Ultrasound and MRI accordance and features in the prenatal diagnosis of placenta accreta

Objectives: To analyze major image features of ultrasonography and magnetic resonance imaging (MRI), as well as the agreement between the two methods for the diagnosis of placenta accreta. Methods: A retrospective analysis was performed on 378 highly suspected cases of placenta accreta in Obstetrics and Gynaecology Hospital of Fudan University, by comparing ultrasound and MRI results with postpartum surgical pathology and clinical follow-up results. Results: Clinical and postpartum pathology confirmed 65 cases of placenta accreta. Ultrasound and MRI results showed a high level of agreement (Kappa≈0.79). Ultrasound features with high accuracy (>60%) are as follows in the order of high to low: irregular blood flow signals in the basal portion of the placenta, intraplacental lacunae, placental thickening, thinning or disappearance of the hypoechoic retroplacental myometrial zone. The combination of the following three features has the largest Area Under Curve value (AUC, 0.93): Intraplacental lacunae, Thinning or disappearance of the hypoechoic retroplacental zone and Irregular blood flow signals in the basal portion of the placenta. MRI features with high accuracy (>60%) are as follows: Dark intraplacental bands on T2-weighted images, heterogeneous signal intensity within the placenta, blurring or disappearance of the lowsignal-intensity interface between the placenta and the myometrium. The combination of all 6 features listed in this article has the largest AUC (0.79). Conclusion: Ultrasonography, with a high accuracy, is still the main method for the diagnosis of placenta accreta. Combining multiple image features can improve the accuracy of diagnosis for both ultrasound and MRI.