Anatomical Step-by-Step Dissection of Complex Skull Base Approaches for Trainees: Surgical Anatomy of the Translabyrinthine, Transotic, and Transcochlear Approaches

Introduction: Surgery of the cerebellopontine angle (CPA) is challenging. For select lesions in the CPA or invading the temporal bone, a translabyrinthine approach with or without transotic, or transcochlear extensions may be indicated. In this study, we aim to didactically describe the microsurgical and endoscopic-assisted anatomy of the translabyrinthine, transotic, and transcochlear approaches in an anatomically based, step-by-step manner, dedicated to facilitating the learning process for skull base surgical trainees. Nuances, indications, and limitations of the approaches are discussed.

Methods: Seven formalin-fixed, latex injected cadaveric specimens were utilized to demonstrate step-by-step dissections. Dissections were performed bilaterally, with combined translabyrinthine and transotic approaches on one side, and translabyrinthine and transcochlear approaches contralaterally. Each step was 3D photo-documented macroscopically and with endoscopic assistance on illustrative specimens.

Results: The translabyrinthine, transotic (includes closure of the EAC and preservation of the course of the facial nerve), and transcochlear (includes posterior transposition of the facial nerve) approaches provide wide access to the CPA and provide an increasingly deep and unobstructed exposure as structures of the temporal bone are removed/transposed. The key steps of the translabyrinthine approach include a wide cortical mastoidectomy; identification of the sigmoid sinus, Trautmann's triangle, and mastoid antrum; progressive drilling of the horizontal, posterior, and superior semicircular canals, respectively; identification of the vestibule; identification and 270-degree decompression of the internal auditory canal (IAC) dura; and opening of the IAC and posterior fossa dura.

Subsequently, to add the transotic extension before dural opening, the soft tissue of the external auditory canal (EAC) must be transected, everted, and closed; the skin of the ear canal and tympanic membrane are removed; the posterior wall of the EAC is then drilled to the level of the facial nerve in the fallopian canal, sacrificing the chorda tympani nerve; the malleus and incus are removed; the cochlea is drilled away exposing the petrous segment of the internal carotid artery. Drilling of troughs superior and inferior to the IAC proceeds as medial as possible before opening the dura.

To perform the transcochlear adjunct to the translabyrinthine approach, posterior fossa and IAC dura are opened, the facial nerve is transposed posteriorly after disconnecting the greater superficial petrosal nerve (GSPN) from the geniculate ganglion, the cochlea is drilled away—revealing the petrous segment of the internal carotid artery, further drilling follows its medial course to the clivus and inferior petrosal sinus.

Conclusion: Step-by-step surgical dissections are presented for the translabyrinthine, transotic, and transcochlear approaches, providing comparisons of exposure, limitations, and extent of dissection with the goal of facilitating and improving the learning process for skull base surgical trainees.

No conflict of interest has been declared by the author(s).

Publication History

Article published online:
01 February 2023