818 MRI Markers of PAS in Individuals Without PAS

The imaging diagnosis of placenta accreta spectrum (PAS) is challenging. Ultrasound markers of PAS are often seen in unaffected individuals but the prevalence of MRI markers in unaffected pregnancies is unknown. We evaluated the prevalence of MRI PAS markers in patients without PAS. Retrospective analysis of MRIs performed at greater than 20 weeks gestation for non-PAS indications at a single institution from Jan 2019 to June 2022. Our institution obtains placental evaluation sequences for all MRIs obtained during pregnancy. Individuals with clinical or pathologic PAS or missing delivery data were excluded. Three experienced radiologists blinded to patient history, independently assessed for 11 markers of PAS as defined by the Society of Abdominal Radiology and the European Society of Urogenital Radiology guidelines. The prevalence of markers was compared between patients with and without a prior cesarean. Ten percent of cases were examined by all radiologists for consistency. 171 MRIs performed at a median GA of 29 weeks (IQR 6.3 weeks) were included. 3.5% of fetuses were confirmed genetically abnormal and 66% had normal aneuploidy testing. At least one marker of PAS was seen in 86.5% of MRIs. The most prevalent markers were placental heterogeneity (51.5%), dark intraplacental bands on T2 weighted images (39.8%), loss of the retroplacental T2-hypointense line (36.8%), myometrial thinning (33.9%), and abnormal vascularization of the placental bed (32.2%). Three markers were uncommon: placental bulge (1.2%), placental ischemic infarction (1.2%), and focal exophytic mass (0%). Myometrial thinning was significantly more likely to be seen in those with a prior cesarean section than those without (55.2% vs 29.6%, p=0.008). Similar to ultrasound, MRI markers of PAS are frequently seen in patients without PAS. Overreliance upon these markers in isolation is likely to lead to overdiagnosis of PAS.