Locating the Internal Auditory Canal during the Middle Fossa Approach

Abstract

Options for the surgical exposure of the internal auditory canal (IAC) include the translabyrinthine, retrosigmoid, and middle fossa approaches. Of the three, the anatomical reference points to the IAC are most subtle when it is exposed from above. The classically described methods for localizing the canal during the middle fossa approach direct the surgeon's attention initially towards the lateral extremity of the canal, a location where the margin for error is at its minimum. The cochlea, semicircular canals, and geniculate ganglion of the facial nerve are all positioned in close proximity to the fundus of the canal. An approach which is initially directed towards the porus acusticus has the advantage of locating the canal away from these vulnerable structures in an area where there is a relatively wide margin of safety. In this medially directed technique, drill excavation is commenced in the petrous apex well anterior to the anticipated location of the porus. Once the medial portion of the IAC has been well defined, dissection can proceed laterally by removal of bone directly over the known course of the canal. This strategy minimizes the risk of injury to the viscera of the petrous bone.

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