Evaluation of superficial papillary ablation by Endoscopic lasers in an ex vivo kidney model

Endoscopic examinations of stone-forming kidneys show a coincidence of plaques and microliths on the surface of and within papillary epithelial tissue. These calcifications are thought to be precursors of calcium oxalate urolithiasis. We hypothesized that minimally invasive endoscopic laser ablation of microliths and necrotic cell layers enables epithelial regeneration and prevents recurrent urolithiasis. The aim of this study was to determine the most suitable laser type and dose intensity for selective superficial cell ablation. Conventional Nd:YAG (1-40 W) or Ho:YAG (0.5-3 J/single impulse) lasers were used endoscopically on an ex vivo blood-perfused porcine kidney model. Defined doses were applied to the papillary surface in the contact and noncontact modes for 10 to 30 seconds. Papillae were excised after treatment and histopathologically analyzed in continuous sections. Lesions were microscopically assessed with the aid of a Leica Quantimed computer program. Depending on the time and dose, vaporization by the Nd:YAG laser caused large tissue defects and coagulation necrosis at energy levels over 5 W (contact and noncontact mode). Lower energy levels with tissue contact produced only superficial cell defects (