Natural History of Postobstructive Nephropathy: A Single-Center Retrospective Study

Obstructive nephropathy and molecular pathophysiology of renal interstitial fibrosis

The kidneys play a key role in maintaining total body homeostasis. The complexity of this task is reflected in the unique architecture of the organ. Ureteral obstruction greatly affects renal physiology by altering hemodynamics, changing glomerular filtration and renal metabolism, and inducing architectural malformations of the kidney parenchyma, most importantly renal fibrosis. Persisting pathological changes lead to chronic kidney disease, which currently affects ∼10% of the global population and is one of the major causes of death worldwide. Studies on the consequences of ureteral obstruction date back to the 1800s. Even today, experimental unilateral ureteral obstruction (UUO) remains the standard model for tubulointerstitial fibrosis. However, the model has certain limitations when it comes to studying tubular injury and repair, as well as a limited potential for human translation. Nevertheless, ureteral obstruction has provided the scientific community with a wealth of knowledge on renal (patho)physiology. With the introduction of advanced omics techniques, the classical UUO model has remained relevant to this day and has been instrumental in understanding renal fibrosis at the molecular, genomic, and cellular levels. This review details key concepts and recent advances in the understanding of obstructive nephropathy, highlighting the pathophysiological hallmarks responsible for the functional and architectural changes induced by ureteral obstruction, with a special emphasis on renal fibrosis.

Managing Small Ureteral Stones: A Retrospective Study on Follow-Up, Clinical Outcomes and Cost-Effectiveness of Conservative Management vs. Early Surgery

INTRODUCTION

The management of ureteral calculi has evolved over the past decades with the advent of new surgical and medical treatments. The current guidelines support conservative management as a possible approach for ureteral stones sized = 10 mm.

OBJECTIVES

We purport to follow the natural history of ureteral stones managed conservatively in this retrospective study, and attempt to ascribe an estimated health-care and cost-effectiveness, from presentation to time of being stone-free.

MATERIALS AND METHODS

192 male and female patients with a single ureteral stone sized = 10 mm were included in this study. The clinical and cost-related outcome was analyzed for different stone sizes (0-4, 4-6 and 6-10 mm). The effectiveness of selected follow-up (FU) scans was also analyzed.

RESULTS

Stone size was found to be related to the degree of hydronephrosis and to the likelihood of need for a surgical management. Conservative management was found to be clinically effective, as 88% of the patients did not require surgery for their stone. 96.1% of the patients with a stone 0-4mm managed to expel their ureteral stone. Bigger ureteral stones were found to be more costly. The cost-effectiveness of the single FU scans was found to be related to their efficiency, while the global cost-effectiveness of conservative management vs. early surgery was higher for smaller stones (26.8 vs. 17.32% for stones 0-4 vs. 6-10 mm).

CONCLUSION

Conservative management is clinically effective with a significant cost-benefit, particularly for the subgroup of stones sized 0-4 mm, where a need for FU scans is in dispute.

A murine model of irreversible and reversible unilateral ureteric obstruction

Obstruction of the kidney may affect native or transplanted kidneys and results in kidney injury and scarring. Presented here is a model of obstructive nephropathy induced by unilateral ureteric obstruction (UUO), which can either be irreversible (UUO) or reversible (R-UUO). In the irreversible UUO model, the ureter may be obstructed for variable periods of time in order to induce increasingly severe renal inflammation and interstitial fibrotic scarring. In the reversible R-UUO model the ureter is obstructed to induce hydronephrosis, tubular dilation and inflammation. After a suitable period of time the ureteric obstruction is then surgically reversed by anastomosis of the severed previously obstructed ureter to the bladder in order to allow complete decompression of the kidney and restoration of urinary flow to the bladder. The irreversible UUO model has been used to investigate various aspects of renal inflammation and scarring including the pathogenesis of disease and the testing of potential anti-inflammatory or anti-fibrotic therapies. The more challenging model of R-UUO has been used by some investigators and does offer significant research potential as it allows the study of inflammatory and immune processes and tissue remodeling in an injured and scarred kidney following the removal of the injurious stimulus. As a result, the R-UUO model offers investigators the opportunity to explore the resolution of kidney inflammation together with key aspects of tissue repair. These experimental models are of relevance to human disease as patients often present with obstruction of the renal tract that requires decompression and are commonly left with significant residual kidney impairment that has no current treatment options and may lead to eventual end stage kidney failure.

Obstructive renal injury: from fluid mechanics to molecular cell biology

Urinary tract obstruction is a frequent cause of renal impairment. The physiopathology of obstructive nephropathy has long been viewed as a mere mechanical problem. However, recent advances in cell and systems biology have disclosed a complex physiopathology involving a high number of molecular mediators of injury that lead to cellular processes of apoptotic cell death, cell injury leading to inflammation and resultant fibrosis. Functional studies in animal models of ureteral obstruction using a variety of techniques that include genetically modified animals have disclosed an important role for the renin-angiotensin system, transforming growth factor-β1 (TGF-β1) and other mediators of inflammation in this process. In addition, high throughput techniques such as proteomics and transcriptomics have identified potential biomarkers that may guide clinical decision-making.

