Differential & action
Imaging decisions
The dizzy patient does not need a scan. The dizzy patient with a central HINTSpattern, an unexplained syndrome, or a vascular red flag does. Choosing the right modality saves time and avoids the false-negative that misses a posterior-fossa stroke.
Imaging in the dizzy patient is a triage tool, not a screening tool. Two questions decide it: is this an AVS with a central HINTS pattern, and is there a vascular red flag (new neurological symptoms, hearing loss, vascular risk factors)?
When the bedside exam is reassuringly peripheral and the case fits a known syndrome (BPPV, neuritis, migraine), imaging does not change management.
The most important fact about DWI-MRI in posterior-fossa stroke is its false-negative rate: roughly 12–20% in the first 24–48 hours for small infarcts.1A central HINTS pattern with a negative MRI still mandates admission and repeat imaging.2
CT angiography (CTA) of the neck and circle of Willis is the practical adjunct when vertebrobasilar disease is suspected — particularly useful for dissection.3Non-contrast CT remains essential before any thrombolysis decision, even though it poorly detects posterior-fossa ischaemia.4
The MRI-first principle applies whenever the HINTS battery flags central or indeterminate. CT is the bridge — it excludes haemorrhage before thrombolysis but cannot rule out ischaemia, especially in the posterior fossa. CTA earns its keep when dissection is suspected, when MRI is unavailable or contraindicated, or when the vessel anatomy will guide downstream decisions.
The vHIT / audiogram pairing belongs in this section even though they are not "imaging" in the strict sense. Together they discriminate peripheral from central and surface the AICA red flag at the bedside, often before the patient leaves the cubicle.
Modality matrix
For each modality: what it actually sees, when to order it, and the principal pitfall.
Acute intracranial haemorrhage. Late large infarcts.
Before any thrombolysis. Suspected haemorrhage.
Poor sensitivity for posterior-fossa ischaemia. Cannot exclude acute stroke.
Vertebrobasilar stenosis, dissection, occlusion.
Suspected vertebrobasilar TIA or AVS with central HINTS when MRI not immediate.
Contrast nephropathy risk. Vessel anatomy ≠ parenchymal infarction.
Acute infarction within minutes; brainstem and cerebellar lesions.
Suspected stroke, central HINTS pattern, persistent unexplained vertigo.
12–20% false-negative for small posterior-fossa infarct in the first 24–48 h.
Vertebrobasilar narrowing, occlusion, sometimes dissection.
Adjunct to MRI–DWI in suspected vertebrobasilar pathology.
Less sensitive than CTA for dissection; flow artefacts.
Canal-specific VOR gain reduction; sensorineural loss confirming AICA red flag.
All AVS where peripheral cause considered; all SSNHL-with-vertigo.
Operator-dependent; not a stroke exclusion test.
Decision rules in a hurry
- Central HINTS → activate stroke pathway → non-contrast CT → MRI–DWI.
- Peripheral HINTS, no hearing change → no imaging.
- Peripheral HINTS + acute hearing loss → MRI of IAC and posterior fossa to exclude AICA.
- Brief recurrent vertigo + vascular risk → MRI + CTA to evaluate TIA source.
- Classical positional vertigo on Dix-Hallpike → no imaging.