The Cochlear Dimple: A Novel Landmark for Cochlear Protection During Middle Fossa Surgery-A Cadaveric Laboratory...

Cochlear safety is paramount during middle fossa surgery because of the proximity of the cochlea to adjacent potential surgical targets such as the internal auditory canal (IAC). Several proposed methods are based on general anatomical relationships and distance averages between the cochlea and adjacent structures or reconstruction of lines drawn between other structures around the cochlea. We assessed the feasibility and safety of using the cochlear dimple as a direct cochlear localization landmark during a middle fossa approach to the IAC.

The middle fossa approach was simulated in 13 fresh cadaveric temporal bone specimens and 2 intact heads (4 sides). The middle fossa rhomboid was drilled to expose the anterior and superior aspects of the IAC and the cochlear dimple.

The cochlear dimple was identified as a triangular depression in the distal dura of the anterior IAC with a mean distance of 3.2 mm from the laterally located cochlea. In no specimen did exposure of the cochlear dimple violate the cochlea. The cochlear dimple was identifiable in all specimens, and it was created by the divergence of the distal intracanalicular course of the facial and cochlear nerves near the IAC fundus.

The cochlear dimple is a direct anatomical landmark that can be used to localize the cochlea. It is the only landmark whose establishment is not contingent on the identification of any other structure. It may be used as an additional measure to protect the cochlea during middle fossa surgery.