2025 Proffered Presentations
S289: THE COCHLEAR DIMPLE: A NOVEL LANDMARK FOR COCHLEAR PROTECTION DURING MIDDLE FOSSA SURGERY—A CADAVERIC LABORATORY INVESTIGATION
Ali Tayebi Meybodi, MD; Andrea L Castillo, MD; Ahmet Ozak, MD; Michael T Lawton, MD; Mark C Preul, MD; Barrow Neurological Institute
Background: Cochlear safety is paramount during middle fossa surgery due to the proximity of the cochlea to the adjacent potential surgical targets such as the internal auditory canal (IAC). Several methods were proposed for this purpose which are based on (1) general anatomic relationships and distance averages between the cochlea and adjacent structures or on (2) reconstruction of “safety lines” drawn between other structures around the cochlea and not involving the structure of interest, i.e., cochlea.
Objective: We assessed the applicability and safety of a direct cochlear localization landmark—the cochlear dimple, during middle fossa approach to the IAC.
Methods: Middle fossa approach was simulated in 16 cadaveric specimens. The middle fossa rhomboid was drilled to expose the anterior and superior aspects of the IAC and the cochlear dimple.
Results: 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, exposure of the cochlear dimple violated the cochlea. The configuration of 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.
Conclusions: Cochlear dimple is a direct anatomic landmark to localize the cochlea. It is the only available 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.
Figure 1. Steps of exposure of the cochlear dimple during middle fossa dissection in a cadaveric specimen.
Figure 2. Osseous anatomic foundations of cochlear dimple (green area).
Figure 3. Artist's illustration of the measurements performed in this study to delineate the microanatomy of the cochlear dimple.
Figure 4. Simulation of anterior petrosectomy on the right side of a cadaveric specimen and exposure of the cochlear dimple.
