## Lateral Medullary Syndrome (Wallenberg Syndrome) **Key Point:** Lateral medullary syndrome is classically caused by occlusion of the **posterior inferior cerebellar artery (PICA)**, which is the most common vascular supply to the lateral medulla. ### Vascular Supply to the Medulla | Artery | Territory | Syndrome | | --- | --- | --- | | **PICA** | Lateral medulla (dorsolateral) | Wallenberg (lateral medullary) | | AICA | Ventrolateral pons | Foville syndrome | | SCA | Dorsal midbrain/pons | Weber syndrome | | Basilar perforators | Medial medulla | Medial medullary syndrome | **High-Yield:** PICA arises from the **vertebral artery** and supplies the lateral medulla, inferior cerebellar peduncle, and choroid plexus of the fourth ventricle. Occlusion of PICA is responsible for >90% of lateral medullary infarcts. ### Classic Wallenberg Triad 1. **Ipsilateral facial pain/numbness** — trigeminal nucleus involvement 2. **Contralateral body pain/temperature loss** — spinothalamic tract crossing 3. **Ipsilateral Horner syndrome** — sympathetic fibers in dorsolateral medulla **Clinical Pearl:** The crossed sensory loss (ipsilateral face, contralateral body) is pathognomonic for lateral medullary syndrome and helps localize the lesion to the dorsolateral medulla where the trigeminal nucleus sits above the crossing spinothalamic tract. **Mnemonic:** **PICA = Posterior Inferior Cerebellar Artery** — the most common culprit in Wallenberg syndrome. Remember: PICA from Vertebral artery → lateral medulla → Wallenberg. ### Why PICA is Most Common - PICA is a terminal branch of the vertebral artery and has a long course along the lateral medulla - Atherosclerotic plaques in the vertebral artery frequently lodge at the PICA origin - Vertebral artery dissection (common in hypertension and trauma) often extends to occlude PICA - Accounts for approximately 75–90% of all lateral medullary infarcts
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