An interesting prospective study in patients to determine the relationship between metabolic urine conditions and the formation, severity, and composition of encrustations in ureteral stents in ninety stone-formers patients.

All patients were required to collect a 24 hours metabolic urine sample while the ureteral stent was in place. The studied parameters were pH, diuresis, urine concentration, and urine total amounts of creatinine, urate, calcium, phosphate, magnesium, oxalate, and citrate. To avoid any bias, the researchers used the same kind of ureteral stent in all patients enrolled in the study, namely a soft-polyurethane compound ureteral stent without any coating to inhibit biofilm formation. Stereoscopic and electron microscopy were performed to identify the type of ureteral stents embedded deposits (calcium oxalate, uric acid, and infectious and non-infectious phosphates).

The results of the study show that 70% of stents were encrusted; and, 42% had a moderate degree of encrustation. The median indwelling time was 58 days. The most common encrustation type was calcium oxalate, but infectious phosphates were predominant in the high-encrustation group. Greater calciuria, uricosuria, indwelling time, and decreased diuresis were observed in stents with a higher degree of encrustation. When authors compared to non-encrusted stents, patients with calcium-oxalate-encrusted stent showed greater calciuria, phosphaturia, indwelling time, and reduced diuresis; patients with uric-acid-encrusted stent showed greater uricosuria; and patients with infectious and non-infectious phosphate encrustation showed greater urinary pH with statististical significance.

Authors showed a high concordance between encrustation and stone compositions, reaching almost 86%, supporting the theory that the lithogenic factors involved in stone and encrustation formation could be the same. This is the first study to directly research the role of metabolic urinary conditions in the formation, severity, and type of encrustation present on standard ureteral stents.

The results suggest a new role for 24 hours urine metabolic analysis, as it could be very useful in identifying patients at a high risk of encrustation, allowing for targeted and personalized treatment, thus reducing subsequent complications and improving patients’ quality of life. On the one hand, by reducing stenting duration or by using prophylactic measures, such as oral inhibitors of crystallisation.

This type of study clearly shows the close relationship between lithiasis and encrustation in this group of stone-formers patients, which allows early action to be taken, especially in those patients who are expected to undergo ureteral stenting for a long period of time. In these patients, the use of crystallisation inhibitors (Canoxidin®), which have been shown to be effective in reducing the rate of encrustation, is an effective preventive therapy.

The present study is a systematic review with meta-analysis comparing conventional stents and new stent designs known as "intraureteral" stents. Unfortunately, current double-joint ureteral stents are associated with a decrease in patients' quality of life of up to 70%. This is mainly related to the design of current ureteral stents, firstly because they cause vesicoureteral reflux increasing of intrapelvic pressure and secondly because of the discomfort caused by ureteral stent distal end at the trigone of the bladder which is a very sensitive area with nerve connections for the control of bladder function and continence. In this regard, many efforts have been made to improve stent design to avoid these two sources of stent-associated effects.

The inclusion criteria were: 1) patients >18 years old; 2) patients who need ureteral stent placement, including patients after ureteroscopy or preparing stenting for secondary ureteroscopy; 3) randomized clinical trials. The literature search was updated to February of 2023. After screening 321 literatures, six prospective randomized clinical trials were included in this systematic review and meta-analysis, with 557 patients.

Compared to conventional ureteral stents, intraureteral stents had beneficial effects to reduce stent-related symptoms in middle (one week) and late stages (two weeks). Intraureteral stent caused less urinary symptoms and body pain in mid-to-late stages of stent implantation. In addition, intraureteral stent also showed better outcomes in postoperative emergency visit and readmission.

However, there is no significant difference between intraureteral stent and conventional stent in the early stage (< 1 week) of stent implantation and long-term (4 weeks) after stent removal.

This systematic review and meta-analysis reveal that regardless of the stage of treatment (early-stage outcomes, middle stage outcomes, late-stage outcomes, and long-term evaluation), the efficacy and safety of intraureteral stent are no worse than that of conventional stent. Intraureteral stents can be employed as alternative methods to conventional ureteral stent to increase the quality of life of patients.

In this study, authors assess their own database for patients with the Resonance stent for benign obstructive disease, its efficacy in preserving renal function, its long-term durability and a cost analysis of placing the RS versus a polymeric stent.

Primarily utilized in patients with inoperable malignant-ureteral-obstruction, the Resonance stent is a cobalt-chromium-nickel-molybdenum alloy-based Double-J ureteral stent. The stent is relatively resistant to encrustation, epithelial tissue ingrowth and extrinsic compression, allowing for a recommended indwell time of 12 months. The Resonance stent provides safe and sufficient management of malignant extrinsic ureteral obstruction, but its use in benign disease does not yet show a high level of evidence in the scientific literature.

43 patients were enrolled in this retrospective study, 74% of them did not require any removal or replacement of the stent within 6 months after placement and 26% patients with premature failure (64% developed an UTI) of the stent requiring either replacement or removal of the Resonance stent within 6 months of the initial placement. The mean indwell time was 9.7 months: patients underwent a stent exchange an average of 1.1 times per year. At the time of stent replacement/removal, 21% patients had encrustation. Among the encrusted stents patients, 9% required laser lithotripsy for their removal. The authors highlight in their study that although the initial cost of placing a single metallic stent exceeds the cost of a polymeric stent, the advantage of a longer indwell time with fewer necessary stent exchanges favors the use of Resonance for managing benign obstructive disease.

Resonance stent deployment in patients with a benign ureteral obstruction proved to be a cost-effective means for preservation of renal function and maintenance of parenchymal volume.