Evaluation of superficial papillary ablation by endoscopic lasers in an ex vivo kidney model.
OBJECTIVE
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.


METHODS
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.


RESULTS
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 (<20 cell layers) but more extensive coagulation necrosis, whereas no histologic effects were observed at the same energy level without contact. In contrast, independent of delivered energy but dependent on time, Ho:YAG laser application caused pure tissue loss without relevant coagulation necrosis. The generation of small lesions (6-10 cell layers) without tissue contact was possible at energy levels under 2 J.


CONCLUSIONS
Selective superficial papillary cell ablation is possible. Low-energy Nd:YAG treatment in the contact mode and Ho:YAG treatment in the noncontact mode led to superficial vaporization with no (Ho:YAG) or minimum (Nd:YAG) coagulation defects.
Knoll
Thomas
T
Department of Urology, University Hospital Mannheim, Germany. thomas.knoll@uro.ma.uni-heidelberg.de
Michel
Maurice Stephan
MS
Cueva-Martínez
Armando
A
Spahn
Martin
M
Bross
Stephan
S
Alken
Peter
P
Köhrmann
Kai-Uwe
KU
D000818:Animals; D002114:Calcinosis / Q000473:pathology / Q000601:surgery; D004724:Endoscopy; D007669:Kidney Calculi / Q000473:pathology / Q000517:prevention & control* / Q000601:surgery; D007679:Kidney Medulla / Q000473:pathology* / Q000601:surgery*; D053685:Laser Therapy / Q000295:instrumentation / Q000379:methods*; D019060:Minimally Invasive Surgical Procedures; D009336:Necrosis; D055502:Secondary Prevention; D013552:Swine; D019459:Urothelium / Q000473:pathology / Q000601:surgery