Potential strategies to prevent encrustations on urinary stents and catheters - thinking outside the box: a European network of multidisciplinary research to improve urinary stents (ENIUS) initiative

Ureteral stent encrustation: evaluation of available scores as predictors of a complex surgery

BACKGROUND

Stent encrustation is an uncommon event (13%) with a significant impact in patients' management. Aim of our study was to evaluate the available grading systems for encrusted stents.

METHODS

A retrospective analysis of encrusted stents was performed in four Italian centers between 2006 and 2020. Encrusted stents were classified according to four classifications: the Forgotten Encrusted Calcificated (FECal) Score, the Kidney Ureter Bladder (KUB) Score, the Visual Grading for Ureteral Encrusted Stent Classification and the Encrustation Burden Score (EBS). Classifications were evaluated to predict complex surgery defined as: long operative time (>60 min), need of more than one surgery, and need of a percutaneous approach. The scores were compared with receiver operating characteristic (ROC) analysis as predictors of complex surgery.

RESULTS

Seventy-seven patients were evaluated with a median age of 62 years (65/70). Overall FECal score >2 was present in 45/77 (58%) patients, median KUB score was 9 (6/14) and severe EBS was found in 47/77 (63%) patients. Patients were managed with cyst lithotripsy in 13/77 (17%), with ureteroscopy in 58/77 (75%) and with percutaneous nephrolithotomy (PCNL) in 6/77 (8%). Overall, 6/77 (8%) patients required a second intervention to remove the encrusted stent. All classifications predicted the need of complex surgery. On ROC analysis KUB score presented a better accuracy in predicting complex surgery compared to FECal, V-GUES and encrusted burden.

CONCLUSIONS

KUB score, FECal score, V-GUES score, and encrustation burden accurately predict the need of a complex surgery. KUB showed to be superior to other classifications according to our results.

Urinary Stent Development and Evaluation Models: In Vitro, Ex Vivo and In Vivo-A European Network of Multidisciplinary Research to Improve Urinary Stents (ENIUS) Initiative

Background: When trying to modify urinary stents, certain pre-clinical steps have to be followed before clinical evaluation in humans. Usually, the process starts as an in silico assessment. The urinary tract is a highly complex, dynamic and variable environment, which makes a computer simulation closely reflecting physiological conditions extremely challenging. Therefore, the pre-clinical evaluation needs to go through further steps of in vitro, ex vivo and in vivo assessments. Methods and materials: Within the European Network of Multidisciplinary Research to Improve Urinary Stents (ENIUS), the authors summarized and evaluated stent assessment models in silico, in vitro, ex vivo and in vivo. The topic and relevant sub-topics were researched in a systematic literature search in Embase, Scope, Web of Science and PubMed. Clinicaltrials.gov was consulted for ongoing trials. Articles were selected systematically according to guidelines with non-relevant, non-complete, and non-English or Spanish language articles excluded. Results: In the first part of this paper, we critically evaluate in vitro stent assessment models used over the last five decades, outlining briefly their strengths and weaknesses. In the second part, we provide a step-by-step guide on what to consider when setting up an ex vivo model for stent evaluation on the example of a biodegradable stent. Lastly, the third part lists and discusses the pros and cons of available animal models for urinary stent evaluation, this being the final step before human trials. Conclusions: We hope that this overview can provide a practical guide and a critical discussion of the experimental pre-clinical evaluation steps needed, which will help interested readers in choosing the right methodology from the start of a stent evaluation process once an in silico assessment has been completed. Only a transparent multidisciplinary approach using the correct methodology will lead to a successful clinical implementation of any new or modified stent.