Urethral function and failure: A review of current knowledge of urethral closure mechanisms, how they vary, and how they are affected by life events

MR defecography in assessing stress urinary incontinence with or without symptomatic pelvic organ prolapse

PURPOSE

Utilize magnetic resonance defecography (MRD) to analyze the primary pelvic floor dysfunctions in patients with stress urinary incontinence (SUI) associated with pelvic organ prolapse (POP), and in SUI patients with asymptomatic POP.

METHOD

We performed MRD in both SUI and POP subjects. As a primary analysis, the functional MR parameters were compared between the isolated POP and POP combined SUI groups. As a secondary analysis, the functional MR data were compared between the POP combined SUI and the SUI with asymptomatic POP (isolated SUI) groups.

RESULTS

MRD noted the main characteristics of SUI combined moderate or severe POP, including the shorter closed urethra length (1.87 cm vs. 2.50 cm, p < 0.001), more prevalent urethral hypermobility (112.31° vs. 85.67°, p = 0.003), bladder neck funneling (48.28% vs. 20.51%, p = 0.020), lower position of vesicourethral junction (2.11 cm vs. 1.67 cm, p = 0.030), and more severe prolapse of the posterior bladder wall (6.26 cm vs. 4.35 cm, p = 0.008). The isolated SUI patients showed the shortest length of the closed urethra (1.56 cm vs. 1.87 cm, p = 0.029), a larger vesicourethral angle (153.80° vs. 107.58°, p < 0.001), the more positive bladder funneling (84.85% vs. 48.28%, p = 0.002) and a special urethral opening sign (45.45% vs. 3.45%, p < 0.001).

CONCLUSIONS

Patients with SUI accompanying POP primarily exhibit excessive urethral mobility and a shortened urethral closure. SUI patients with asymptomatic POP mainly show dysfunction of the urethra and bladder neck, characterized by the opening of the urethra and bladder neck and a shortened urethral closure.

An Overview of the Effect of Aging on the Female Urethra

Urethral function declines by roughly 15% per decade and profoundly contributes to the pathogenesis of urinary incontinence. Individuals with poor urethral function are more likely to fail surgical management for stress incontinence that focus on improving urethral support. The reduced number of intramuscular nerves and the morphologic changes in muscle and connective tissue collectively impact urethral function as women age. Imaging technologies like MRI and ultrasound have advanced our understanding of these changes. However, substantial knowledge gaps remain. Addressing these gaps can be crucial for developing better prevention and treatment strategies, ultimately enhancing the quality of life for aging women.

Evaluation of pelvic structural abnormalities in primiparous women with stress urinary incontinence

INTRODUCTION AND HYPOTHESIS

The objective was to evaluate the morphological characteristics of pelvic floor structure specific to de novo stress urinary incontinence (SUI) in primiparous women using three-dimensional (3D) reconstruction fusion technology based on static MRI combined with dynamic MRI.

METHODS

Eighty-one primiparous women after the first vaginal delivery were studied, 40 with SUI and 41 without SUI. 3D reconstruction models based on static MRI were used to describe the anatomical abnormalities of pelvic floor tissues. Dynamic MRI was used to describe segmental activities of the urethra and vagina. The relationship between the morphometry and postpartum SUI was evaluated by logistic regression analysis and receiver operator characteristic curve.

RESULTS

The differences in the distance from the bladder neck to the pubic symphysis (BSD), the angle between the posterior wall of the urethra and the anterior wall of the vagina, the width of the distal region of the vagina, urethral length, urethral compression muscle volume (CUV), and pubovisceral muscle volume, puborectal muscle volume, were measured, and except for the extremity of the anterior urethral wall, the total displacements (TDs) of the other sites between the two groups were statistically significant (p < 0.05). Logistic regression analysis showed that the BSD decreased, the CUV decreased, the TDs of the first site and the eighth site increment correlated significantly with postpartum SUI occurrence (p < 0.05).

CONCLUSIONS

3D reconstruction fusion technology provides an important support for a precise assessment of the pelvic floor dysfunction. The BSD, CUV, and iliococcygeus muscle volume have certain values in predicting de novo SUI after first vaginal birth.

The Role of the Supine Empty Stress Test in the Evaluation of Women with Stress Urinary Incontinence: A Retrospective Cohort Study

The International Continence Society recommends the supine empty stress test (SEST) as an accessory test in the evaluation of women with urinary incontinence, especially for the presence of intrinsic sphincter deficiency (ISD). The aim of this study was to investigate the relationship between the SEST and clinical findings in women diagnosed with stress urinary incontinence with single voiding cycle ambulatory urodynamics (AUM). AUM tracings of patients with lower urinary tract symptoms (LUTS = Lower urinary tract symptoms) (n = 513) were retrospectively reviewed, and 364 charts with urodynamic SUI were analyzed. Demographics, examination findings, scores of the Sandvik Incontinence Severity Index and validated questionnaires, and AUM findings were compared between SEST-positive and -negative groups. Additionally, the diagnostic accuracy of the SEST in the diagnosis of low abdominal leak point pressure (ALPP ≤ 60 cm H2O) in women with pure urodynamic SUI was calculated. The SEST was positive in 41.8% (n = 152) of the cohort. Women with a positive SEST had higher scores on the Sandvik severity index (9.2 ± 3.6 vs. 7.5 ± 3.8, p = 0.003) and lower ALPP (79.6 ± 29.3 vs. 98.4 ± 31.3, p < 0.001). The negative predictive value of the SEST for ISD was found to be 92.4%. Thus, the SEST seems to be an objective clinical test reflecting urinary incontinence severity while excluding the presence of ISD.

