2Imaging as the surgical blueprint
Once a patient is judged a candidate, imaging turns the decision into a plan. A high-resolution CT and an MRI of the temporal bone answer two kinds of question at once: the candidacy question — is there a cochlea to implant and a nerve to drive? — and the surgical question — what cochlea, nerve, facial canal and mastoid will the surgeon actually meet? The two modalities are complementary, CT reading bone and MRI reading fluid and nerve, and most centres obtain both. A useful way to keep the whole work-up in order is a sequence of three questions, and a small number of findings act as absolute gates that turn a cochlear implant into an auditory brainstem implant. This module frames the chapter; the brief candidacy-level imaging summary lives in the Candidacy chapter.
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.
FTwo jobs at once
Preoperative imaging serves two purposes simultaneously: finishing candidacy (does an implantable cochlea and a cochlear nerve exist?) and planning the operation (what anatomy will the surgeon meet?). It is the bridge from the candidacy decision to the operating theatre.[2022]
FThree sequential questions
Fishman and Heman-Ackah's framework keeps the work-up disciplined: (1) is there any anomaly that precludes implantation; (2) is the cochlear lumen obstructed by ossification or fibrosis; (3) is there anything that will complicate surgery or later management? Each question points to the modality that answers it and the action it triggers.
TCT and MRI are complementary
CT and MRI are not alternatives. CT excels at the bony detail — the otic capsule, ossicles, windows, air spaces and facial canal — while MRI shows the membranous labyrinth, the cochlear nerve, early fibrosis and retrocochlear pathology. Crucially, both assess form, not function: a stimulable pathway must still be inferred from residual hearing and objective measures (Chapter 27).
CThe absolute gates
A few findings are absolute imaging gates: complete cochlear aplasia (no cochlea) and cochlear-nerve aplasia (no nerve) both contraindicate a cochlear implant and redirect toward an auditory brainstem implant. Imaging also arbitrates side selection — the cochlea with the least ossification and the most favourable nerve and access is usually chosen when audiometric factors are equal.
FChapter roadmap
| Movement | Modules | What they cover |
|---|---|---|
| The philosophy | 1 | The Rational Checklist — MRI-predominant, selective HRCT, and the two checklists this chapter applies. |
| How to image | 3–5 | CT technique, MRI sequences and the nerve view, and normal anatomy. |
| The cochlea & nerve | 6–9 | Malformations, incomplete partition and EVA, the cochlear nerve and IAC, ossification and patency. |
| The surgical field | 10–12 | The facial nerve, the middle ear and vessels, and cochlear measurements for the array. |
| Around surgery & report | 13–18 | Paediatric imaging, intra- and post-operative imaging, MRI compatibility, emerging modalities, and the structured report. |
The whole chapter is read through one lens — the Rational Checklist of Module 1: screen every candidate with MRI, reserve HRCT for the candidates who need it, and work each scan as a fixed sequence so candidacy, surgical risk and electrode choice fall out of the same structured look.[2026]We then begin with how the scan is actually made — CT technique (Module 3).
What are the two jobs preoperative imaging does?
What two jobs does preoperative imaging do?
Which findings are absolute imaging gates that redirect to an ABI?