Lateral Medullary Syndrome: PICA Territory Infarction
The posterior inferior cerebellar artery (PICA) is the most likely affected vessel in this patient presenting with classic lateral medullary (Wallenberg) syndrome. 1
Clinical Syndrome Recognition
This patient demonstrates the pathognomonic constellation of lateral medullary syndrome:
- Ipsilateral findings: Facial sensory loss, Horner's syndrome, and ataxia 1, 2
- Contralateral findings: Body pain/temperature loss (manifesting as lower limb weakness in the question) 2
- Midline brainstem findings: Dysphagia from nucleus ambiguus involvement 3
The triad of Horner's syndrome (91% of cases), ipsilateral ataxia (85%), and contralateral hypalgesia (85%) clinically identifies lateral medullary infarction with high specificity 4.
Vascular Anatomy and Territory
PICA typically arises from the vertebral artery and supplies the lateral medulla and inferior cerebellum 1. The lateral medullary arteries, averaging 0.31 mm in diameter, usually originate from the vertebral artery and PICA, supplying precisely this lateral medullary region 5.
In a large series of 130 consecutive patients with pure lateral medullary infarction, vertebral artery disease was confirmed in 67% and isolated PICA disease in 10% 3. The American Heart Association confirms that the vertebrobasilar system, which includes PICA, commonly presents with ataxia, cranial nerve deficits, dizziness, and incoordination 1.
Why Not the Other Arteries?
AICA (Option B): Supplies the lateral pons and middle cerebellar peduncle, producing facial nerve palsy, hearing loss, and lateral pontine syndrome—not lateral medullary syndrome 5
Anterior cerebellar artery (Option C): This is not a recognized major cerebellar artery; the three cerebellar arteries are PICA, AICA, and superior cerebellar artery 5
Basilar artery (Option D): Occlusion produces bilateral findings, altered consciousness, and involvement of multiple posterior circulation territories rather than this focal unilateral lateral medullary presentation 1
Risk Factors and Pathophysiology
In elderly hypertensive patients, large-artery atherosclerotic disease in the vertebrobasilar system is the most common cause, particularly affecting the distal vertebral or proximal basilar artery 1. The vertebral artery origin or intracranial vertebral artery stenosis represents the typical culprit lesion 1.
Vertebral artery dissection should also be considered, as it may present with Horner syndrome, headache, or neck pain 6. However, in this elderly hypertensive patient, atherosclerotic disease is more likely 1.
Clinical Pitfall
The presence of contralateral "weakness" in the question likely represents sensory loss (hypalgesia/temperature loss) rather than true motor weakness, as the corticospinal tract runs medially in the medulla and is typically spared in lateral medullary syndrome 2, 3. True contralateral motor weakness would suggest medial medullary involvement from anterior spinal artery territory infarction, not PICA 5.