40: Pelvic cross sectional area at the level of the levator ani is associated with prolapse

Pressure is transferred to the pelvic floor through an aperture bordered by the pubic bone anteriorly, sacrum, sacrospinous ligaments and coccygeus muscles posteriorly, and obturator internus muscles (OIM) laterally (Figure 1a-c). A prior small study showed that the anterior portion of this plane is larger in prolapse. This study aims to assess the relationship between prolapse and both anterior (APA) and posterior pelvic area (PPA) in a larger, more diverse population. Pelvic MRIs from 96 women (66 without prolapse, 30 with prolapse) were included in this case-control study. Using 3D Slicer software, the measurement plane was tilted to include the ischial spines and the inferior pubic point, approximating the level of the levator ani attachments (Figure 1b, c). The borders of the measurements can be seen in Figure 1c. Three raters made all measurements and interrater reliability was assessed. Demographic characteristics were compared across groups using Wilcoxon Rank and Fisher’s exact tests. A multivariate logistic regression model was developed to identify factors independently associated with prolapse. Women without prolapse were an average of 3.7 years younger than cases and had lower parity but groups were similar in terms of race, height, and BMI. Patients with prolapse had a significantly larger interspinous distance (ISD), anterior-posterior (AP) diameter, APA, and smaller OIM area (Figure 2). There was no difference in PPA. Bivariate regression showed that age, parity, ISD, AP diameter, APA and OIM size were significantly associated with prolapse (Table). PPA was not significantly associated with prolapse (OR 1.06, P=0.12). After adjusting for age, race, parity, ISD and AP distance, prolapse was significantly associated with increased APA (OR 1.19, p=0.01), while larger OIM area had decreased odds of prolapse (OR 0.76, p=0.03). Intraclass correlation coefficient was 0.92 indicating good interrater reliability. In a larger, more diverse group of women we confirm that APA is larger in prolapse, allowing for greater force transference to the pelvic floor. Decreasing OIM area is also associated with prolapse, possibly due to sarcopenia. The posterior measurements of this plane were not significantly associated with prolapse.View Large Image Figure ViewerDownload Hi-res image Download (PPT)View Large Image Figure ViewerDownload Hi-res image Download (PPT)