A 38-year-old woman presents with acute onset vertigo, nausea, and inability to walk in a straight line. Examination reveals positive Romberg test, dysmetria on finger-nose test, and horizontal nystagmus. CT brain is normal. What is the most appropriate investigation to identify acute cerebellar pathology?

Explanation

## Investigation of Choice for Acute Cerebellar Pathology ### Clinical Presentation Analysis **Key Point:** The acute onset of vertigo, nausea, positive Romberg test, dysmetria (finger-nose test), and nystagmus indicates acute cerebellar dysfunction. The normal CT brain does not exclude acute cerebellar stroke or other pathology because CT has low sensitivity for posterior fossa lesions. ### Why MRI with DWI is the Best Investigation **High-Yield:** MRI brain with diffusion-weighted imaging (DWI) is the gold standard for detecting acute ischemic stroke in the cerebellum. DWI sequences are highly sensitive for detecting restricted water diffusion within minutes of symptom onset, making them superior to conventional CT or standard MRI for acute cerebellar infarction. **Clinical Pearl:** Acute cerebellar stroke is a neurosurgical emergency because it can lead to obstructive hydrocephalus and brainstem compression. Early detection with MRI-DWI allows for timely intervention (decompressive surgery if needed) and thrombolytic therapy if within the therapeutic window. ### Investigation Comparison for Acute Cerebellar Pathology | Investigation | Sensitivity for Acute Cerebellar Stroke | Timing of Detection | Clinical Utility | |---|---|---|---| | MRI with DWI | Very high (>95%) | Minutes after onset | Gold standard; guides acute management | | CT brain | Low (especially posterior fossa) | Minutes | Excludes hemorrhage; misses ischemia | | EEG | Not useful for cerebellar pathology | Variable | Assesses cortical activity, not cerebellum | | Carotid Doppler | Not useful for cerebellar stroke | Variable | Assesses extracranial vessels, not cerebellar circulation | | Serum glucose/electrolytes | Not diagnostic for structural lesions | Minutes | Excludes metabolic causes of ataxia | **Key Point:** While CT is useful for excluding hemorrhage, it has poor sensitivity for acute ischemic lesions in the posterior fossa. MRI-DWI is far superior and is the standard of care for suspected acute cerebellar stroke. ### Diagnostic Algorithm for Acute Cerebellar Ataxia ```mermaid flowchart TD A[Acute cerebellar ataxia + vertigo + nystagmus]:::outcome --> B{CT brain normal?}:::decision B -->|Yes| C[Perform MRI with DWI urgently]:::action C --> D{Acute ischemic lesion?}:::decision D -->|Yes| E[Acute cerebellar stroke confirmed]:::outcome D -->|No| F[Consider other cerebellar pathology]:::action F --> G[Repeat MRI, assess for hemorrhage, tumor, or infection]:::action B -->|No - hemorrhage seen| H[Neurosurgical consultation]:::action ``` **Mnemonic:** **DWI-FAST** — **D**iffusion-**W**eighted **I**maging for **F**ast **A**cute **S**troke **T**riage in the cerebellum.