Uterine layers hypervascularization in atypical placentation: the comparison of magnetic resonance imaging with vascular pathomorphology

Abstract

Rationale: One in five women worldwide delivers through cesarean section, which is associated to a high rate of placenta previa and abnormal placenta attachment to the uterine wall. The grade of placenta accreta spectrum (PAS) correlates with blood loss volume, which could be related to vascularization characteristics. Up to now, there have been no studies on the diagnostic value of magnetic resonance criteria for hypervascularization of the uterine wall and their correlation with an assumed grade of PAS according to the International Federation of Gynecology and Obstetrics (FIGO) classification. Also, abnormal vessels location and their wall structure have not been studied with state-of-the-art pathomorphological methods. Aim: To develop a classification for various types of the uterine wall hypervascularization depending on the depth of placental invasion assessed by magnetic resonance imaging (MRI). Methods: We retrospectively analyzed medical files of 66 patients aged 18 to 45 years, who were assumed to have PAS based on their sonography results. To clarify the extent and localization of the placental invasion, all patients had MRI performed at 24 to 32 weeks of gestation. In all patients, the PAS grade was verified pathologically; in 30 of them (45,5%), a detailed pathological examination was additionally performed. The PAS grades were classified according to Morbidly Adherent Placenta Imaging Reporting and Data System (MAPI-RADS). The MRI data were correlated with the PAS (FIGO) grade estimated from intraoperative data and with intraoperative blood loss. At the final study step, the MRI data was correlated with abnormal pathomorphology, with the assessment of the degree of vascularization and the visual picture of abnormal uteroplacental vasculature. Results: We have proposed a classification of MRI signs of hypervascularization in the lower uterine segment correlating with the depth of placenta accreta. Type 1. Single small vessels in the myometrium, medium caliber arteries in the projection of the uterine serosa (normal variation for the 3rd trimester of gestation). Type 2. Numerous small confluent vessels, mainly in the uteroplacental region, and retroplacental hematomas (typical for placenta accreta, or FIGO PAS 1). Type 3. Intrauterine hypervascularization with a deficient myometrium thickness, predominantly vessels of the middle layer (typical for placenta increta, or FIGO PAS 2). Type 4. Thinning of the lower uterine segment due to significant bulging of the placenta in the presence of curved anastomosing vessels of vast caliber over 4 mm (typical for placenta increta – FIGO PAS 2, as well as placenta percreta – FIGO PAS 3a). Type 5. Hypervascularization outside the uterus, over its surface and in the parametrial tissues: at the border with the bladder, uterine isthmus, including signs of fibrosis and growing into the posterior bladder wall (typical for various grades of placenta percreta – FIGO PAS 3b, 3c). Conclusion: The proposed classification of uterine wall hypervascularization in accordance with the grades of placenta accreta spectrum (FIGO PAS) could be useful for its practical implementation by radiologists.