The valve bladder: etiology and outcome

A grading system for evaluation of bladder trabeculation

PURPOSE

To establish a parameter-based grading system for evaluating bladder trabeculation (BT).

MATERIALS AND METHODS

A retrospective analysis was conducted on children diagnosed with posterior urethral valve (PUV) or neurogenic bladder (NB) who underwent voiding cystourethrogram (VCUG), urodynamic testing, and urological ultrasonography between January 2016 and October 2022. Cases involving urologic surgery, secondary bladder pathology, and an interval of more than 12 months between examinations were excluded. A parameter named Bladder Dispersion (BD) was calculated through fluoroscopic images, and the grading system was developed as follows: BD < 40 (Grade 0), 40 ≤ BD < 60 (Grade 1), 60 ≤ BD < 90 (Grade 2), BD ≥ 90 (Grade 3). Grades 0-1 were classified as low-risk group, while grades 2-3 were classified as high-risk group. Analysis of variance, Kruskal-Wallis test, and Chi-square test were performed to compare urodynamic results and complications across different grades and groups.

RESULTS

A total of 74 patients were eligible to participate, which included 46 boys (62.2%) and 28 girls (37.8%), the mean age was 75.18 ± 48.39 months. Among them, 11 (14.9%) were PUV, 50 (67.6%) were NB, and 13 (17.5%) were PUV and NB. Significant differences were observed in maximum detrusor pressure, post-void residual urine ratio, and compliance among grades 0-3. Severe hydronephrosis and histories of urinary tract infection were more prevalent in the high-risk group.

CONCLUSION

A reliable grading system with objective standards was proposed which could aid in the assessment of BT severity.

Bladder height width ratio on voiding cystourethrogram as a predictor of future valve bladder in children with posterior urethral valve

BACKGROUND/AIMS

Prompt and early treatment of valve bladder is known to improve renal outcome in patients with PUV. We hypothesized that bladder height width ratio (HWR) measurement on voiding cystourethrogram (VCUG) could predict development of valve bladder.

METHODS

All patients who underwent primary PUV ablation and evaluated later with urodynamics were included. Valve bladder was suspected when there were daytime wetting, persistent hydroureteronephrosis, and elevated detrusor pressures on urodynamics. VCUGs were analysed for HWR: maximum height/width of bladder. ROC curve analysis was performed to identify HWR that could predict development of urodynamic abnormality.

RESULTS

Between 2012 and 2017, 102 patients were studied: median age at valve ablation 25 days (3-125 days); follow-up 5 years (3-7 years). The ROC curve comparing post-ablation HWR with occurrence of valve bladder showed a cut-off of 1.45 (AUC 0.93). HWR cut-off of 1.45 had a sensitivity of 89% and specificity of 84% in predicting future valve bladder. Detrusor overactivity was noticed on urodynamics in 41/55 (74%) of those with HWR > 1.45 compared 5/47 (11%) in those with HWR < 1.45 (p = 0.001).

CONCLUSION

Bladder height width ratio on VCUG is a useful parameter to predict development of future valve bladder in children with PUV.

Safety and short-term efficacy of mirabegron in children with valve bladder: a pilot study

AIMS

This pilot study aims to assess the short-term efficacy and safety of mirabegron in valve bladder, an important cause of persistent hydronephrosis after successful treatment of posterior urethral valves (PUV).

METHODS

Twenty-two patients with early valve bladder (no residual PUV; persistent hydronephrosis, wetting and urodynamic evidence of detrusor overactivity) were included. Three subjective parameters: frequency, wetting episodes; patient perception of bladder condition score (PPBC) and four objective parameters: uroflow index (UI = Qave/Qmax), voided volume (VV = voided volume/ expected bladder capacity), maximum filling pressure (P det-max) and society of fetal urology (SFU) hydronephrosis grading were analysed pre- and post-3-month treatment with mirabegron (0.5-1 mg/kg/day). All patients were observed for heart rate, BP, ECG changes during therapy.

