Differences in Pelvic Muscular Shape and Thickness in Women With and Without Significant Bladder Descent.

Introduction and hypothesis: Pelvic organ prolapse (POP) is the descent of pelvic organs, causing patient discomfort. Despite its increasing prevalence, agreement in the field as to the cause is elusive. Weakness in pelvic floor muscles is implicated, but specific structural changes remain unclear. This study aimed to identify such differences in the levator ani, hypothesizing differences in pelvic muscle shape between greater and lesser bladder descent.

Methods: We reviewed our patient database for cystocele diagnoses via MR defecography, including patients with static axial MRIs and dynamic midsagittal defecography. Patients were divided into two groups based on bladder descent relative to the genital hiatus (a measure our group had previously used). We used a statistical shape model of levator shapes to compare the groups. Additionally, we conducted MRI-based measurements (thickness of the obturator internus and anterior pelvic area) which have previously shown differences in similar groups.

Results: Among 67 cystocele patients, 28 had greater bladder descent. The shape model identified significant variation in pelvic floor shape, specifically near the arcus tendineus levator ani (ATLA). The MRI-based measurements showed an increase in anterior pelvic area (53.8 ± 6.0 vs. 58.0 ± 5.3 cm², p < 0.001) with increased prolapse severity and thinning of obturator's along the ATLA (16.2 ± 2.7 vs. 13.9 ± 2.2 mm, p < 0.001), specifically in the region around the insertion of the levators and obturators.

Conclusions: Patients with greater bladder descent exhibited a larger anterior pelvic area, thinner obturators, and greater pelvic floor muscle descent, potentially due to muscle detachment at DeLancey's level II support.