Jauniaux, Eric; Jurkovic, Davor; Hussein, Ahmed M; Burton, Graham J; (2022) New Insights into the Etiopathology of Placenta Accreta Spectrum. American Journal of Obstetrics and Gynecology , 227 (3) pp. 384-391. 10.1016/j.ajog.2022.02.038.

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Abstract

Placenta accreta has been described as a spectrum of abnormal attachment of villous tissue to the uterine wall, ranging from superficial attachment to the inner myometrium without interposing decidua to transmural invasion through the entire uterine wall and beyond. These descriptions have prevailed for over 50 years and form the basis for diagnosis and grading of accreta placentation. Accreta placentation is essentially the consequence of uterine remodeling after surgery, primarily following cesarean section. Large cesarean scar defects in the lower uterine segment are associated with failure of normal decidualisation and loss of the sub-decidual myometrium. These changes allow placental anchoring villi to implant, and extravillous trophoblast cells to migrate, close to the serosal surface of the uterus. These microscopic features are central to the misconception that accreta placental villous tissue is excessively invasive, and have led to much confusion and heterogeneity in clinical data. Progressive recruitment of large arteries in the uterine wall i.e. helicine, arcuate and/or radial arteries results in high-velocity maternal blood entering the intervillous space from the first trimester of pregnancy, and subsequent formation of placental lacunae. Recently, guided sampling of accreta areas at delivery has enabled accurate correlation of prenatal imaging data with intraoperative features and histopathologic findings. In over 70% of samples, there are thick fibrinoid depositions between the tip of most anchoring villi and the underlying uterine wall and around all deeply implanted villi. The distortion of the utero-placental interface by these dense depositions and loss of the normal plane of separation is the main factor leading to abnormal placental attachment. These data challenge the classical concept that placenta accreta is simply due to villous tissue sitting atop the superficial myometrium without interposed decidua. There is also no evidence in accreta placentation that extravillous trophoblast is abnormally invasive or that villous tissue can cross the uterine serosa into the pelvis. It is the size of the scar defect, the amount of placental tissue developing inside the scar and the residual myometrial thickness in the scar area that determines the distance between the placental basal plate and the uterine serosa, and thus the risk of accreta placentation.

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