Measurements of drill-induced temperature change in the facial nerve during mastoid surgery: a cadaveric model using diamond burs.

The purpose of this study was to investigate the changes in temperature in the facial nerve that occur during mastoid drilling by the facial recess approach and to confirm the beneficial effects of constant irrigation while drilling. Mastoid drilling was performed on human cadaveric temporal bones by means of 4-mm diamond burs with and without irrigation. There were 6 subjects in each group. Changes in facial nerve temperature were recorded on a continuous-output monitor. Significant changes were found in temperature for both the irrigation and non-irrigation groups (p < .0001). Constant irrigation minimized the rise in temperature. Facial recess drilling poses a potential threat to cranial nerve VII via thermal injury. The temperature elevation in the non-irrigation group was significantly greater than that in the irrigation group and was greater than the tolerable limits of peripheral nervous tissue. This finding supports the need for constant irrigation during the approach to the facial recess in mastoid surgery.