Image-guided Localization of the Internal Auditory Canal via the Middle Cranial Fossa Approach

Abstract

OBJECTIVE: We sought to determine the accuracy of an electromagnetic image guidance surgical navigation system in localizing the midpoint of the internal auditory canal (IAC) and other structures of the temporal bone through the middle cranial fossa approach. MATERIALS AND METHODS: Seven fresh cadaveric whole heads were dissected via a middle cranial fossa approach. High-resolution CT scans were used with an InstaTrak 3500 Plus electromagnetic image guidance system (General Electric, Fairfield, CT). We evaluated the accuracy of identifying several middle cranial fossa landmarks including the midpoint of the IAC; the labyrinthine segment of the facial nerve; and the arcuate eminence, the carotid artery, and foramen spinosum. RESULTS: We were able to identify the middle of the IAC within 2.31 mm (range 0.65-7.52 mm, SD 2.39 mm). The arcuate eminence could be identified within 1.86 mm (range 1.49-2.37 mm, SD 0.36 mm). We noted some interference when the handpiece was within 6 to 8 cm of the microscope. CONCLUSION: Although computer-aided navigational tools are no substitute for thorough knowledge of temporal bone anatomy, we found the InstaTrak system reliable in identifying the midpoint of the IAC to within 2.4 mm through a middle fossa approach.