INTRACRANIAL-PRESSURE WAVES GENERATED BY HIGH-ENERGY SHORT LASER-PULSES CAN CAUSE MORPHOLOGICAL DAMAGE IN REMOTE AREAS - COMPARISON OF THE EFFECTS OF 2.1-MU-M HO-YAG AND 1.06-MU-M ND-YAG LASER IRRADIATIONS IN THE RAT-BRAIN

Background and Objective: Histological effects of 2.1-mu m Ho:YAG and 1.06-mu m Nd:YAG laser pulses were compared in the rat brain, with spe cial regard to areas remote from the irradiated site. Study Design/Mat erial and Methods: Laser pulses were delivered through a 0.6-mm glass fiber, the tip of which was either introduced into the caudate nucleus (application mode I), or held at a 2-mm distance above the exposed in tact dura. In the latter case, the space between the dura and the fibe r tip was filled either with physiological saline (application mode II ) or with air (application mode III). Results: In application modes I and II, but not in application mode III, Ho:YAG; laser pulses of 1.5 J and 200 mu s, but not Nd:YAG laser pulses with the same parameters, i mmediately caused morphological damage to a considerable number of neu rons and axons randomly distributed among apparently normal ones in ce rtain areas remote from the irradiated site. A decrease in the energy and an increase in the length of the pulses lowered the incidence of t he remote morphological damage. Conclusion: This novel finding may imp ose limits on the application of Ho:YAG; lasers in human endoscopic ne urosurgery. (C) 1997 Wiley-Liss, Inc.