Surgical Exposure of the Proximal Internal Auditory Canal: An Anatomosurgical Comparison of Retrosigmoid and Middle Fossa Transpetrosal Corridors

Introduction: The internal auditory canal (IAC) can be accessed through several different anterolateral, lateral, or posterolateral surgical corridors. Surgically accessing lesions occupying the most proximal aspect of the IAC can be especially challenging through any of these corridors due to its deep-seated location in the anatomically complex temporal bone. We describe the surgical anatomy of the proximal IAC and analyze the surgical exposure and maneuverability provided by hearing-sparing retrosigmoid and middle fossa anterior transpetrosal (AT) surgical approaches.

Methods: Retrosigmoid and middle fossa AT approaches and opening of the IAC were performed on cadaveric specimens to evaluate exposure of the proximal IAC and maneuverability within. To quantify exposure, the IAC was divided into anatomical quadrants using two orthogonal planes bisecting the long axis of the IAC axially and sagittally. The IAC was then subdivided into three segments parts from medial to lateral—prelabyrinthine, labyrinthine, and postlabyrinthine—using two imaginary lines, passing through the most medial portion of the posterior semicircular canal and passing through the most lateral portion of the lateral semicircular canal, respectively. Following exposure of the IAC in the AT approach and complete skeletonization of the labyrinth, a high intensity endoscope light was used to transilluminate the dura of the IAC to visualize the amount of the IAC that could be safely drilled through a retrosigmoid approach. Neuronavigation was then used to measure, document, and correlate the boundaries of this area.

Results: The AT approach provided wide exposure of the anterosuperior and posterosuperior quadrants of the IAC, while the retrosigmoid approach provided good exposure of the prelabyrinthine segment extending partially to the inferior quadrants. Using transillumination and neuronavigation, a small safe region of drilling via the retrosigmoid corridor was identified and verified.

Conclusion: The retrosigmoid approach can be used to access the proximal IAC in cases of small tumors wherein hearing preservation is the goal. Lesions located in the prelabyrinthine segments and expending circumferentially around the cranial nerve VII–VIII complex are amenable to resection via the retrosigmoid approach, whereas tumors involving multiple IAC segments or either the labyrinthine or postlabyrinthine segment

Publication History

Article published online:
12 February 2021