Module 13 · Disease pages

Central vHIT patterns

PICA, AICA, SCA strokes and the central mimics
Clinical vignette
A 67-year-old man with hypertension and atrial fibrillation arrives at the emergency department with two hours of severe spinning vertigo, nausea, and unsteadiness. He notes new hearing loss in his right ear. Bedside head impulse to the right is abnormal. There is right-beating spontaneous nystagmus that does not change direction on gaze. Test of skew is negative. The picture would fit vestibular neuritis except for the new unilateral hearing loss. MRI confirms a right-sided AICA-territory infarct.
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The central pseudoneuritis problem

The clinical importance of central vHIT patterns rests on a single fact: posterior-circulation stroke can mimic peripheral vestibular disease. A patient with an AICA-territory stroke damaging the labyrinthine artery may present with continuous vertigo, nausea, unilateral abnormal HIT, and ipsilateral hearing loss. The bedside picture and the vHIT can both fit vestibular neuritis. The cost of missing the diagnosis is high — posterior fossa stroke can evolve to malignant cerebellar swelling and is potentially treatable with intervention.

PICA, AICA, and the cerebellar mass effect

The three principal cerebellar arteries — PICA (posterior inferior cerebellar artery), AICA (anterior inferior cerebellar artery), and SCA (superior cerebellar artery) — supply different parts of the cerebellum and brainstem and produce distinguishable clinical syndromes when occluded:

  • PICA supplies the lateral medulla and the inferior cerebellum. Vertigo is common; vHIT is usually normal. Sometimes called the "most dangerous" vertiginous stroke because the bedside picture mimics a benign peripheral problem.
  • AICA supplies the lateral pons, the middle cerebellar peduncle, and — critically — the labyrinthine artery in 80% of people. AICA strokes can damage the labyrinth itself, producing peripheral-pattern vHIT plus hearing loss.
  • SCA supplies the upper cerebellum and is less often vertiginous; vHIT is usually normal.

Central pattern 1: PICA territory — normal vHIT, central oculomotor signs

Most PICA strokes leave the labyrinth and vestibular nerve intact. vHIT is normal. The diagnostic alarm is that the patient with continuous spontaneous vertigo has a normalhead impulse test — combined with central oculomotor signs (direction-changing nystagmus on gaze, skew deviation, or new gait ataxia disproportionate to vertigo). The HINTS examination was designed precisely for this scenario[Kattah JC 2009].

PICA-territory stroke — six-canal panel
0100200R latg=0.910100200L latg=0.930100200R antg=0.860100200L antg=0.870100200R postg=0.840100200L postg=0.83
vHIT is normal in classical PICA-territory stroke. The combination of continuous vertigo + normal vHIT + central oculomotor signs is the diagnostic pattern.

Central pattern 2: AICA territory — peripheral-pattern vHIT plus hearing loss

AICA strokes that involve the labyrinthine artery destroy the labyrinth, producing a peripheral-pattern vHIT identical to vestibular neuritis. The discriminator is unilateral hearing loss: vestibular neuritis spares hearing; AICA stroke usually does not. New unilateral hearing loss in a patient with acute vestibular syndrome and an abnormal HIT is AICA stroke until proven otherwise[Newman-Toker DE 2008].

AICA-territory stroke with labyrinthine ischaemia — right side
0100200R latg=0.380100200R antg=0.450100200R postg=0.50
Right-sided peripheral pattern indistinguishable from vestibular neuritis on the vHIT alone. The discriminator at the bedside is the audiogram and the rest of HINTS — not the vHIT.
2505001k2k4k8k020406080100120Frequency (Hz)Hearing level (dB HL)○ right× left
Sudden unilateral right-sided sensorineural hearing loss accompanying the acute vestibular syndrome — the audiogram is what separates AICA stroke from vestibular neuritis.

Central pattern 3: subtle, symmetric, and almost normal

A subset of central lesions, particularly involving the vestibular nuclei or flocculus, produce subtly low symmetric vHIT gains (often 0.60–0.80 bilaterally) with very small or absent corrective saccades[Chen L 2014]. The picture can resemble mild bilateral vestibulopathy but the saccadic pattern is wrong: in true peripheral bilateral loss, the brain generates corrective saccades because the eye lags target; in central reduction the corrective saccades may be inappropriate, late, or absent because the generator itself is impaired.

Wrong-way saccades

A rare but specific central sign: corrective saccades directed in the samedirection as the head movement, rather than the opposite. These "wrong-way saccades" reflect impaired central programming of the corrective response and are seen in cerebellar lesions. When present, they point firmly toward a central process.

Key teaching points

  • PICA strokes typically have normal vHIT; the alarm is normal HIT + continuous vertigo + central oculomotor signs.
  • AICA strokes can damage the labyrinthine artery and produce peripheral-pattern vHIT; the discriminator is new unilateral hearing loss.
  • HINTS-plus catches both: it asks "is the HIT normal?" (PICA) and "is there new hearing loss?" (AICA).
  • In vascular risk patients with vertigo, normal vHIT raises rather than lowers suspicion for posterior-circulation stroke.

References

  1. Newman-Toker DE, Kattah JC, Alvernia JE, Wang DZ. Normal head impulse test differentiates acute cerebellar strokes from vestibular neuritis. Neurology 2008;70:2378–85. doi:10.1212/01.wnl.0000314685.01433.0d
  2. Chen L, Todd M, Halmagyi GM, Aw S. Head impulse gain and saccade analysis in pontine-cerebellar stroke and vestibular neuritis. Neurology 2014;83:1513–22. doi:10.1212/WNL.0000000000000906
  3. Kattah JC, Talkad AV, Wang DZ, Hsieh YH, Newman-Toker DE. HINTS to diagnose stroke in the acute vestibular syndrome: three-step bedside oculomotor examination more sensitive than early MRI diffusion-weighted imaging. Stroke 2009;40:3504–10. doi:10.1161/STROKEAHA.109.551234
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