Role for MRI in Secondary Screening for Placenta Accreta

Aims/Background Rates of both placenta praevia and placenta accreta spectrum (PAS) are rising. There is significant morbidity associated with PAS and antenatal detection reduces morbidity at delivery. In the UK there is a move to centralise care of these cases in dedicated units. Incidental diagnosis is more common, in the absence of a regular screening program. In non-specialist hospitals, there is a need to consider adjunct confirmatory diagnostics prior to referral to specialist centres. This is important to ensure capacity management in specialist centres. Ultrasound (US) and Magnetic Resonance Imaging (MRI) have both been used to diagnose PAS with high levels of accuracy with experienced operators. The role of MRI as an adjunct with US has not been clearly defined but is often requested. Methods A retrospective analysis of all cases referred for MRI as a secondary modality after US to evaluate possible PAS. A total of 41 cases had MRI performed over 13 years with a trend of increasing demand over time. Results The series identified eleven cases of PAS. MRI demonstrated a high level of accuracy, similar to published literature (sensitivity 81.8%, Specificity 86.6%) and correctly reclassified 2 cases as PAS, which were considered normal on US. There were 2 cases of PAS which were missed by both US and MRI. Conclusion This series demonstrates increasing demand in our trust for MRI over the period of the study. The addition of MRI as a second test improved accuracy compared to ultrasound alone. MRI has a role in secondary screening for PAS in non-specialist units.