Pelvic cross-sectional area at the level of the levator ani and prolapse

Intraabdominal pressure acts on the pelvic floor through an aperture surrounded by bony and muscular structures of the pelvis. A small pilot study showed the area of the anterior portion of this plane is larger in pelvic organ prolapse. We hypothesize that there is a relationship between prolapse and anterior (APA) and posterior (PPA) pelvic cross-sectional area in a larger, more diverse population.

MRIs from 30 prolapse subjects and 66 controls were analyzed in this case-control study. The measurement plane was tilted to approximate the level of the levator ani attachments. Three evaluators made measurements. Patient demographic characteristics were compared using Wilcoxon rank-sum and Fisher's exact tests. A multivariable logistic regression model identified factors independently associated with prolapse.

Controls were 3.7 years younger and had lower parity, but groups were similar in terms of race, height, and BMI. Cases had a larger APA (p < 0.0001), interspinous diameter (ISD) (p = 0.001), anterior-posterior (AP) diameter (p = 0.01), and smaller total obturator internus muscle (OIM) area (p = 0.002). There was no difference in the size of the PPA(p = 0.12). Bivariate logistic regression showed age (p = 0.007), parity (p = 0.009), ISD (p = 0.002), AP diameter (p = 0.02), APA (p < 0.0001), and OIM size (p = 0.01) were significantly associated with prolapse; however, PPA was not (p = 0.12). After adjusting for age, parity, and major levator defect, prolapse was significantly associated with increased anterior pelvic area (p = 0.001).

We confirm that a larger APA and decreasing OIM area are associated with prolapse. The PPA was not significantly associated with prolapse.