Comparing 3D models of placenta accreta spectrum to surgical findings.

OBJECTIVE Placenta accreta spectrum (PAS) is associated with significant maternal morbidity mainly related to blood loss. Pre-operative planning is aided by antenatal ultrasound and Magnetic Resonance imaging (MRI). We sought to assess whether three dimensional (3D) models from MRI images were accurate when compared with surgical and pathological findings. METHODS DICOM files containing MRI images with varying severity of PAS (n=4) were modelled using 3D Slicer. Placenta, bladder and myometrial defects were modelled. Myometrial defects at three different uterine locations were included - anterior, lateral and inferior. 3D models were used to identify the relationship between the myometrial defect and the internal cervical os. Findings were validated in a larger series of PAS cases (n=14) where patterns of invasion were compared to estimated blood loss and distance from defect to the internal os. RESULTS The defect illustrated in the four 3D models correlates to both surgical and pathological findings in terms of depth and pattern of invasion, location of defect, bladder involvement. Blood loss and topography of the defect from 3D modelling were examined in fourteen further cases. Inferior defects were associated with increased blood loss compared to anterior defects. Increased distance from cervix was associated with reduced blood loss (R2 0.352, P=0.01). CONCLUSION 3D models of PAS provide an accurate preoperative description of placental invasion and should be investigated as a tool for selecting patients for uterine conserving surgery.