RESUMO
INTRODUCTION: In CO2 laser myringotomy, a self-healing perforation is typically created in the lower anterior quadrant. A prominent anterior meatal wall may cover that quadrant and necessitate dorsal perforation of the eardrum. This study orientationally assessed the risk of damaging the round window membrane (RWM) when applying the laser in dorsal eardrum areas. MATERIALS AND METHODS: The round window was exposed by otomicrosurgery in 61 human petrous bone specimens. CO2 laser myringotomy was previously performed with twice the standard power (25 W, 180 ms, 2.2 mm) in the lower posterior quadrants of 25 specimens, the beam being applied directly to the round window niche in five specimens, and the effect of the laser radiation was documented. The RWM was subsequently exposed in all petrous bones, and the angle correlation of the membrane to the direction of the laser beam was digitally measured. RESULTS: The laser did not damage the membrane of the round window in any of the cases. The angle between the RWM and the external auditory meatus was below 30 degrees in 97% of the petrous bones and thus had a nearly parallel course. CONCLUSION: Localization of the window caudodorsal to the meatal wall, bone overhanging the membrane, mucosal duplications, and membrane alignment nearly parallel to the laser beam make it virtually impossible to reach this membranous structure with the CO2 laser.