#06 Click here to see the previous editions March 09, 2024
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Welcome to STENT News! In this newsletter, we will cover about the most relevant evidence in the use and development of stents, catheters and another indwelling urological devices. Stay tuned for updates and insights on this important topic.

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Dear Stent Fans. Welcome to this issue of Stent News.

In this sixth newsletter on urinary stents there are two reviews and one very interesting clinical study that I hope will be of interest to you. In this newsletter I comment three very different issues related to stents. The first manuscript is a review of a recurrent but very important topic, despite its low incidence rate, because it can become a major therapeutic problem, because its resolution in some cases requires great experience and combined approaches, and because of the enormous healthcare costs associated with forgotten ureteral stents. In the second review paper, we focus on the important effects of increasing age and ureteral stent implantation on urinary tract infections in kidney transplant patients. A very helpful review for clinical application in renal transplantation. Finally, a comparative clinical study on the management of malignant ureteral obstruction and its treatment with polymeric stents or metallic ureteral stents, which also provides very precise information for the management of these patients.

I hope they will be of interest to you.

img Forgotten ureteral stents: a systematic review of literature. BMC Urol. 2024.
Wang X, et al.
img 4'
https://pubmed.ncbi.nlm.nih.gov/38443863/ img

The authors of this recent manuscript show an interesting systematic review associated with an issue that is highly evaluated in literature, forgotten ureteral stents. Unfortunately, often a very complex situation involving the kidney, ureter and bladder, requiring multimodal endoscopic procedures and even invasive surgery that can be performed simultaneously, sequentially or separately. Addressing in this manuscript aspects related to forgotten ureteral stents and especially on the problems and possible solutions of this late complication of ureteral stents.

The first highlight is the number of patients included in the review, 1292. Remarkably, the mean indwelling time was 33.5 months (range from 3 months to 32 years). Regarding the causes of this forgetting, it is worth highlighting the following: patient-related (83.9%), which included poor compliance, lapse in memory, and misconceptions about the necessity of timely removal. This reinforces the earlier manuscripts' statement that patient education is very important, which can be done with very clear explanations or with illustrative leaflets.

The main symptoms reported in these patients are flank pain (37.3%), lower urinary tract symptoms (33.3%), as well as haematuria (22.8%). Regarding the most frequent complications, those expected in these patients are encrustation (80.8%) and UTI infections (40.2%). Common risk factors for stent encrustation are long indwelling time, UTIs, chronic renal failure, recurrent or residual stones, lithogenic history, metabolic abnormalities, congenital renal anomalies and ureteral obstruction, of which indwelling time and history of urolithiasis were major contributing factors.

Unfortunately, the management of these patients is not always easy. There are currently no guidelines, but there are several algorithms in the literature for the management of forgotten stents. Single-session removal is often discouraged, and it is better to stage the procedures to avoid long intraoperative time. With improvements in surgical armamentarium and techniques, removing fractured or encrusted stents in a single endourologic session could be achieved with a reasonable operating time and acceptable morbidity. A strong message of this manuscript is that this type of procedure, due to its complexity and the need for expertise to avoid further complications, should be performed in an experienced centre. Combined endourological procedures can achieve safe treatment.

Although forgotten ureteral stents are uncommon, they are likely to cause troublesome and severe complications. The management should be individualised using different treatment modalities, with their advantages, to minimise patients' morbidities. Patient education on timely stent removal is essential. Registries and monitoring systems should be maintained for easy tracking of stents, especially in patients with poor compliance.

img Effect of increasing age and ureteral stent implantation on urinary tract infections after kidney transplantation - update of recent literature
Omic H, et al.
img 4'
https://pubmed.ncbi.nlm.nih.gov/38426237/ img

The authors show an interesting review on effects of increasing age and ureteral stents on the risk of urinary tract infections in kidney transplant recipients. The importance of UTIs is particularly evident from their high incidence in transplant recipients, representing one of the leading causes for morbidity, hospitalization rates, and even mortality. It is worth keeping in mind that according to the literature, at least one in four kidney transplant recipients will have a UTI in the first year after transplantation.

Age is an important predictor of outcome in transplant patients, as both recipient and donor age can influence transplant success. A recent meta-analysis involving 3364 patients and a UTI incidence of 38% revealed that older age is a weak but significant risk factor for UTI in kidney transplant recipients. Each additional year represents a 3.2% increase in the likelihood of UTI. The risk factor of age remains pivotal, yet the varying study outcomes necessitate a nuanced understanding of its implications.

Although the prophylactic use of ureteral stents is effective in preventing certain post-transplant complications, and their use is recommended by European guidelines, it is also important to note that ureteral stents are not without possible adverse effects. The challenge of determining optimal ureteral stents removal the timing further complicates post-transplant care, with insufficient evidence to guide practices. The existing recommendations, applied to kidney transplant recipients, propose limiting the stenting duration to 4 weeks. In cases of severe UTIs between 2-4 weeks after transplantation, there is a suggestion to consider early stent removal while carefully weighing the risk of urological complications. Additionally, the type of stents played a crucial role, with external stents associated with a 1.69 times higher UTI risk. It is not clear if ureteral stents increase UTI risk in elderly patients more than in the general transplant population.

img Malignant ureteral obstruction: comparison of metallic, 8 French and 6 French ureteric stents after failure of initial ureteric stent. World J Urol. 2024.
Ong K, et al.
img 3'
https://pubmed.ncbi.nlm.nih.gov/38386090/ img

Authors show a retrospective, longitudinal study performed at a single tertiary institution. This study looked to determine whether a new 6 Fr or 8Fr polymer stent or Resonance® Cook Medical stent achieved a longer functional duration once the initial polymer ureteral stents failed in malignant ureteric obstruction. Patients with malignant ureteral obstruction generally have a poor prognosis, with a median survival of 3-6 months. However, relieving the obstruction may offer symptom relief and preserve renal function, which may offer these patients more oncological treatment options and possibly prolong their survival. A total of 46 patients (66 ureters) had ureteral stents placement for ureteral obstruction malignancy. From initial ureteral stent failure, 10 stents were changed to a new 6Fr polymer stent, 42 were changed to an 8Fr polymer stent and 14 were changed to a Resonance® 6Fr metallic stent. The median functional duration was 4.5 months for the new 6Fr polymer stent group, 4 months for the 8Fr polymer stent group and 14 months for the Resonance® stent group. Therefore, the Resonance® stent had the longest median functional duration of 14 months with statistical significance.

Since the insertion of the Resonance® stent in 2006, there have been many studies looking into the safety and efficacy of Resonance® stents and its use in malignant ureteral obstruction. The superiority of the Resonance® stent is thought to be due to the unique design of this stent. It is a metallic, MRI-compatible stent shaped in a tightly wound coil structure with no side hole openings at either end. The Resonance® stent is made of a nickel–cobalt–chromium–molybdenum alloy, making it resistant to corrosion and lithiasis formation, and therefore allows it to be changed less often than polymer stents, usually every 12 months. However, patients with very tight ureters and occluded lumens may encounter difficulty placing a Resonance® stent due to the larger sheath. Other studies looking at the safety and effectiveness of the Resonance® stent have shown an overall patency rate of approximately 80% with no major complications in the follow-up period.

In conclusion, the authors noted that the Resonance® stent is an effective option for patients with mailgn ureteral obstruction who have already failed a 6F polymeric stent and therefore should be considered as the subsequent intervention prior to progression to permanent percutaneous nephrostomy.

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