Is There a Role for MRI in the Management of Placenta Accreta Spectrum?

The diagnosis of placenta accreta spectrum (PAS) is based on evaluation of risk factors and imaging findings. Ultrasound (US) is widely available and relatively cheap; magnetic resonance imaging (MRI) is expensive and not universally available. We review performance, interpretation, accuracy, and pitfalls of MRI, and whether it has a role in the management of PAS.

Recent meta-analyses showed excellent diagnostic accuracy in depth of placental invasion. Specific MRI features (intraplacental T2 dark bands, myometrial disruption, uterine bulge, and uteroplacental or parametrial hypervascularity) were shown to have significant association with clinical outcomes. The presence of at least three MRI signs was associated with complicated delivery; the presence of six or more MRI signs was associated with massive bleeding, hysterectomy, or extensive bladder repair.

MRI is performed on patients with high suspicion for PAS based on risk factors and abnormal US findings. Thus, the pretest probability is very high, artificially inflating sensitivity and specificity. The FIGO consensus recommendation states that MRI is not essential for diagnosis of PAS. When selectively performed, and interpreted by experts, it may be useful in evaluation of areas difficult to see on US and in determining the full extent of placenta percreta. Imaging findings should be reviewed together with clinical information, an attempt made to reconcile any differences in interpretation, and if findings remain discordant, management should err on the side of the most severe assessment of this highly morbid condition which can lead to maternal mortality if unrecognized.