Imaging to Rule Out Cerebellar Stroke
For suspected acute cerebellar stroke, follow the ACR Appropriateness Criteria for Cerebrovascular Disease with immediate non-contrast CT head followed by CT angiography (CTA), though MRI with diffusion-weighted imaging (DWI) is the gold standard when available without treatment delay. 1, 2
Acute Presentation (Suspected Stroke)
First-Line Imaging Protocol
Non-contrast CT (NCCT) head should be obtained immediately to:
- Rule out hemorrhage, which is the primary exclusion criterion for thrombolytic therapy 2
- Provide rapid assessment (seconds to acquire) 2
- Detect early signs of infarction, though sensitivity is limited in the posterior fossa 1
However, CT has significant limitations for cerebellar stroke:
- CT is less sensitive and specific for posterior fossa pathology compared to MRI 1
- Subtle cerebellar findings (mild parenchymal atrophy, architectural distortion, or mild parenchymal changes) may not produce density differences significant enough for CT detection 1
- The posterior fossa location makes CT particularly challenging 1
Optimal Imaging: MRI with DWI
MRI with diffusion-weighted imaging (DWI) is the imaging modality of choice for diagnosing cerebellar infarction when it can be performed without delaying treatment 3, 4, 5:
- DWI detects ischemic changes within minutes with high sensitivity (98% detection rate) and specificity 4, 5
- DWI is considered the gold standard for ischemic core assessment 1
- MRI offers much better visualization of the posterior fossa compared to CT 1
- DWI is superior to conventional MRI sequences (T2-weighted, FLAIR) for early detection 4
MRI protocol should include:
- DWI sequences (primary diagnostic sequence) 2, 3, 4
- Apparent diffusion coefficient (ADC) maps to confirm restricted diffusion 4
- Gradient echo or susceptibility-weighted imaging to detect hemorrhage 1
- FLAIR sequences 4
- Consider MRA head and neck if vascular imaging needed 1, 2
Vascular Imaging
Add CTA head and neck (or MRA) for:
- Identifying large vessel occlusion requiring endovascular therapy 2
- Procedural planning if intervention is considered 1
- Assessing posterior circulation vasculature 1
The ACR guidelines specifically state that patients with suspected acute stroke should have imaging guided by the Cerebrovascular Disease criteria, not the ataxia protocols 1
Critical Timing Considerations
Within 6-hour window:
- NCCT followed by multiphase CTA is sufficient for treatment decisions 1
- CT perfusion (CTP) is not necessary for clinical decision-making in this timeframe 1
Beyond 6-hour window or unknown onset:
- Advanced imaging with perfusion assessment (CTP or MRI perfusion) becomes essential for treatment selection 1, 2
- This helps identify salvageable penumbra versus irreversible core 1, 2
Prognostic Value of Imaging
Quantitative volumetric assessment on DWI predicts outcome:
- Lesion volume on early DWI correlates significantly with clinical outcome 4, 6
- Lesion volume ≤22 mL predicts good outcome with 75% sensitivity and 100% specificity 4
- The ratio of lesion volume to whole cerebellar volume (rVolume) predicts poor outcome even when controlling for age and NIHSS 6
- Frank hypodensity on CT within first 6 hours and early midline shift predict cerebral edema 1
Important Caveats
DWI-negative cerebellar stroke can occur:
- Approximately 25.6% of stroke/TIA patients may have initial negative DWI 7
- Brainstem location and lacunar syndromes are more likely to be DWI-negative initially 7
- Follow-up imaging at 30 days may be needed if clinical suspicion remains high despite negative initial DWI 7
- Perfusion-weighted imaging may detect ischemia in some DWI-negative cases 7
Subacute cerebellar infarcts may be missed due to a "fogging" phenomenon on imaging 3
Never delay treatment for advanced imaging - the time-sensitive nature of reperfusion therapies must be balanced against obtaining comprehensive imaging 2
Do not rely solely on NCCT without vascular imaging as this may miss large vessel occlusions requiring endovascular therapy 2