EXPERIMENTAL LASER-SURGERY IN OBLITERATED COCHLEAS

A pulsed holmium:YAG-laser (lambda=2120nm) was used to reopen the basa l turn of artificially obliterated human cochleas in freshly dissected cadavers for intracochlear insertion of the stimulation electrode of a cochlear implant under simulated surgical conditions. Laser energy w as transmitted through a 400 mum nylon fibre via the opened facial rec ess directly to the round window niche. At an energy level of 500 mJ/2 ,5 mus pulse, a repetition rate of 2 Hz, and an exposure time of 20-30 s, the photo-ablative mechanism of laser-bone interaction, which has only a limited thermal component, led to recanalisation of the basal t urn of the cochlea in a length of 8-10mm without damaging the surround ing structures. Light microscopic changes in the cochlea were evaluate d following laser recanalisation. The artificial bony occlusion and th e recanalised basal turn of the cochlea were visualised by means of co mputed tomography and histological thin section technique.