MR imaging evaluation of acute appendicitis in pregnancy

Purpose: To retrospectively assess the diagnostic performance of magnetic resonance (MR) imaging in pregnant patients suspected of having acute appendicitis. Materials and Methods: The study was approved by the committee on clinical investigations and was HIPAA compliant. The informed consent requirement was waived. MR images were obtained in 51 consecutive pregnant patients (mean age, 28.3 years) who were clinically suspected of having acute appendicitis. In this protocol for pregnant patients, MR imaging is performed when findings at ultrasonography (US) are inconclusive or additional information is needed. Four patients had appendicitis, which was confirmed at surgery in three patients and at follow-up computed tomography in one patient. Initial interpretations were used for patient care and to calculate diagnostic accuracy. The appendix was considered normal at MR imaging if its diameter was less than or equal to 6 mm or if it was filled with air, oral contrast material, or both. An enlarged fluid-filled appendix (>7 mm in diameter) was considered an abnormal finding. An appendix with a diameter of 6-7 mm was considered an inconclusive finding; in those cases, the presence of periappendiceal inflammation was used for the final diagnosis. Three radiologists retrospectively assessed the visualization of the appendix by using a 5-point scale. Statistical analysis was performed by using the median and Fisher exact tests and the Spearman correlation coefficient. Results: MR images were positive for appendicitis in four patients and inconclusive in three. In the three patients with inconclusive results, the appendix was not seen in two patients and was borderline enlarged (7 mm in diameter) in the third. The overall sensitivity, specificity, prevalence-adjusted positive and negative predictive values, and accuracy for MR imaging was 100%, 93.6%, 1.4%, 100%, and 94.0%, respectively. Conclusion: MR imaging is an excellent modality for use in excluding acute appendicitis in pregnant women who present with acute abdominal pain and in whom a normal appendix is not visualized at US.