Review of MRI imaging for placenta accreta spectrum: Pathophysiologic insights, imaging signs, and recent developments

Placenta Accreta Spectrum (PAS) refers to the range of abnormally adhesive and penetrative placental tissue at a uterine scar. PAS is divided into accreta, increta, and percreta based on degree of myometrial invasion. Its incidence has increased, and PAS is now the leading indication for emergency peripartum hysterectomy in the setting of catastrophic hemorrhage from a non-separating placenta. The recent release of the International Federation of Gynecology and Obstetrics (FIGO) guidelines in 2018 coupled with the joint consensus statement from the Society of Abdominal Radiology (SAR) and European Society of Urogenital Radiology (ESUR) in 2020 reflect decades worth of diagnostic and therapeutic advances in this field. Although the increasing role of MRI in PAS diagnosis is evident, the literature on PAS reveals several disparate but conceptually overlapping MRI signs. Identifying and differentiating between placenta increta and percreta on imaging may be quite challenging even with MRI and sometimes even on final pathology. In this review, we aim to (i) provide a clarified understanding of PAS pathophysiology, (ii) comprehensively review and classify MRI signs based on pathophysiologic underpinnings, (iii) highlight shortcomings in the current PAS literature; and (iv) highlight best practice guidelines for imaging diagnosis of PAS.