LOCATING THE INTERNAL AUDITORY-CANAL DURING THE MIDDLE FOSSA APPROACH- AN ALTERNATIVE TECHNIQUE

Options for the surgical exposure of the internal auditory canal (IAC) include the translabyrinthine, retrosigmoid, and middle fossa approac hes. Of the three, the anatomical reference points to the IAC are most subtle when it is exposed from above. The classically described metho ds for localizing the canal during the middle fossa approach direct th e surgeon's attention initially towards the lateral extremity of the c anal. a location where the margin for error is at its minimum. The coc hlea, 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 t he advantage of locating the canal away from these vulnerable structur es in an area where there is a relatively wide margin of safety. In th is medially directed technique, drill excavation is commenced in the p etrous apex well anterior to the anticipated location of the porus. On ce the medial portion of the IAC has been well defined, dissection can proceed laterally by removal of bone directly over the known course o f the cana. This strategy minimizes the risk of injury to the viscera of the petrous bone.