Jauniaux, E; Hussein, AM; Elbarmelgy, RM; Elbarmelgy, RA; Burton, GJ; (2022) Failure of placental detachment in accreta placentation is associated with excessive fibrinoid deposition at the utero-placental interface. American Journal of Obstetrics and Gynecology , 226 (2) 243.e1-243.e10. 10.1016/j.ajog.2021.08.026.

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Abstract

BACKGROUND: The main histopathologic diagnostic criteria for the diagnosis of placenta accreta has been for over 80 years the finding of a direct attachment of the villous tissue to the superficial myometrium or adjacent to myometrial fibres without interposing decidua. There have been very few detailed histopathologic studies in pregnancies complicated by placenta accreta spectrum (PAS) disorders and our understanding of the pathophysiology of the condition remains limited. OBJECTIVE: To prospectively evaluate the microscopic changes used in grading and to identify changes that might explain the abnormal placental tissue attachment. MATERIAL AND METHODS: Forty consecutive cesarean hysterectomy specimens for placenta previa accreta at 32-37 weeks of gestation with at least one histological slide showing deeply implanted villi were analysed. Prenatal ultrasound examination included placental location, myometrial thickness, subplacental vascularity and lacunae. Macroscopic changes of the lower segment were recorded during surgery and areas of abnormal placental adherence were sampled for histology. Seven hysterectomy specimens with placenta in-situ from the Boyd Collection at 20.5 – 32.5 weeks were used as controls. RESULTS: All 40 patients had a history of at least two prior cesarean deliveries and presented with a mainly anterior placenta previa. Thirty-seven (92.5%) cases presented with increased subplacental vascularity, 31 (77.5%) cases with myometrial thinning and all with lacunae. Twenty (50%) cases presented with subplacental hypervascularity, lacunae score 3+ and lacunae feeder vessels. Intraoperative findings included anterior lower segment wall increased vascularisation in 36 (90.0%) cases and extended area of dehiscence in 18 (45.0%) cases. Immediate gross examination of hysterectomy specimens showed an abnormally attached areas involving up to 30% of the basal plate, starting at < 2 cm from the dehiscence area in all cases. Histologic examination found deeply implanted villi in 86 (53.8%) samples with only 17 samples (10.6%) presenting with villous tissue reaching at least ½ the uterine wall thickness. There were no villi crossing the entire thickness of the uterine wall. There was microscopic evidence of myometrial scarification in all cases. Dense fibrinoid deposits, 0.5-2 mm thick, were found at the utero-placental interface in 119 (74.4%) of the 160 samples between the anchoring villi and the underlying uterine wall at the accreta areas and around all deeply implanted villi. In controls, the Nitabuch’s stria and basal plate became discontinuous with advancing gestation and there was no evidence of fibrinoid deposition at these sites. CONCLUSION: Samples from accreta areas at delivery present with a thick fibrinoid deposition at the utero-placental interface on microscopic examination independently of deeply implanted villous tissue in the sample. These changes are associated with distortion of the “Nitabuch’s membrane” and might explain the loss of parts of the physiological site of detachment of the placenta from the uterine wall in PAS. These findings also indicate that accreta placentation is more than direct attachment of the villous tissue to the superficial myometrium and support the concept that accreta villous tissue is not truly invasive.

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