Pre-operative Screening and Manual Drilling Strategies to Reduce the Risk of Thermal Injury During Minimally Invasive Cochlear Implantation Surgery

Abstract

This article presents the development and experimental validation of a methodology to reduce the risk of thermal injury to the facial nerve during minimally invasive cochlear implantation surgery. The first step in this methodology is a pre-operative screening process, in which medical imaging is used to identify those patients that present a significant risk of developing high temperatures at the facial nerve during the drilling phase of the procedure. Such a risk is calculated based on the density of the bone along the drilling path and the thermal conductance between the drilling path and the nerve, and provides a criterion to exclude high-risk patients from receiving the minimally invasive procedure. The second component of the methodology is a drilling strategy for manually-guided drilling near the facial nerve. The strategy utilizes interval drilling and mechanical constraints to enable better control over the procedure and the resulting generation of heat. The approach is tested in fresh cadaver temporal bones using a thermal camera to monitor temperature near the facial nerve. Results indicate that pre-operative screening may successfully exclude high-risk patients and that the proposed drilling strategy enables safe drilling for low-to-moderate risk patients.

Clinical Implementation of Second-generation Minimally Invasive Image-guided Cochlear Implantation Surgery

“…The microstereotactic frame approach was implemented before the multiarticulated arm robot approach but had one patient in the first cohort of nine patients who awoke from general anesthesia with a facial nerve paresis secondary to heat generation during drilling. Corrective action was taken to prevent this complication from recurring including redesigning the drill bit and implementing incremental peck drilling with continuous irrigation which was shown in temporal bones to result in decreased temperatures near the facial nerve as compared with the previous technique (3).…”

A worthy technique for transcanal drilling during endoscopic ear surgery

“…This temperature and its exposure duration maintain such a inter relationship that same thermal effect can be produced by changing either of these two. 3,4 This relationship was expressed through a complicated mathematical equation which stated that if the temperature was increased by one degree Celsius, the exposure time must be decreased by a factor of two for the same thermal effect. 4 This sort of mathematical equation has been used in Cancer Radiotherapy to determine the thermal dose in order to avoid peripheral nerve injury.…”

“…This study although neither mentioned a specific time interval nor recorded the time but this unrecorded time interval allowed cooling down the drilling area as well as the drill burr. The study conducted by Neal P Dillon et al 3 showed that after stopping the drilling for approximately 30 s, the raised temperature of drilled area would return to within 3 C of body temperature.…”