Effects in laser-assisted stapedotomy

Abstract

In patients with otosclerosis, the stapes fixates in the oval window, resulting in a conductive hearing loss. A stapedotomy can be performed to restore hearing. During this surgery a small hole is created in the footplate of the stapes, by a micropick instrument or laser. Making a fenestration is not without risks, damage can occur to the inner ear structures, resulting in vertigo, tinnitus and hearing loss. A non-contact method, by using a laser, seems preferable. Nonetheless, the laser use is associated with side effects, as a result of heating, mechanical and acoustic effects. These effects differ between lasers and can be predicted by the wavelength and absorption spectrum of the laser. The aim of this thesis was to explore the effects of different lasers used in stapedotomy in order to identify the best one. In current literature, there is only limited evidence available. The laser technique gives comparable hearing results, measured by Air Bone Gap closure, compared to the conventional technique. Adverse events as fractured footplate and sensorineural hearing loss (SNHL), however, are higher in the conventional technique. Comparing different lasers shows a slight favor for CO2, laser, but differences are small. Four lasers were compared in this thesis, the KTP, Diode, CO2,, and Thulium laser. Effects to inner ear structures, as thermal, mechanical and acoustic effects, were compared in an inner ear model. To capture effects invisible to the human eye, specialized imaging techniques, as the high speed Schlieren imaging, were used. To answer the questions whether the found effects could be damaging to inner ear function, hearing was evaluated in the guinea pig after cochleostomy by the different lasers. Also, a nonrandomized comparison of the Thulium and CO2 laser in patients undergoing a stapedotomy for otosclerosis was performed. Thulium laser shows a poor performance compared to KTP, Diode and CO2 lasers in the inner ear model and animal model experiments. Heating patterns for the Thulium laser are more profound and extensive bubble formation occurs. Also, the Thulium laser makes more sound than the other lasers, although it need to be said that all lasers generate less sound than a conventional microdrill. In the guinea pig, hearing thresholds deteriorated most for Thulium laser, compared to the controle group. Differences were, however, small. In the patient serie, there was a higher percentage of patients with substantial SNHL and tinnitus in the Thulium group compared to CO2 group. Taken all these results into account, it is thus advisable not to use the Thulium laser in stapedotomy. The KTP, Diode and CO2 lasers seem to be safe when used in stapedotomy.