Genital descent occurs along gravity and is subject to ageing or birth-related injuries of organ-supporting pelvic floor structures. Injuries of the levator ani muscle (LAM) have a high impact on later pelvic organ disorders. In premenopausal women a reduced function of the pelvic floor was directly correlated with defects in the LAM. However, a factor that has not yet been fully elucidated is the organ-specific weight that acts on the pelvic floor. Elevated organ specific weight of female pelvic organs in premenopausal women is mostly due to pregnancies or fibroids. Uterine fibroids are a common reason for increased uterine volume and are found in up to over 80% of women below the age of 50.
Aim of this MR-imaging study is to assess the impact of uterine volume in premenopausal, nulliparous women with and without uterine fibroids on the organ location of the three pelvic compartments.

The study was performed in a cohort study of 2615 MR-scans of the female pelvis in the period of 01.01.2006-31.12.2017. Exclusion criteria were other tumors than uterine fibroids, age <18 or >40 years, endometriosis, MRI slice thickness <7mm, pelvic deformation or POP. The position of the three pelvic compartments, namely the internal urethral meatus or bladder neck for the anterior, the cervix for the apical, and anorectal point for the posterior compartment were measured in the 3D PICS coordinate system where per definition point 0/0/0 is the inferior pubic point. The 3D-PICS is a right-handed coordinate system where the y-axis points along the body axis. Negative y-values are cranially of the 3D PICS plane. X-values point along the anterio-posterior axis and the positive z-axis points towards the right side. The uterine volume in women with and without fibroids was calculated with the Myrian Imaging Layer Software.

108 women met the inclusion criteria: 51 women with fibroids (mean age 34.4 years, median volume 424.0cm3) and 57 women without (27.8 years, 59.3cm3) (both p<0.001). In the fibroid group the cervical point was significantly lower above the PICS plane than in the control group (mean y-value -38.6mm vs. -51.1mm, p<0.001). The same was true for the position of the anterior (-13.7mm vs. -26.0mm, p<0.001) and the posterior compartment (-16.4mm vs. -9.7mm, p<0.001). In the high-volume fibroid group (>500 cm3) descent did not differ significantly anymore (-48.2mm vs. -51.1mm, p=0.385).

Our research is the first to compare uterine volume with the position of the three pelvic compartments known to be involved in genital descent measured in a 3D coordinate system (3D PICS).

Genital descent differed significantly if uterine fibroids are present and if the uterine volume with fibroids is between 100 and 500cm3. At a volume >500cm3 the uterine fibroids seem to prevent the descending of the three compartments. The significant descent at higher age of the patient is explained by the higher prevalence of uterine fibroids in women above 30 years of age.

Continence 2S2 (2022) 100304
DOI: 10.1016/j.cont.2022.100304