Thermal injury to the intratemporal facial nerve following CO2 laser application

The carbon dioxide (CO2) laser has been advocated for removal of diseased tissue from the middle ear cleft. The effect of CO2 electromagnetic radiation on mucosa and the otic capsule, however, is thermal, and the dissipation of heat into tissue surrounding the area of impact is potentially deleterious to normal structures. A CO2 laser with a 150-microns spot size at a focal length of 300 mm and a power output ranging from 0.25 to 1.5 watts was used to vaporize the mucosa overlying the horizontal portion of the fallopian canal with pulses of 0.2- to 0.5-second duration. Damage to the facial nerve was directly related to laser pulse energy and was most pronounced adjacent to the area of impact but spread distally and proximally at higher energy levels because of the heat conductivity of the bony fallopian canal. Facial movement was an unreliable indicator of injury during the vaporization process. Because the application of electromagnetic energy over the fallopian canal can result in facial paralysis, a knowledge of facial nerve anatomy remains a prerequisite to the safe extirpation of diseased tissue in the middle ear cleft.