RESULTS

There was significant reduction (p = 0.001) in mean frequency (pre 15; post 10), wetting episodes (pre 5; post 2) and PPBC (pre 4; post 3). There was significant improvement (p = 0.01) in mean UI (pre 0.3; post 0.5), VV (pre 0.54; post 0.72), Pdet-max (pre 42; post 25) and hydronephrosis grade (pre 3.5; post 2.2). There were no significant side effects.

CONCLUSION

This pilot study establishes short-term efficacy and safety of mirabegron in valve bladder with overactivity. Further larger long-term studies are warranted.

Development and validation of a bladder trabeculation grading system in pediatric neurogenic bladder

Bladder trabeculation (BT) is commonly noted on cystogram images of patients with neurogenic bladder (NB). BT is associated with a hostile bladder often requiring prompt, more aggressive management. We aimed to define and validate a reliable grading system for BT severity. The proposed grading system will improve clinicians and radiologist's communication and serve as a foundation for future studies in the field of NB. The study was conducted in two phases: 1) Development of a grading system for BT and 2) testing of the proposed grading system for reliability and validity. Agreement between raters was assessed using Cohen's Kappa. Inter-rater reliability and intra-rater reliability was assessed using intra-class correlation coefficients (ICC) and Spearman's p (rho) correlation coefficient. The content of the grading system was assessed for face validity by senior pediatric urology and radiology experts. We observed inter-rater reliability with ICC of 0.998 (95%CI 0.996-0.999, p < 0.001), and a Cohen's Kappa ranging from 0.795 to 1.0, p < 0.001 and Spearman's p (rho) correlation coefficient ranging from 0.910 to 1.0, p < 0.001 between raters on the decided grades of BT. In conclusion, we established a defined grading system for BT severity that has substantial inter/intra-rater reliability and validity. This grading system could be useful for improving clinician and radiologist's communication about the status of a child's bladder wall and serve as a foundation for future studies assessing severity of NB.

The Murine Bladder Supports a Population of Stromal Sca-1+/CD34+/lin- Mesenchymal Stem Cells

Bladder fibrosis is an undesired end point of injury of obstruction and often renders the smooth muscle layer noncompliant. In many cases, the long-term effect of bladder fibrosis is renal failure. Despite our understanding of the progression of this disease, little is known about the cellular mechanisms that lead to a remodeled bladder wall. Resident stem (progenitor) cells have been identified in various organs such as the brain, heart and lung. These cells function normally during organ homeostasis, but become dysregulated after organ injury. Here, we aimed to characterize a mesenchymal progenitor cell population as a first step in understanding its role in bladder fibrosis. Using fluorescence activated cell sorting (FACS), we identified a Sca-1⁺/ CD34⁺/ lin^- (PECAM^-: CD45^-: Ter119^-) population in the adult murine bladder. These cells were localized to the stromal layer of the adult bladder and appeared by postnatal day 1. Cultured Sca-1⁺/ CD34⁺/ lin^- bladder cells self-renewed, formed colonies and spontaneously differentiated into cells expressing smooth muscle genes. These cells differentiated into other mesenchymal lineages (chondrocytes, adipocytes and osteocytes) upon culture in induction medium. Both acute and partial obstruction of the bladder reduced expression of CD34 and changed localization of Sca-1 to the urothelium. Partial obstruction resulted in upregulation of fibrosis genes within the Sca-1⁺/CD34⁺/lin^- population. Our data indicate a resident, mesenchymal stem cell population in the bladder that is altered by bladder obstruction. These findings provide new information about the cellular changes in the bladder that may be associated with bladder fibrosis.

The molecular pathways behind bladder stretch injury

Stretch injury is a non-reversible process that changes the cellular and extracellular characteristics of the bladder wall, leading to bladder dysfunction. Posterior urethral valve and neurogenic bladder are examples of disorders that may lead to stretch injury. There is a lack of understanding of the molecular processes leading to stretch injury. The current literature is reviewed in this paper, with the aim of giving some insight into the molecular and genetic pathways of bladder stretch injury.

