Pelvic organ prolapse (POP) causes voiding dysfunction (VD), probably due to bladder outlet obstruction (BOO) and/or detrusor underactivity (DU), although the definitive mechanisms remain to be determined.  VD in POP is usually associated with high-grade cystocele [1].  In the present study, we investigated the associations between VD and pelvic organ mobility (POM) evaluated by dynamic magnetic resonance imaging (dMRI). Our hypothesis was that patients with VD had a more mobile bladder.

We included 118 patients with a mean age of 60.3 years who had POP of stage II or less at rest and stage III or more when straining during dMRI.  The presence or absence of VD was demonstrated by a voiding International Prostate Symptom Score (vIPSS) ≥5 (vIPSS5), maximum flow rate (Qmax) <15 mL/s (Qmax15), and post-void residual urine volume (PVR) >50 mL (PVR50) [2, 3].  POM was measured by dMRI as follows: Using the sagittal images, we measured representative points of the pelvic organs, that is, coordinate positions of the bladder neck (BN), the most dependent position of the bladder after straining (B), uterine cervix (C), and anorectal angle (AR) before (at rest) and during intense straining.  To measure them, we used a sacrococcygeal inferior pubic point line (SCIPP) line as an x-axis with the inferior margin of the pubic symphysis as an origin, and a perpendicular line to the SCIPP line at the origin as a y-axis.  The x and y coordinates of each representative point (e.g., BNx and BNy, respectively) were measured before and during straining.  POM was evaluated by the distance between coordinate positions of the representative points before and during straining in x (e.g., BNxx = BNx during straining – BNx at rest) and y directions (eg., BNyy = BNy during straining – BNy at rest) and the distance derived from the Pythagorean theorem (e.g., BNp = [(BNxx)2 + (BNyy)2]1/2.  In addition, we measured the anterior vaginal wall length (AVWL), posterior urethrovesical angle (PUVA), and angle of the urethral inclination (AUI).  Student’s t-test was used to evaluate the association between the presence or absence of VD and these parameters.  Data are presented as mean (SD), and p<0.05 was considered to be statistically significant.

Means of vIPSS, Qmax, and PVR were 4.00 (3.88), 23.63 (12.53) mL/s, and 31.38 (48.38) mL, respectively.  VD was found in 35.6%, 27.0%, and 22.6% of the patients, according to vIPSS5, Qmax15, and PVR50, respectively.  As shown in Table 1, there was no statistically significant association between vIPSS, Qmax, and PVR.  Among all examined associations between parameters on dMRI and VD, Table 2 shows the associations that had p<0.01.  On vIPSS5, patients with VD had a more ventral position or movement of BN, B, C, and AR, longer iUSL and iCL, and smaller AUI compared with patients without VD.  On Qmax15, patients with VD had a more ventral position of C, less caudal position or movement of AR, longer iCL, larger change in AVWL, and smaller PUVA.  On PVR50, patients with VD had smaller PUVA as well as AUI.

When assessing VD by the three criteria, the parameters derived from dMRI that showed significant differences between the VD and non-VD groups vary across these criteria.  The symptoms seem to be caused by more ventral positions or movement of pelvic organs as well as the elongation of the apical supportive structures.  The uroflow rate reflecting detrusor contraction speed and bladder outlet condition was associated with more bladder distention during straining against less sagging of the pelvic floor, which suggests that the decreased Qmax is implicated in reduced detrusor contraction speed and BOO.  PVR reflecting the degree in detrusor contraction duration as well as bladder outlet condition was associated with the narrower angle around the bladder outlet, which implies that the increased PVR in these patients might be caused by BOO.

Factors other than bladder mobility could be also involved in VD in patients with POP.

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