EP16.06: Ultrasound dilemmas: the diagnostic challenge in detecting posterior placenta accreta

Placenta accreta spectrum (PAS) disorders encompass severe iatrogenic complications. Among patients with clinical suspicion of PAS, ultrasound is the first line imaging done to determine degree of invasion and location. While ultrasound has shown enhanced diagnostic accuracy in anterior PAS, its accuracy in detecting posterior PAS is lower. Unlike anterior PAS, where a prior Caesarean section scar is a crucial anatomical condition for placental invasion, posterior PAS demonstrates a weaker association and is linked with prior uterine surgeries. Diagnosing posterior PAS becomes challenging when there are no identifiable risk factors or sonographic findings. A 27-year-old G5P3 (3013) at 33 weeks and 5 days gestation, with three prior Caesarean sections and no history of myomectomy or curettage, presented with vaginal spotting. This lead to a clinical suspicion of placenta previa with potential anterior placenta accreta. On ultrasound, there were no sonographic features of placenta accreta, but noted a symmetrically implanted placenta on the lower segment, completely covering the os. A classical Caesarean section with hysterectomy was done due to vaginal bleeding and a posteriorly adherent placenta. Histopathological examination confirmed the diagnosis of posterior placenta accreta. Detecting posterior PAS prenatally is challenging compared to anterior PAS. Risk factors associated with anterior placental invasion, such as previous Caesarean sections, may not be as relevant for posterior placental invasion. This case emphasises the limitations of ultrasound in detecting posterior PAS and advocates MRI for further evaluation in high-risk cases. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.