10Imaging in the work-up
Imaging is the third tier of the candidacy assessment, sitting alongside the audiological and medical work-ups. A high-resolution CT and an MRI of the temporal bones answer questions the audiogram cannot: is the cochlea open and normally formed, is it ossifying, and — most importantly — is there a cochlear nerve to stimulate? Most of what the scans reveal changes how the surgery is done rather than whether it is offered: an ossified cochlea needs a different array, a malformation an altered approach. But one finding can change the decision itself — a congenitally deficient or absent cochlear nerve leaves the implant with no target. This module covers what imaging adds to candidacy; the imaging chapter that follows treats it in full.
TWhy image before deciding
Imaging is not just surgical planning done early — it is part of candidacy. It confirms there is a cochlea to implant and a nerve to drive, detects anomalies that alter feasibility, and occasionally uncovers a reason the implant would fail. A candidacy decision made without imaging is incomplete.
CCT — the bony cochlea
High-resolution CT shows the bony labyrinth. Is the cochlea patent — a clear scala for a full insertion? Is there ossification, the new bone (often post-meningitic) that narrows the lumen and demands early surgery and a special array? Is the cochlea malformed— a common cavity, incomplete partition, or hypoplasia that changes the approach and the expected outcome? CT answers the anatomical “can we get an electrode in?”
CMRI — fluid and nerve
MRI complements CT by showing the fluid of the cochlea (confirming patency where CT is ambiguous) and, decisively, the cochlear nerve in the internal auditory canal. It also excludes retrocochlear pathology such as a vestibular schwannoma. For the candidacy question of is there a target for the implant?, MRI is the key test.
CSurgery vs decision
The useful distinction is between findings that change the operation and findings that change the decision. Ossification, malformation and an awkward anatomy change how the surgeon implants — and the device options (short, straight or split arrays) exist precisely to handle them. Only a deficient or absent cochlear nerve usually changes whether to implant, moving the decision toward an auditory brainstem implant. Imaging thus rarely vetoes candidacy, but it shapes almost every case that proceeds.
TCPatency grading and a neural proxy
Imaging is read systematically. The bony cochlea is given a patency grade (the Balkany–Dreisbach C0–C3 scale, from normal to bony obliteration) that predicts whether the array can be fully inserted and drives the surgical plan and device choice — a drill-out, a short or split array, or a scala-vestibuli insertion. A high grade after meningitis is also a reason to implant early, before the lumen closes.
MRI does more than confirm the nerve is present. High-resolution T2 imaging can measure the cochlear-nerve diameter, which correlates with the total spiral-ganglion-cell count — turning imaging into a neural-reserve proxy(“how much substrate,” not just “is there a nerve”).[1989] Imaging is even a device decision: a patient who will need lifelong MRI surveillance may be steered toward a removable- or non-magnetic-magnet implant, because a standard internal magnet can complicate future MRI.
How does this finding affect candidacy?
What do CT and MRI each contribute to the candidacy work-up?
Which imaging finding most often changes the candidacy decision (not just the surgery)?