A 58-year-old man with hypertension and atrial fibrillation presents with acute onset vertigo, nystagmus, and truncal ataxia. MRI DWI shows restricted diffusion in the territory marked **A** in the diagram. On examination, the head impulse test is normal, but he has direction-changing nystagmus and a positive test of skew. Which of the following is the most likely vascular territory involved?
A. Basilar artery perforators supplying the midline pons and midbrain
B. Superior cerebellar artery (SCA) supplying the superior cerebellar hemisphere and dentate nucleus
C. Anterior inferior cerebellar artery (AICA) supplying the flocculus and ventral pons
D. Posterior inferior cerebellar artery (PICA) supplying the inferior cerebellar hemisphere and vermis
Explanation
Why "Posterior inferior cerebellar artery (PICA) supplying the inferior cerebellar hemisphere and vermis" is right
The clinical presentation of acute vertigo, nystagmus, truncal ataxia, and a normal head impulse test with direction-changing nystagmus and positive skew test is pathognomonic for isolated cerebellar infarction in the PICA territory. The HINTS examination (Head Impulse normal, Nystagmus direction-changing/vertical, Test of Skew positive) reliably distinguishes central from peripheral vestibular causes. PICA accounts for approximately 40% of cerebellar infarcts and supplies the inferior cerebellar hemisphere and vermis, producing this exact clinical syndrome. The MRI DWI restricted diffusion in the territory marked A confirms acute ischemia in the PICA distribution. According to AHA/ASA Stroke Guidelines 2024, PICA stroke is most commonly due to large-artery atherosclerosis of the vertebral artery or cardioembolism (as in this patient with atrial fibrillation).
Why each distractor is wrong
Superior cerebellar artery (SCA) supplying the superior cerebellar hemisphere and dentate nucleus: SCA infarcts present with dysarthria, ataxia, and tremor but typically spare the vermis and inferior hemisphere. Patients with SCA territory infarcts do not classically present with the isolated truncal ataxia and direction-changing nystagmus pattern seen here.
Anterior inferior cerebellar artery (AICA) supplying the flocculus and ventral pons: AICA territory infarcts produce facial pain/temperature loss, hearing loss, and facial weakness (facial nerve nucleus involvement), which are not present in this patient. AICA does not supply the inferior vermis.
Basilar artery perforators supplying the midline pons and midbrain: Basilar perforator infarcts cause locked-in syndrome, vertical gaze palsy, or pontine signs (bilateral weakness, hyperreflexia), not isolated cerebellar ataxia and nystagmus.
High-YieldNEET PG
PICA territory infarction presents with isolated cerebellar signs (normal head impulse test, direction-changing nystagmus, truncal ataxia) and accounts for ~40% of cerebellar strokes; HINTS exam distinguishes it from peripheral vestibular disease.
AHA/ASA Stroke Guidelines 2024; Wallenberg Syndrome and PICA Territory Infarction
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