack of clinical follow up. Radiology reports for the MRI and any preceding ultrasound exams were reviewed as well as the patients' electronic medical record for surgical, pathological, or clinical follow up.

RESULTS: Fifteen (7.3%) of 204 MRI scans were determined to be positive for appendicitis, 14 of which were proven on surgical pathology, and one was found to have ileocecal diverticulitis. Out of the remaining 189 scans, none were subsequently shown to have acute appendicitis either surgically or based on clinical follow up. Negative predictive value (NPV) was 100% and positive predictive value was 93.3%. Sensitivity and specificity were 100% and 99.5%, respectively. Non-appendiceal findings which may have accounted for the patient's abdominal pain were seen in 91 (44.2%) of 189 scans. The most common extra-appendiceal causes of abdominal pain identified on MRI include degenerating fibroids (n = 11), significant hydronephrosis (n = 12), cholelithiasis (n = 6), and pyelonephritis (n = 3).

CONCLUSION: Our large study cohort of pregnant patients confirms MRI to be of high diagnostic value in the workup of acute appendicitis with 100% NPV and sensitivity and 99.5% specificity. Furthermore, an alternative diagnosis for abdominal pain in this patient population can be made in nearly half of MRI exams which are deemed negative for appendicitis.