What artery is most likely affected in an old hypertensive man presenting with ataxia, ipsilateral facial sensory loss, dysphagia, Horner's (Horner syndrome) syndrome, and contralateral lower limb weakness?

Lateral Medullary Syndrome: PICA Territory Infarction

The posterior inferior cerebellar artery (PICA) is the most likely affected vessel in this clinical presentation, representing classic lateral medullary syndrome (Wallenberg syndrome). 1

Clinical Syndrome Analysis

This patient's constellation of symptoms represents the classic lateral medullary syndrome:

• Ipsilateral findings: Ataxia, facial sensory loss, dysphagia, and Horner's syndrome are all characteristic of lateral medullary involvement 1, 2
• Contralateral findings: The contralateral lower limb weakness (though atypical) can occur with involvement of descending corticospinal fibers in the lateral medulla 3
• Vascular territory: PICA typically arises from the vertebral artery and supplies the lateral medulla and inferior cerebellum 1

Why PICA and Not the Other Options

PICA (Option A) is correct because:

• The vertebrobasilar system, which includes PICA, commonly presents with ataxia, cranial nerve deficits, dizziness, and incoordination 1
• Dysphagia is a recognized manifestation of lateral medullary infarction due to involvement of the nucleus ambiguus 2
• Horner's syndrome results from disruption of descending sympathetic fibers in the lateral medulla 2, 4

AICA (Option B) is incorrect because:

• AICA territory infarcts present with vertigo, tinnitus, facial weakness, lateral gaze palsy, and hearing loss 5
• The clinical features emphasize pontine involvement and lateral pontine syndrome rather than medullary findings 5
• Dysphagia is not a prominent feature of AICA territory strokes 5

Anterior cerebellar artery (Option C) is not a recognized major cerebellar artery—this is likely referring to superior cerebellar artery (SCA), which would present with prominent dysarthria and ataxia but without the characteristic medullary signs like Horner's syndrome or dysphagia 6

Basilar artery (Option D) is incorrect because:

• Basilar artery occlusion produces bilateral findings, altered consciousness, and involvement of multiple posterior circulation territories 1
• This patient has a focal, unilateral lateral medullary presentation inconsistent with basilar occlusion 1

Key Clinical Pitfall

Contralateral motor weakness is uncommon but can occur in lateral medullary syndrome when the lesion extends to involve ipsilateral corticospinal fibers caudal to the pyramidal decussation or causes compression of the decussation 3. This atypical finding should not distract from the otherwise classic PICA territory presentation.

Underlying Etiology in This Patient

Given the patient's profile (elderly, hypertensive):

• Large-artery atherosclerotic disease in the vertebrobasilar system is the most common cause, particularly affecting the distal vertebral or proximal basilar artery 5
• The vertebral artery origin or intracranial vertebral artery stenosis are typical culprit lesions 7, 5