Optimized evaluation of a pulsed 2.09 mu m holmium: YAG laser impact on the rat brain and 3 D-histomorphometry of the collateral damage

Since more than 20 years CO2 and Nd:YAC lasers are established in the micro surgery of the nervous system. CO2 lasers can be used handheld, but may be focused on the target area by mirror optics and sideports of the operating microscope's micromanipulator. Nd:YAG lasers have the disadvantage of deep penetration into the brain and provocation of a large collateral damage. Th e need is for a fibre conducted solid system for surgery in delicate areas as for brain stem surgery. Fibre conduction of near infrared lasers allows better exposure of the target area compared to hollow wave guides or mirror equipment. Fibres can be tapered and modified according to the purpose. Th e holmium:YAC (Ho:YAC) laser has acquired interest by introducing the syste m into microsurgery of parenchymal tissue. They have not been proven yet su fficiently for neurosurgical tasks, The effort to minimalize the collateral tissue damage has to be maximalized in the surgery of nervous tissue and f unctional low redundant brain stem or spinal cord tissue. Volumetric data m ay be more precise in comparison to depth and width data of the laser lesio n even when the different levels of the tissue interaction have to be analy zed for estimation of the real side effects in nervous tissue. We have used 50-800 ml delivered Ho:YAG single pulses in cortical areas of Sprague-Dawl ey rats and investigated the different lesion zones by volumetric data. The functional lesion zone was detected and measured by immunohistological sta ining of the heat shock protein HSP 72. For further reduction of the focus area, we have used tapered 400 to 200 mu m fibres.