The rate of nonvisualization of the appendix on MRI is lower than US and reported to be 30.9% in a retrospective cohort study of 171 pregnant patients. Patients with nonvisualization of the appendix on MRI were more likely to be beyond the first trimester [40]. Evaluation for appendicitis with pelvic MRI in 51 pregnant patients for which a previous US did not demonstrate the appendix showed an overall sensitivity of 100%, a specificity of 93.6%, and a prevalence-adjusted PPV and NPV of 1.4% and 100%, respectively, with an accuracy of 94.0% [41]. Another recent study in 49 pregnant patients showed that in 88% of patients, appendicitis was ruled out, and surgery was prevented when MRI was performed after inconclusive US. MRI diagnosed all cases with acute appendicitis, with one case remaining inconclusive. The overall statistical performance of MRI shows a similar NPV of 100% with PPV of 83.3% [42]. Visualization of the normal appendix on MRI may be sometimes challenging. However, a retrospective study in 58 pregnant patients with suspected appendicitis showed that if MRI study was of sufficient diagnostic quality, with no ancillary signs of appendicitis, there were no cases of acute appendicitis. This was true despite the lack of visualization of the appendix in up to 50% of cases by at least 1 of 3 radiologists participating in the study. Therefore, if appendix is not visualized, the recommendation for interpretation is to word the report as low risk for appendicitis rather than indeterminate for excluding appendicitis [43]. The T1 bright appendix sign, defined as a high-intensity signal filling more than half the length of the appendix on T1-weighted imaging, was shown to be a specific sign for a normal appendix in a retrospective study of 125 pregnant patients. The sensitivity, specificity, PPV, and NPV are 44.9%, 95.5%, 97.6%, and 30.0%, respectively.
Acute Pelvic Pain in the Reproductive Age Group. The rate of nonvisualization of the appendix on MRI is lower than US and reported to be 30.9% in a retrospective cohort study of 171 pregnant patients. Patients with nonvisualization of the appendix on MRI were more likely to be beyond the first trimester [40]. Evaluation for appendicitis with pelvic MRI in 51 pregnant patients for which a previous US did not demonstrate the appendix showed an overall sensitivity of 100%, a specificity of 93.6%, and a prevalence-adjusted PPV and NPV of 1.4% and 100%, respectively, with an accuracy of 94.0% [41]. Another recent study in 49 pregnant patients showed that in 88% of patients, appendicitis was ruled out, and surgery was prevented when MRI was performed after inconclusive US. MRI diagnosed all cases with acute appendicitis, with one case remaining inconclusive. The overall statistical performance of MRI shows a similar NPV of 100% with PPV of 83.3% [42]. Visualization of the normal appendix on MRI may be sometimes challenging. However, a retrospective study in 58 pregnant patients with suspected appendicitis showed that if MRI study was of sufficient diagnostic quality, with no ancillary signs of appendicitis, there were no cases of acute appendicitis. This was true despite the lack of visualization of the appendix in up to 50% of cases by at least 1 of 3 radiologists participating in the study. Therefore, if appendix is not visualized, the recommendation for interpretation is to word the report as low risk for appendicitis rather than indeterminate for excluding appendicitis [43]. The T1 bright appendix sign, defined as a high-intensity signal filling more than half the length of the appendix on T1-weighted imaging, was shown to be a specific sign for a normal appendix in a retrospective study of 125 pregnant patients. The sensitivity, specificity, PPV, and NPV are 44.9%, 95.5%, 97.6%, and 30.0%, respectively.