EFFECT OF BALLOON DILATION OF URETER ON UPPER TRACT DYNAMICS AND URETERAL WALL MORPHOLOGY

Sixteen male Yucatan minipigs underwent balloon dilation of the right ureterovesical junction (UVJ) and lower ureter to twice its normal cal iber. With the bladder open, bilateral upper tract dynamics measuremen ts under different perfusion rates (0.5, 2, and 4 ml/min) were recorde d predilation, immediately after dilation, and 1, 2, 3, 4, and 6 weeks after dilation. Immediate and late antegrade nephrostograms, suprapub ic cystograms, and right antegrade nephrostograms (oblique view) were taken. In the chronic experiment, no difference in renal pelvic pressu re (P(pvs)) was detectable between the control and dilated sides immed iately after dilation. Only at 4 ml/min was there a statistically sign ificant increase in the P(pvs) of the dilated ureter 1 week after dila tion when compared with the controls. At 2 weeks, this obstructive cha nge had disappeared. At 3, 4, and 6 weeks, P(pvs) of the dilated urete r declined progressively in comparison with the control side, but the difference was not statistically significant. At 6 weeks, P(pvs) of th e dilated ureter decreased significantly compared with predilation rea dings only at 4 ml/min. Immediate antegrade radiologic evaluation reve aled that 69% of the experimental animals had no extravasation, while 31% showed variable degrees of extravasation, which disappeared comple tely on late antegrade nephrostograms (6 weeks). Grade 2 reflux occurr ed 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 nonh omogeneous pattern of ureteral damage, ranging from total rupture to m uch less dramatic injury. At 6 weeks, there was nearly complete repair of the ureter. In an acute experiment, three New Hampshire pigs under went bilateral balloon dilation, with the right ureter being-dilated t o twice its normal caliber and the left ureter dilated threefold. The ureter tolerated twofold dilation without muscular rupture whereas thr eefold dilation resulted in complete rupture. These results indicate t hat it is safe to dilate the ureter up to twice its normal caliber. Th e damaged ureter heals with new or reorganized muscle without strictur e formation.