Modality
Magnetic Resonance Imaging
MRI is the modality of choice whenever the bedside cannot exclude a central or retrocochlear cause. Its strength is soft-tissue contrast across the brainstem, cerebellum, cranial nerves and inner ear; its weakness is access, cost, and contraindications such as cardiac devices.
When MRI is the right answer
Reach for MRI when you suspect a cerebellar or brainstem stroke, when a schwannoma or other retrocochlear cause is on the table, or when episodic vertigo in a young person raises the possibility of demyelination. MRI also provides the high-resolution sequences that delineate the internal auditory canal and membranous labyrinth.
The acute vestibular syndrome workhorse is DWIwith the corresponding ADC map. Restricted diffusion confirms acute infarction; reading the two together filters out the T2-shine-through false positives.1Beware the documented false-negative rate of early DWI for small posterior fossa strokes — a single negative scan in the first 24–48 h does not exclude infarction.2,3
For the IAC and cerebellopontine angle, FIESTA / CISSthin-slice T2 sequences delineate the seventh and eighth cranial nerves against bright CSF. Gadolinium-enhanced T1 then highlights schwannomas, meningiomas and active demyelinating plaques. For demyelination across the brain and cord, 3D-FLAIR is the standard, with post-Gd T1 to find active lesions.4
Endolymphatic hydrops can now be imaged directly. Delayed 3D-FLAIR acquired 4 hours after intravenous (or 24 hours after intratympanic) gadolinium resolves the perilymphatic from the endolymphatic compartment, allowing grade-based reporting of saccular and cochlear hydrops.5
Practically, the AVS MRI request should specify “MRI brain with DWI / ADC, FLAIR, post-Gd T1, plus thin-slice FIESTA through the IAC” if there is accompanying hearing change. Add MRA / CTA of the posterior circulation if vascular substrate is plausible. Repeat at 72 h if clinical suspicion outweighs a negative early scan.3
In the chronic / functional vestibular syndromes (PPPD, MdDS) structural MRI is typically normal — its value is to exclude alternatives, not to confirm the diagnosis. Functional MRI is covered separately under fMRI & PET.
The sequences — at a glance
The figure below pairs each sequence with its tissue read-out and the clinical question it best answers. The slice illustrations are schematic — not derived from any patient — and intended to clarify the contrast logic rather than substitute for radiological training.
Schematic axial cut — not derived from a real patient.
Same lesion, four sequences
The same finding does not look the same in every sequence. Pick a lesion and see which of DWI, FLAIR, post-Gd T1 and FIESTA actually reveals it — the green tick marks the sequence that earns its place in the protocol.
The internal auditory canal — what we are looking at
Four nerves run together through the IAC: facial (VII), cochlear, superior vestibular and inferior vestibular. Schwannomas almost always arise from the superior vestibular nerve; they fill the canal first, then bulge into the cerebellopontine angle. Drag the stage slider to watch the growth pattern that produces the classical “ice-cream cone.”
Schematic — not derived from a real patient scan. The vestibular schwannoma classically arises from the superior vestibular nerve's Schwann cells. Growth fills the IAC first, then bulges into the CPA cistern; the resulting profile is the “ice-cream cone.”
MRI cautions and contraindications
- Cardiac devices and ferromagnetic implants — non-MR-conditional pacemakers and certain cochlear implants preclude MRI; choose CT alternatives or MR-conditional protocols when essential.
- Gadolinium— modern macrocyclic agents are safe in most patients; severe renal impairment (eGFR < 30) and prior reactions require careful weighing.
- Claustrophobia, agitation, vomiting — limit early-acquisition quality; consider sedation or short-protocol stroke MRI in the unwell patient.
- Time and access — out-of-hours MRI access is the practical bottleneck in most centres; a clear protocol minimises wasted acquisitions.