Postobstructive regeneration of kidney is derailed when surge in renal stem cells during course of unilateral ureteral obstruction is halted

Unilateral ureteral obstruction (UUO), a model of tubulointerstitial scarring (TIS), has a propensity toward regeneration of renal parenchyma after release of obstruction (RUUO). No information exists on the contribution of stem cells to this process. We performed UUO in FVB/N mice, reversed it after 10 days, and examined kidneys 3 wk after RUUO. UUO resulted in attenuation of renal parenchyma. FACS analysis of endothelial progenitor (EPC), mesenchymal stem (MSC) and hematopoietic stem (HSC) cells obtained from UUO kidneys by collagenase-dispersed single-cell suspension showed significant increase in EPC, MSC, and HSC compared with control. After RUUO cortical parenchyma was nearly restored, and TIS score improved by 3 wk. This reversal process was associated with return of stem cells toward baseline level. When animals were chronically treated with nitric oxide synthase (NOS) inhibitor at a dose that did not induce hypertension but resulted in endothelial dysfunction, TIS scores were not different from control UUO, but EPC number in the kidney decreased significantly; however, parenchymal regeneration in these mice was similar to control. Blockade of CXCR4-mediated engraftment resulted in dramatic worsening of UUO and RUUO. Similar results were obtained in caveolin-1-deficient but not -overexpressing mice, reflecting the fact that activation of CXCR4 occurs in caveolae. The present data show increase in EPC, HSC, and MSC population during UUO and a tendency for these cells to decrease to control level during RUUO. These processes are minimally affected by chronic NOS inhibition. Blockade of CXCR4-stromal cell-derived factor-1 (SDF-1) interaction by AMD3100 or caveolin-1 deficiency significantly reduced the UUO-associated surge in stem cells and prevented parenchymal regeneration after RUUO. We conclude that the surge in stem cell accumulation during UUO is a prerequisite for regeneration of renal parenchyma.

Treatment of large impacted proximal ureteral stones: randomized comparison of percutaneous antegrade ureterolithotripsy versus retrograde ureterolithotripsy

PURPOSE

We compared the safety and efficacy of percutaneous antegrade ureterolithotripsy with retrograde ureterolithotripsy for large impacted proximal ureter stones in a prospective randomized manner.

MATERIALS AND METHODS

A total of 91 patients with large impacted proximal ureteral stones, defined as stones >1 cm in size located between the ureteropelvic junction and the lower border of the fourth lumbar vertebra, were prospectively randomized for antegrade (44) or retrograde (47) ureterolithotripsy. Failure of the procedure (conversion to an open procedure), intraoperative and postoperative morbidity, operative time, hospital stay, stone clearance at discharge home, and follow-up were analyzed in each group.

RESULTS

The main complications were bleeding (2.3%; 1 of 43) for the antegrade procedure and ureteral injury (2.3%; 1 of 44) for the retrograde procedure. Percutaneous antegrade ureterolithotripsy was associated with longer operative times (75.4+/-11.8 v 30.6+/-7.8 minutes; P<0.001), longer hospital stay (6.3+/-0.5 v 2.1+/-0.4 days; P<0.001), and a longer interval to return to normal activities (7.8+/-0.7 v 2.7+/-0.6 days; P<0.001). Nevertheless, the percutaneous antegrade procedure had a higher stone-free rate both at discharge home (95.3% v 79.5%; P=0.027), and 1 month post-procedure (100% v 86.4%; P=0.026).

CONCLUSIONS

Percutaneous antegrade ureterolithotripsy is a valuable treatment modality for impacted proximal ureteral calculi larger than 1 cm, and achieves higher stone-free rates than those of retrograde ureteroscopy with holmium:YAG laser lithotripsy. The drawbacks of the antegrade procedure are longer operative time and hospital stay.

A case of acute kidney injury due to complex, partial, multifocal ureteral strictures

BACKGROUND

An 89-year-old man with a history of prostate cancer who had undergone radical prostatectomy 15 years ago presented with hyperkalemia (serum potassium level 6.9 mmol/l) and kidney failure (serum creatinine level 937 micromol/l [10.6 mg/dl]). Ultrasound scan of his kidneys showed mild bilateral hydronephrosis. Although placement of a bladder catheter led to an initial increase in glomerular filtration rate, the improvement was delayed and incomplete. Subsequently, the patient's glomerular filtration rate decreased acutely. This unusual biphasic course of kidney injury begged explanation.

INVESTIGATIONS

Physical examination, measurements of serum creatinine level and electrolytes, imaging of the urinary tract (ultrasound and CT scans), and nephrostograms.

DIAGNOSIS

Acute kidney injury due to upper (multiple ureteral strictures bilaterally) and lower (urethral) urinary tract obstruction.

MANAGEMENT

Placement of bladder catheter and percutaneous nephrostomy tubes followed by bilateral internal ureteral stents.