Dysfunction of the aging female mouse urethra is associated with striated muscle loss and increased fibrosis: an initial report

The decline of urethral function with advancing age plays a major role in urinary incontinence in women, impairing quality of life and economically burdening the health care system. However, none of the current urinary incontinence treatments address the declining urethral function with aging, and the mechanisms by which aging impacts urethra physiology remain little known or explored. Here, we have compared functional, morphometric, and global gene expression of urethral tissues between young and old female mice. Bladder leak point pressure (LPP) measurement showed that the aged female mice had 26.55% lower LPP compared to younger mice. Vectorized Scale-Invariant Pattern Recognition (VIPR) analysis of the relative abundance of different tissue components revealed that the mid-urethra of old female mice contains less striated muscle, more extracellular matrix/fibrosis, and diminished elastin fibers ratio compared to young mice. Gene expression profiling analysis (bulk RNA-seq of the whole urethra) showed more down-regulated genes in aged than young mice. Immune response and muscle-related (striated and smooth) pathways were predominantly enriched. In contrast, keratinization, skin development, and cell differentiation pathways were significantly downregulated in aged urethral tissues compared to those from young female mice. These results suggest that molecular pathways (i.e., ACVR1/FST signaling and CTGF/TGF-β signaling) leading to a decreased striated muscle mass and an increase in fibrous extracellular matrix in the process of aging deserve further investigation for their roles in the declined urethral function.

Correlation between the female pelvic floor biomechanical parameters and the severity of stress urinary incontinence

BACKGROUND

Stress urinary incontinence (SUI) is a common condition that requires proper evaluation to select a personalized therapy. Vaginal Tactile Imaging (VTI) is a novel method to assess the biomechanical parameters of the pelvic floor.

METHODS

Women with SUI were enrolled in this cross-sectional study. Participants completed the Medical, Epidemiologic, and Social Aspects of Aging (MESA) questionnaire and the Patient Global Impression of Severity Question (PGI-S) and underwent a VTI examination. Based on the MESA and PGI-S questionnaires, participants were divided into mild, moderate, and severe SUI groups. Fifty-two biomechanical parameters of the pelvic floor were measured by VTI and compared between the groups (mild vs. moderate and severe). SUI Score and Index were calculated from the MESA questionnaire. Pearson correlation was used to determine the strength of association between selected VTI parameters and the MESA SUI Index and MESA SUI Score.

RESULTS

Thirty-one women were enrolled into the study. Significant differences were observed in the VTI parameters 16, 22-24, 38, 39 when the difference between mild and severe subgroups of SUI based on the PGI-S score was examined. Parameter 16 refers to the maximum gradient at the perineal body, parameter 22-24 refers to the pressure response of the tissues behind the vaginal walls, and parameter 38, 39 refers the maximum pressure change and value on the right side at voluntary muscle contraction. VTI parameter 49, describing the displacement of the maximum pressure peak in the anterior compartment, showed a significant difference between the mild SUI and the moderate-severe SUI according to the MESA SUI score (mean ± SD 14.06 ± 5.16 vs. 7.54 ± 7.46, P = 0.04). The MESA SUI Index and SUI Score displayed a positive correlation concerning VTI parameters 4 (the maximum value of the posterior gradient) and 27 (the displacement of the maximum pressure peak in the anterior compartment) (VTI4 vs. MESA SUI Index r = 0.373, P = 0.039; VTI4 vs. MESA SUI Score r = 0.376, P = 0.037; VTI27 vs. MESA SUI Index r = 0.366, P = 0.043; VTI27 vs. MESA SUI Score r = 0.363, P = 0.044).

CONCLUSIONS

Female pelvic floor biomechanical parameters, as measured by VTI, correlate significantly with the severity of SUI and may help guide therapeutic decisions.

Blastopore gating mechanism to regulate extracellular fluid excretion

Fluid uptake and efflux play roles in early embryogenesis as well as in adult homeostasis. Multicellular organisms have two main pathways for fluid movement: cellular-level, such as transcellular and paracellular pathways, and tissue-level, involving muscle contraction. Interestingly, early Xenopus embryos with immature functional muscles excrete archenteron fluid via a tissue-level mechanism that opens the blastopore through a gating mechanism that is unclear. Using microelectrodes, we show that the archenteron has a constant fluid pressure and as development progress the blastopore pressure resistance decreases. Combining physical perturbations and imaging analyses, we found that the pushing force exerted by the circumblastoporal collars (CBCs) at the slit periphery regulates pressure resistance. We show that apical constriction at the blastopore dorsoventral ends contributes to this pushing force, and relaxation of ventral constriction causes fluid excretion. These results indicate that actomyosin contraction mediates temporal control of tissue-level blastopore opening and fluid excretion in early Xenopus embryos.

Stress urinary incontinence is caused predominantly by urethral support failure

Whales are mammals that can dive to depths of > 1000 m without the high water pressure pushing open their mouth or anus. The same is true for the female urethra. The meatus externus and internus are seals that cannot be pushed open by high water pressures. Recent evidence suggests that the female meatus internus is pushed open when the bladder pressure exceeds the urethral pressure. For a relaxed detrusor, this opening is not possible for at least three reasons: the law of elastic collision, Pascal’s law of hydrostatics and the Hagen-Poiseuille law. The three laws do not support that urethral function failure is the predominant cause of stress urinary incontinence (SUI); however, they do support that urethral support failure is. Influential urogynecologists claim the opposite. TVT surgery, according to the integral theory of SUI (IT), has high failure rates because it does not principally prevent the urethra from hanging on a less mobile bladder neck. In the case of a long urethra, the tape is set too distally, and in hypomobile SUI, the use of a tension-free suburethral tape is unwarranted/ineffective, because the proximal urethra is not elevated above its resting position. A successful operation corrects urethral support failure and not urethral function failure.