Effect of Balloon Dilation of Ureter on Upper Tract Dynamics and Ureteral Wall Morphology

Abstract

Sixteen male Yucatan minipigs underwent balloon dilation of the right ureterovesical junction (UVJ) and lower ureter to twice its normal caliber. With the bladder open, bilateral upper tract dynamics measurements under different perfusion rates (0.5, 2, and 4 ml/min) were recorded predilation, immediately after dilation, and 1,2, 3, 4, and 6 weeks after dilation. Immediate and late antegrade nephrostograms, suprapubic cystograms, and right antegrade nephrostograms (oblique view) were taken. In the chronic experiment, no difference in renal pelvic pressure (P_pvs) was detectable between the control and dilated sides immediately after dilation. Only at 4 ml/min was there a statistically significant increase in the P_pvs of the dilated ureter 1 week after dilation when compared with the controls. At 2 weeks, this obstructive change had disappeared. At 3, 4, and 6 weeks, P_pvs of the dilated ureter declined progressively in comparison with the control side, but the difference was not statistically significant. At 6 weeks, P_pvs of the dilated ureter decreased significantly compared with predilation readings only at 4 ml/min. Immediate antegrade radiologic evaluation revealed that 69% of the experimental animals had no extravasation, while 31% showed variable degrees of extravasation, which disappeared completely on late antegrade nephrostograms (6 weeks). Grade 2 reflux occurred in 33% of the experimental animals at 1 week and had disappeared at 6 weeks. Histologic examinations at 1, 2, and 3 weeks revealed a nonhomogeneous pattern of ureteral damage, ranging from total rupture to much less dramatic injury. At 6 weeks, there was nearly complete repair of the ureter. In an acute experiment, three New Hampshire pigs underwent bilateral balloon dilation, with the right ureter being dilated to twice its normal caliber and the left ureter dilated threefold. The ureter tolerated twofold dilation without muscular rupture whereas threefold dilation resulted in complete rupture. These results indicate that it is safe to dilate the ureter up to twice its normal caliber. The damaged ureter heals with new or reorganized muscle without stricture formation.