THE INTERACTION OF LASER ENERGY WITH URETER TISSUES IN A LONG-TERM INVESTIGATION

This study investigates tissue responses after laser irradiation of th e rabbit ureter, which serves as an experimental model for rectourogen ital fistulae of children. Twenty-five rabbit ureters were irradiated intraluminally by a Nd:YAG laser 1320 nm (2 Watt, 20 seconds and 3 Wat t, 8 seconds) via an applicator with radialsymmetrical light distribut ion. Immediately, 2 weeks, 4 weeks, 8 weeks, and 16 weeks after irradi ation, the ureters were X-rayed with contrast solution and prepared fo r light and transmission electron microscopy. For the parameters emplo yed, no apparent morphological differences could be observed. Immediat ely, the central laser zone showed a transmural thermonecrosis prevail ed by cellular destruction, condensed ground substance and occlusion o f most vascular lumina. Peripheral laser zones displayed urothelial va cuolations. Between 2 and 16 weeks, urothelial regeneration and ingrow th of granulation tissue caused a luminal stenosis or occlusion follow ed by transformation into scar tissue. In some peripheral laser zones, a hydroureter with marked luminal dilatation developed. We conclude t hat the ureter is occluded if the expanding force of the growing scar tissue exceeds the hydrostatic pressure of the obstructed urine. A las er occlusion of rectourogenital fistulae will be easier to achieve sin ce fistula occlusion does not entail an obstruction of the urine flow.