A 68-year-old woman from Delhi presents with acute onset of vertigo, nausea, and vomiting following a sudden severe headache. On examination, she has nystagmus (fast phase to the left), truncal ataxia, and inability to stand without support. Cranial nerve examination is normal. MRI shows an acute infarct in the right superior cerebellar artery (SCA) territory affecting the cerebellar vermis and right hemisphere. Which of the following cerebellar nuclei is most critically affected in this infarction, explaining her truncal ataxia and vertigo?

Explanation

## Clinical Presentation Analysis This patient presents with **acute cerebellar syndrome** characterized by: - **Truncal ataxia** (inability to sit/stand without support) - **Vertigo and nystagmus** (vestibular signs) - **Nausea and vomiting** (brainstem/vestibular involvement) - **Normal cranial nerves** (rules out brainstem stroke) - **Vermis and right hemisphere involvement** (SCA territory) ## Cerebellar Nuclei Anatomy and Function **Key Point:** The cerebellum has four pairs of nuclei (from medial to lateral): | Nucleus | Location | Function | Output | |---------|----------|----------|--------| | **Fastigial** | Medial (vermis) | Balance, posture, truncal control | Vestibular nuclei, reticular formation | | **Interposed** | Intermediate | Limb coordination | Red nucleus | | **Dentate** | Lateral | Fine motor planning | Thalamus (VL) | | **Vestibular** | Not a cerebellar nucleus | Vestibular input/output | Brainstem | ## Why Fastigial Nucleus Lesion Explains This Case **High-Yield:** The **fastigial nucleus receives input from the vermis** (midline cerebellar cortex) and projects to: 1. **Vestibular nuclei** → controls balance and eye movements 2. **Reticular formation** → controls posture and truncal muscles Damage to the fastigial nucleus → loss of vestibular and postural control → **truncal ataxia + vertigo + nystagmus**. **Clinical Pearl:** Remember the **medial-to-lateral rule**: - **Medial (vermis + fastigial)** → balance & posture (truncal ataxia if damaged) - **Lateral (hemisphere + dentate)** → limb coordination (dysmetria if damaged) This patient has **truncal ataxia without limb dysmetria**, pointing to **vermis/fastigial involvement**, not lateral cerebellar hemisphere. ## SCA Territory Infarction The superior cerebellar artery supplies: - Dentate nucleus (lateral) - Interposed nuclei (intermediate) - **Fastigial nucleus (medial)** ← most relevant here - Superior cerebellar peduncle - Cerebellar cortex Although all three nuclei are in the SCA territory, the **fastigial nucleus** is the key structure explaining the **truncal ataxia and vestibular signs** (vertigo, nystagmus). **Mnemonic:** **FAVE** = **F**astigial → **A**xial/**V**estibular/**E**quilibrium (balance) [cite:Snell's Clinical Neuroanatomy 8e Ch 7]