Position and orientation of vaginal pessaries in situ on magnetic resonance imaging.

introduction and hypothesisWe hypothesize that there are differences in the position and orientation of ring and Gellhorn pessaries in situ on magnetic resonance imaging (MRI).

methodsThis was a retrospective cohort study comparing MRI findings in 25 women with pessaries in situ at the time of imaging. Scanner coordinates for anatomic and pessary landmarks were obtained and transformed to 3D Pelvic Inclination Correction System coordinates using MATLAB software. The normal vector to the pessary disc was computed and compared to the positive y-axis in the sagittal and coronal planes to determine XY and YZ disc angles, respectively. Comparisons between groups were made using Wilcoxon rank, Fisher's exact, and Brown-Forsythe tests.

resultsTwenty-one women with ring pessaries and four women with Gellhorn pessaries met inclusion criteria for the study. Women with ring pessaries were younger (68.4 vs. 80.7 years, p = 0.003) but had similar BMI, vaginal parity, history of hysterectomy, and anatomic characteristics. Ring pessaries had a smaller diameter (59.5 vs. 79.3 mm, p = 0.004) and were positioned further posterior with respect to the inferior pubic point (midpoint X position 42.6 vs. 29.5 mm, p = 0.004). There were significant differences in the magnitude and variance of the XY disc angle (57.0 ± 14.0 vs. -1.2 ± 2.8 degrees, p = 0.002 for magnitude, p = 0.012 for variance) but not the YZ disc angle (3.3 ± 30.6 vs. 1.5 ± 7.7 degrees, p > 0.05 for both) between groups.

conclusionsWe found differences in the position and orientation between ring and Gellhorn pessaries in situ using an anatomic 3D reference system. These findings provide insight into the mechanism of action of vaginal pessaries.