Placental magnetic resonance imaging Part II: placenta accreta spectrum

The human placenta remains an enigma to many. Its position as the point of communication between distinct maternal and fetal circulations means that it must act as both source of nourishment and gatekeeper for the developing pregnancy. In vivo assessment of the placenta is perhaps the greatest challenge, yet it is most essential for diagnostic and prognostic purposes. In particular, there is a need for improved diagnostic accuracy in recognizing the invasive forms of the placenta accreta spectrum that require surgical intervention at delivery and often cesarean hysterectomy. The costs of insufficient sensitivity and specificity are high, with well-documented cases of adverse outcomes ranging from unnecessary surgery to maternal hemorrhage and even death. In Part I of this pictorial essay series, we reviewed the appearance of the normal developing placenta across gestation by MRI. With this as a background, we here consider the varied appearances of the placenta accreta spectrum (placenta accreta, increta, percreta), which is a growing challenge given the rapidly expanding number of women worldwide with history of cesarean section delivery. Accurate prenatal imaging is crucial for recognizing cases of the placenta accreta spectrum and for planning the necessary surgery.