Mechanotransduction of extracellular signal-regulated kinases 1 and 2 mitogen-activated protein kinase activity in smooth muscle is dependent on the extracellular matrix and regulated by matrix metalloproteinases

Excessive wall stretch of distensible hollow organs in cardiovascular and urinary systems can activate matrix metalloproteinases (MMPs), thereby releasing matrix neoepitopes and growth factor ligands, leading to ERK1/2 activation. However, the role of MMPs in mechanotransduction of ERK1/2 signaling in the bladder is unknown. We examined bladders undergoing sustained distension over time, which provides a novel platform for smooth muscle mechanotransduction studies. Bladder distension ex vivo caused increased proliferation and MMP activity. Conditioned medium from distended compared with undistended bladders induced proliferation in bladder smooth muscle cells (BSMCs). When conditioned medium from distended bladders was used to proteolyze collagen type I matrices, matrices augmented BSMC proliferation, which was inhibited if bladders were distended in presence of broad-spectrum MMP inhibitors. Distension of ex vivo bladders also induced ERK1/2 phosphorylation in situ, which was dependent on MMP activity in the intact bladder. Similarly, stretching BSMCs in vitro induced increases in ERK1/2 activation and ERK1/2-dependent proliferation under discrete mechanical conditions, and distension conditioned medium itself induced MMP-dependent ERK1/2 activation in BSMCs. Overall, stretch-induced proliferation and ERK1/2 signaling in bladder tissue and BSMCs likely depend on secreted MMP activity. Identification of intermediaries between MMPs and ERK1/2 may elaborate novel mechanisms underlying mechanotransduction in bladder smooth muscle.

Role of signal transducer and activator of transcription 3 (STAT3) in stretch injury to bladder smooth muscle cells

Excessive stretch of the bladder can lead to wall thickening including the growth of bladder smooth muscle cells (BSMC). Only three phospho-proteins (JNK, p38, and PI3K) have been previously shown to participate in stretch-induced BSMC growth. CD1 mouse bladders were hyper- or non-distended by our ex vivo bladder distention model and screened, by a commercial screening method, for phosphorylated signaling proteins. This uncovered a factor previously unexamined for its role in bladder stretch injury: signal transducer and activator of transcription 3 (STAT3). STAT3 was assessed for its role in mitogen- and stretch-induced BSMC proliferation. Proliferation was assessed by 3H-thymidine incorporation/cell counting in response to mitogenic stimulation or to stretch on silastic collagen or carboxyl-coated membranes. JAK2, upstream of STAT3, was inhibited by AG490 (2 microM). Ex vivo distention of bladders activated a discrete number of kinases, including two MAPK pathways (JNK and ERK2) and STAT3. STAT3 signaling was activated during hyperdistention of intact bladder and by stretch and mitogenic treatments of BSMC in vitro. JAK2/STAT3 inhibition by AG490 blocked mitogen- and stretch-induced BSMC proliferation. Thus, BSMC stretch responses may involve the recruitment of both growth factor and mechanically induced BSMC growth responses integrated by a common signaling pathway, STAT3.

Renal transplantation in children with posterior urethral valves

The objective of this study was to analyze whether renal transplantation (RT) in children with posterior urethral valves (PUV) constitutes a special group with respect to groups with different etiologies of end-stage renal disease (ESRD). Between 1979 and 2004, 22 RT were performed in 19 children with PUV. The median age at RT was 10 years (range: 1.3-17). Immunosuppression was provided by triple therapy and polyclonal/monoclonal antibodies. This group was compared with the two control groups: (1) glomerulopathy (n=62) and (2) pyelonephritis/dysplasia (n=42) without lower urinary tract disease, transplanted in the same period. Ten graft losses occurred in 22 transplants: thrombosis (2), acute rejection (3), chronic graft nephropathy (2), and death of patients (3) with a functioning graft in the 1st postoperative month. We did not find significant differences versus the control group in renal function or probability of graft or patient survival at 1, 5, and 10 years. We observed a greater risk of urological complication in patients with PUV. RT with PUV constitutes a special group due to the compulsory young age and the need for careful and complex medicosurgical management; nevertheless, the results achieved were similar to those obtained in our general RT population.