Transcochlear

House and Hitselberger described the transcochlear approach to the skull base in 1976^[1]. It extends the translabyrinthine approach anteriorly by removing the cochlea and the bone around the internal auditory canal and petrous apex, after rerouting the facial nerve posteriorly out of its canal. The result is a wide lateral exposure of the petroclival junction and the ventral brainstem without retraction of the cerebellum or the temporal lobe.

• Large petroclival meningiomas, chordomas and chondrosarcomas in an ear with no useful hearing.
• Large epidermoids and other lesions of the petrous apex and ventral pons.
• Facial-nerve tumours that require nerve resection and grafting.

Because it sacrifices hearing and usually causes at least temporary facial weakness, it is reserved for patients with poor hearing or with lesions that cannot be reached safely by hearing-preserving approaches.

• Complete mastoidectomy and labyrinthectomy as in the translabyrinthine approach^[2].
• Close the external auditory canal and remove the middle-ear contents; this is the transotic variant when the facial nerve is left in its canal.
• Skeletonise the facial nerve from the IAC to the stylomastoid foramen, divide the GSPN and reroute the nerve posteriorly.
• Drill the cochlea and the bone of the petrous apex, exposing the petrous carotid artery anteriorly and the inferior petrosal sinus and clivus medially.
• Open the dura to expose the CPA and the petroclival region.
• Obliterate the cavity with fat and close the Eustachian tube^[3].

• Facial weakness after rerouting, often recovering to House–Brackmann grade III or IV^[4].
• Total ipsilateral deafness (planned).
• CSF leak through the Eustachian tube or the wound.
• Injury to the petrous carotid artery and the abducens nerve.