11Middle ear, mastoid & vascular anatomy for the approach
The cochlea is the destination, but the surgeon has to get there, and imaging maps the route. The transmastoid facial-recess approach to the round window runs through a narrow corridor whose width depends on how well the mastoid is pneumatised and how deep the facial recess is — and which can be crowded or threatened by a wayward vessel. A high or dehiscent jugular bulb can sit over the round-window niche; an anteriorly-placed sigmoid sinus narrows the path; and an aberrant or dehiscent carotid artery, lying close to the anterior basal turn, must be known before any drill-out to avoid catastrophe. Chronic ear disease, a previous cavity or a fracture can rewrite the landmarks entirely. This module reads the field the surgeon will work in.
Imaging note
Representative CT and MRI images for this chapter are being added soon. The interactive figures here are original schematic teaching diagrams; to respect copyright we do not reproduce third-party radiographs.
TThe operative corridor
Imaging defines the operative corridor: the degree of mastoid pneumatisation (and marrow content) and the depth of the facial recess determine access to the promontory and round window via the transmastoid approach. Confirm the mastoid and middle ear are large and aerated enough to reach the promontory.[2022]
CVascular variants to report
Several vascular variants must be reported preoperatively: an anteriorly-displaced or high sigmoid sinus, a high-riding jugular bulb (~6%) or diverticulum that can overlie the round-window niche, a dehiscent jugular bulb (~1.6%), and an aberrant or dehiscent internal carotid artery— which lies close to the anterior basal turn and must be recognised before drill-out. Also note a low-lying tegmen, asymmetric petrous-apex pneumatisation and Korner's septum.
CRound window & access
Define round-window patency and position — it may be absent or displaced posteriorly/superiorly in malformed ears — and, where a drill-out is planned, measure the round-window-to-carotid distance in advance from CT.
CChronic disease & altered anatomy
Chronic otitis media or cholesteatoma is not an absolute contraindication but may force staged surgery — canal-wall-up, or a subtotal petrosectomy with blind-sac closure and fat obliteration before implanting into a stable cavity. A prior canal-wall-down mastoidectomy, a temporal-bone fracture or a previous cavity distort the landmarks and may shift the choice of ear (Surgery chapter; Module 18).
What is the significance?
What determines access in the transmastoid facial-recess approach?
Which vascular variant most demands recognition before a drill-out?