Three-Dimensional Volume Rendering Ultrasound for Assessing Placenta Accreta Spectrum Severity and Discriminating it from Simple Scar Dehiscence

Background Prenatal ultrasound discrimination between Placenta Accreta Spectrum (PAS) and scar dehiscence with underlying non-adherent placenta is challenging both prenatally and intraoperatively which often leads to overtreatment. Also, accurate prenatal prediction of surgical difficulty and morbidity in PAS is difficult which precludes appropriate multidisciplinary planning. The advent of advanced three-dimensional volume rendering and contrast enhancement techniques in modern ultrasound systems provides a comprehensive prenatal assessment, revealing details that are not discernible in traditional 2D imaging. Objective To evaluate the use of three-dimensional volume rendering ultrasound techniques in determining the severity of PAS and distinguishing between PAS and scar dehiscence with underlying non-adherent placenta. Study design A prospective, cohort study was conducted between July 2022 and July 2023 in the fetal medicine unit of Dr Soetomo Academic General Hospital, Surabaya, Indonesia. All pregnant individuals with anterior low-lying placenta or placenta previa with a previous caesarean section that were referred with suspicion of PAS were consented and screened using the standardised 2-dimensional (2D) and Doppler ultrasound imaging. Additional 3D volumes were obtained from the sagittal section of the uterus with a filled urinary bladder. These were analysed by rotating the region of interest to be perpendicular to the uterovesical interface. The primary outcomes were the clinical and histological severity in the cases of PAS and correct diagnosis of dehiscence with non-adherent placenta underneath. The strength of association between ultrasound and clinical outcomes were determined. Multivariate logistic regression analyses and diagnostic testing of accuracy were used to analyse the data. Results A total of 70 patients (56 with PAS and 14 with scar dehiscence) were included in the analysis. Multivariate logistic regression of all 2D and 3D signs revealed the 3D loss of clear zone (p < 0.001) and the presence of bridging vessels on 2D Doppler ultrasound (p = 0.027) as excellent predictors in differentiating scar dehiscence and PAS. The 3D loss of clear zone demonstrated a high diagnostic accuracy with an area under the curve (AUC) of 0.911 (95% CI 0.819 – 1.002), with a sensitivity of 89.3% (95% CI 78.1 – 95.97%) and specificity of 92.9% (95% CI 66.1 – 99.8%). The presence of bridging vessels on 2D Doppler demonstrated an AUC of 0.848 (95% CI 0.714 – 0.982) with a sensitivity of 91.1% (95% CI 80.4 – 97.0%) and specificity of 78.6% (95% CI 49.2 – 95.3%). A subgroup analysis among the PAS group revealed that the presence of a 3D disrupted bladder serosa with obliteration of the vesicouterine space was associated with vesicouterine adherence (p <0.001). Conclusion 3D volume rendering ultrasound is a promising tool for effective discrimination between scar dehiscence with underlying non-adherent placenta and PAS. It also shows potential in predicting the clinical severity with urinary bladder involvement in cases of PAS.