Evaluation of a dissolvable ureteral drainage stent in a Swine model

Ureteral stents are commonly placed after routine ureteroscopic procedures to prevent acute ureteral obstruction. However, stents can cause significant symptoms, may require a secondary procedure for removal and may possibly be forgotten. Toward this end a temporary ureteral drainage stent capable of dissolving spontaneously was developed to obviate the problems associated with more commonly used stents.

We evaluated 3 stents of various compositions in a swine model. These stents were composed of dense dissolving material with and without radiopaque filling (dense filled and dense unfilled, respectively) and soft material with radiopaque filling (soft filled). Standard soft hydrogel coated plastic stents served as controls. Three female swine were placed into 4 groups each, including group 1-dense unfilled versus standard stents with harvest at day 7, group 2-dense unfilled versus standard stents with harvest at day 3, group 3-dense filled versus dense unfilled stents with harvest at day 2 or 3 and group 4-soft filled versus dense unfilled stents with harvest at day 2 or 3. Stents were placed bilaterally. The radiopaque quality of stent fragments on plain x-ray of the kidneys, ureters and bladder, and excretory urography, stent condition and histological changes of the urinary tract were compared among the groups.

Successful cystoscopic placement of all stents was achieved. The standard stent was present at autopsy in all animals in group 1, although the dense unfilled stent was absent in group 1 at day 7. In group 2 the standard stent was in position but the dense unfilled stent was fragmented in 2 of the 3 animals and absent in 1. In groups 3 and 4 (dense filled versus dense unfilled and soft filled versus dense unfilled, respectively) all stents were fragmented in similar fashion on harvest day 2 or 3. Standard stents and filled stent fragments were evident on imaging, although dense unfilled stents were not discernible. Histological testing revealed inflammatory changes associated with all stents with no significant difference among stent types.

These temporary drainage stents appeared to dissolve in benign fashion, as evidenced by the appearance of the collecting system on excretory urography and by histological changes. In addition, inflammatory changes throughout the urinary tract were similar for each stent evaluated. Further analysis is warranted in human subjects to assess the exact time of stent retention, potential adverse symptoms, stent fragment passage and safety.