Structural failure sites in posterior vaginal wall prolapse: stress 3D MRI-based analysis

Introduction and hypothesis The objective was to identify structural failure sites in rectocele by comparing women with and those without posterior vaginal wall prolapse and accessing their relative contribution to rectocele size based on stress MRI-based measurements. Methods We studied three-dimensional stress MRI at maximal Valsalva of 25 women with (cases) and 25 without (controls) posterior vaginal prolapse of similar age and parity. Vaginal wall factors (posterior wall length and width); attachment factors (paravaginal posterior wall location, posterior fornix height, and perineal height); and hiatal factors (hiatal size and levator ani defects) were measured using Slicer 4.3.0 (R) and a custom Python program. Stepwise linear regression was used to assess the relative contribution of all factors to the posterior prolapse size. Results We identified three primary factors with large effect sizes of 2 or greater: two attachment factors-posterior paravaginal descent and perineal height; and one hiatal factor-genital hiatus size. These were the strongest predictors of the presence and size of rectocele, the most common failure sites, found in 60-76% of cases; and highly correlated with one another (r = 0.72-0.84, p < .001). Longer vaginal length, wider distal vagina, lower posterior fornix, and larger levator ani hiatus had smaller effect sizes and were less likely to fall outside the norm (20-24%) than the three primary factors. When considering all the supporting factors, the combination of perineal height, posterior fornix height, and vaginal length explained 73% of the variation in rectocele size. Conclusions Lower perineal and lateral posterior vaginal location and enlarged genital hiatus size were strong predictors of rectocele occurrence and size and correlated highly.