MRI as an alternative to CT after inconclusive ultrasound in subacute/acute abdominal pain in young women: a prospective multicenter noninferiority study

Abstract

Objective: To assess the noninferiority of MRI diagnostic accuracy to CT scan as a second-line examination of acute/subacute abdominopelvic pain in a population of young women after an inconclusive ultrasound (US). Methods: This prospective, multicenter non-inferiority study included 18–40-year-old non-pregnant women with non-traumatic acute/subacute abdominal pain. They had an inconclusive US warranting the prescription of an additional CT scan. Within 6 h of the CT, all these women underwent abdomino-pelvic MRI. A retrospective reading of the CT and MR provided a diagnosis using a standardized list. The gold standard diagnosis, based on a 3-month follow-up, was done by a panel of experts. Statistical analysis was conducted to assess the noninferiority of the diagnostic accuracy of MRI compared to that of CT. The noninferiority margin was set at 10%. Inter-observer agreement and diagnostic performance of a conditional imaging strategy were estimated. Results: 133 participants were analyzed (median: 27 years). The most common diagnoses were non-specific pain (30.1%), ovarian cyst rupture (12.8%), and appendicitis (9.7%). MRI demonstrated non-inferiority diagnostic accuracy estimated between 60.9% (81/133) and 88% (117/133) compared to CT, estimated between 64.7% (86/133) and 83.5% (111/133). The conditional imaging strategy (MRI, followed by CT when the MRI was normal) had a diagnostic accuracy of 91%. Conclusion: MRI diagnostic performances are not inferior to CT for acute abdominal pain in women aged 18–40. A conditional imaging strategy based on MRI would give an accuracy of 91% and might be considered a second-line imaging modality in that context. Key Points: Question Can MRI serve as an alternative to CT as a second-line imaging modality for acute abdominopelvic pain in young women (18–40) after an inconclusive ultrasound? Findings MRI accuracy after inconclusive US ranged from 60.9 to 88%. A conditional strategy (MRI first, CT if normal) reached 91% accuracy, avoiding 59% of CTs. Clinical relevance MRI is not inferior to CT for diagnosing uncategorized causes of acute abdomino-pelvic pain in young non-pregnant women. A conditional imaging strategy based on MRI as a second-line imaging modality would give an accuracy of 91%.