Magnetic resonance imaging findings in placenta accreta spectrum disorders: pictorial essay

Placenta accreta spectrum disorders are characterized by abnormal adhesion of the placenta that can be subdivided into three categories according to degree of invasion: placenta accreta (passing through the decidua basalis and adhering to the myometrium); placenta increta (penetrating the myometrium); and placenta percreta (invading the uterine serosa or adjacent tissues or organs). The incidence of placenta accreta has increased significantly in recent decades, mainly because of an increase in the rates of cesarean section, which is its main risk factor. Accurate prenatal identification makes it possible to institute the ideal treatment with a multidisciplinary team, significantly minimizing maternal morbidity and mortality. The examinations of choice are ultrasound and magnetic resonance imaging (MRI). When the ultrasound evaluation is inconclusive, as well as when the patient has risk factors for the condition or the placenta is in a posterior location, MRI is indicated. In cases of placental invasion of the adjacent pelvic organs, MRI is also preferable because it provides a broader field of view, which improves surgical planning. Numerous features of placenta accreta spectrum disorders are discernible on MRI, including dark intraplacental bands, uterine bulging, and heterogeneous placenta. Knowledge of these findings and the combination of two or more of them increase confidence in the diagnosis.