Long-term effects of ureteric stent after ureteric dilation.

Balloon dilation of the right ureterovesical junction (UVJ) and distal ureter to three times its normal caliber was performed in 12 pigs. A right double-J (D-J) stent was inserted after dilation in 6 pigs. Bilateral upper tract dynamics with different perfusion rates (0.5, 2 and 4 ml. per minute) were recorded before dilation, immediately after dilation, and then 4 and 7 weeks after dilation. Immediate and late antegrade nephrostograms as well as suprapubic cystograms were taken. Grade 3 reflux occurred in 100% of animals at 7 weeks on the dilated, stented ureter and no reflux on the dilated, nonstented ureter. At 7 weeks on the dilated, stented side, significant growth (> 100,000, colonies) of Pseudomonas species was noted in all animals. Creatinine clearance was significantly reduced on the dilated, stented side when compared to the dilated, nonstented side at 7 weeks. Histologic examination of the dilated, stented and dilated, nonstented ureters at 4 weeks revealed a segmental muscular defect with muscular regeneration starting from the edge of the defect, particularly in the innermost region. At 7 weeks, there was a more advanced, but similar, pattern of muscular regeneration in both groups. However, at 7 weeks, metaplastic changes of the ureter and chronic pyelonephritis were evident on the dilated, stented ureter. Electron microscopy showed that myofibroblasts played a major role in the healing process with new muscle formation. At 4 weeks, no significant morphologic difference was found between the dilated, stented and dilated, nonstented ureters. At 7 weeks, however, it appeared that the ureteric stent resulted in damage and deterioration of renal function without affecting muscular regeneration of the ureter. We conclude that the changes observed could be entirely due to the infection associated with the stent rather the stent itself.