MRI IAM — unenhanced high-resolution screen

Both internal auditory canals, cerebellopontine angles, membranous labyrinth and adjacent brainstem, with whole-brain sequences included to avoid missing an unrelated cause.

Typical, not policy

Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.

When to use it

Asymmetric sensorineural hearing loss, to exclude a vestibular schwannoma or other cerebellopontine angle lesion.
Unilateral tinnitus without a conductive or vascular explanation.
Unexplained unilateral vestibular failure.
Surveillance of a known small vestibular schwannoma on a watch-and-wait pathway.
Pre-cochlear-implant assessment of cochlear patency and cochlear nerve presence.

Technique

Core sequence is a submillimetre 3D heavily T2-weighted steady-state acquisition (CISS, FIESTA-C or equivalent), typically at around 0.4-0.8 mm, reformatted perpendicular to each nerve.
A coronal or axial T2 through the canals adds a second plane and improves confidence for small lesions.
Whole-brain axial T2 or FLAIR plus DWI to cover central causes of the symptom.
DWI is also the sequence that detects cholesteatoma when middle-ear disease is part of the question.

Where it goes wrong

Using standard 3-5 mm brain sequences and calling it an IAM study; small intracanalicular lesions are lost.
Not reformatting along the nerve, so a small lesion is only ever seen partial-volumed.
Assuming the unenhanced screen excludes everything: small intralabyrinthine and post-operative lesions are the recognised gap, and this is where contrast earns its place.
Susceptibility artefact from the petrous bone and from dental or surgical metal degrading the steady-state sequence.

Clinical questions that reach this study

Asymmetric sensorineural hearing loss — suspected vestibular schwannoma

Contrast

None

A heavily T2-weighted 3D acquisition alone detects the great majority of internal auditory canal and cerebellopontine angle lesions; gadolinium is not required for a screening question.

Acquisition

Breathing: Free breathing.
Preparation: Include the audiogram result and the side of the symptom — a bilateral symmetrical loss is a different question. Contrast is added only for specific sub-questions; do not assume it. Cochlear implants and some middle-ear prostheses need explicit device-conditionality checking before booking.

Safety checks this protocol carries

Derived from the contrast agent and phases above, not authored here — which is why they cannot drift apart from what the protocol actually does.

MR safety screening for implants and foreign bodies· radiographer at scan