Thrombosis of posterior inferior cerebellar artery causes____

Explanation

## Correct Answer: A. Lateral medullary syndrome The **posterior inferior cerebellar artery (PICA)** is the terminal branch of the vertebral artery and supplies the lateral medulla, dorsolateral medullary region, and the inferior cerebellum. Thrombosis of PICA results in **Wallenberg syndrome** (lateral medullary syndrome), the most common brainstem stroke in clinical practice. The lateral medulla contains critical nuclei and tracts: the spinal trigeminal nucleus (causing ipsilateral facial pain/temperature loss), the spinothalamic tract (contralateral body pain/temperature loss), the nucleus ambiguus (ipsilateral vocal cord paralysis and dysphagia), the dorsal motor nucleus of vagus (ipsilateral palatal weakness), and sympathetic descending fibers (ipsilateral Horner syndrome). The medial lemniscus is spared because it lies in the medial medulla supplied by the vertebral artery proper. Clinically, patients present with the classic tetrad: ipsilateral facial anesthesia, contralateral body anesthesia, ipsilateral vocal cord paralysis with dysphagia, and ipsilateral Horner syndrome. This distinctive pattern of *crossed sensory loss* (ipsilateral face, contralateral body) is pathognomonic for lateral medullary syndrome and distinguishes it from other brainstem syndromes. PICA occlusion is the most common vascular cause, accounting for approximately 80% of Wallenberg syndrome cases in Indian stroke registries. ## Why the other options are wrong **B. Weber syndrome** — Weber syndrome results from **midbrain** infarction (typically from superior cerebellar artery or PCA occlusion), not PICA. It presents with ipsilateral oculomotor nerve palsy (CN III) and contralateral hemiparesis—a completely different anatomical level and vascular territory. This is a common NBE trap pairing brainstem syndromes without anatomical correlation. **C. Millard Gubler syndrome** — Millard Gubler syndrome occurs with **ventral pontine** infarction (from basilar artery branches), not PICA. It features ipsilateral facial weakness (CN VII) with contralateral hemiparesis. The pons is rostral to the medulla and has entirely different vascular supply and clinical presentation—students confuse it by grouping all brainstem syndromes together. **D. Medial medullary syndrome** — Medial medullary syndrome results from **medial medullary** infarction caused by vertebral artery occlusion (not PICA), affecting the medial lemniscus and hypoglossal nerve. It presents with ipsilateral tongue paralysis and contralateral body weakness—sparing facial sensation entirely. PICA supplies the *lateral* medulla, not medial structures. ## High-Yield Facts - **PICA occlusion** causes **Wallenberg (lateral medullary) syndrome**, the most common brainstem stroke in Indian stroke units. - **Crossed sensory loss** (ipsilateral face, contralateral body) is the discriminating sign of lateral medullary syndrome—no other brainstem syndrome has this pattern. - **Ipsilateral Horner syndrome** (miosis, ptosis, anhidrosis) occurs because sympathetic descending fibers in the lateral medulla are damaged. - **Nucleus ambiguus damage** causes ipsilateral vocal cord paralysis and dysphagia—patients have a 'nasal' voice and aspiration risk. - **Medial lemniscus is spared** in PICA stroke because it lies in the medial medulla supplied by the vertebral artery proper, not PICA. ## Mnemonics **PICA = Lateral Medulla = WATCH** **W**allenberg, **A**thetosis (cerebellar), **T**rigeminal (facial pain loss), **C**rossed sensory loss, **H**orner syndrome. All ipsilateral except crossed sensory loss. **Brainstem Stroke Levels** **MIDBRAIN** (Weber) = CN III palsy. **PONS** (Millard-Gubler) = CN VII palsy. **MEDULLA lateral** (Wallenberg/PICA) = CN V + IX + X + sympathetic. **MEDULLA medial** (vertebral artery) = CN XII palsy. ## NBE Trap NBE groups all brainstem syndromes together to trap students who memorize syndrome names without understanding vascular anatomy. The key discriminator is **PICA = lateral medulla only**; other arteries supply different medullary regions and produce different syndromes. ## Clinical Pearl In Indian stroke units, a patient presenting with acute dysphagia, hoarseness, and ipsilateral facial numbness with contralateral arm numbness should immediately raise suspicion for PICA stroke—early thrombolysis (within 4.5 hours per RNTCP guidelines) can prevent permanent disability. Aspiration precautions are critical because nucleus ambiguus involvement compromises airway protection. _Reference: Harrison Ch. 445 (Stroke); Robbins Ch. 28 (CNS vascular disease); Bailey & Love Ch. 60 (Neurosurgery)_