What CT (Computed Tomography) scan, with or without contrast, is used to rule out stroke?

CT Imaging to Rule Out Stroke

Noncontrast CT head (without IV contrast) is the essential initial imaging study to rule out stroke, specifically to exclude intracranial hemorrhage and identify early ischemic changes before initiating treatment. 1

Initial Imaging: Noncontrast CT Head

The noncontrast CT head is the cornerstone of acute stroke evaluation and must be obtained first. 1, 2 This study serves multiple critical functions:

• Excludes intracranial hemorrhage (ICH), which is absolutely essential before administering IV thrombolytic therapy or initiating endovascular thrombectomy (EVT). 1
• Identifies early ischemic changes that help estimate the extent of irreversible tissue damage and guide therapeutic decisions using scoring systems like ASPECTS (Alberta Stroke Program Early Computed Tomography Score). 1
• Rules out stroke mimics and other potential etiologies for neurological symptoms. 1, 2
• Provides rapid diagnosis with widespread availability, making it the ideal first study in time-sensitive stroke care. 3

Role of Contrast CT Studies

CT head with IV contrast alone has NO role in acute stroke evaluation. 1 The American College of Radiology guidelines explicitly state there is no relevant literature supporting the use of contrast-enhanced CT of the head in evaluating ischemic stroke. 1

Similarly, CT head without and with IV contrast is NOT appropriate for stroke evaluation, as there is no supporting literature for this approach. 1

Critical Pitfall to Avoid

Contrast administration may actually obscure early complications such as hemorrhage, making it counterproductive in acute stroke imaging. 1

When to Add CTA (With Contrast)

After obtaining the initial noncontrast CT head, CTA head with IV contrast should be added immediately if large vessel occlusion (LVO) is suspected. 1

• CTA head is the most rapid means of detecting intracranial large vessel occlusions with high sensitivity and specificity. 1
• CTA is supported by multiple randomized controlled trials as the preferred method for LVO detection due to the time-sensitive nature of stroke care. 1
• CTA neck can be rapidly acquired together with CTA head to evaluate extracranial vasculature and assist with endovascular surgical planning. 1

Timing Considerations

Within the first 6 hours of symptom onset, CT perfusion is usually not necessary as an initial examination. 1 In fact, delays created by obtaining and analyzing CT perfusion in clear EVT candidates may be harmful. 1

For presentations 6-24 hours after onset, CT perfusion with IV contrast may be required to determine EVT eligibility in anterior circulation strokes with confirmed LVO. 1

Clinical Algorithm

1. Start with noncontrast CT head in all suspected stroke patients 1, 2
2. If hemorrhage is excluded and LVO is suspected, immediately proceed to CTA head (and neck if appropriate) 1
3. For presentations beyond 6 hours with confirmed LVO, consider adding CT perfusion to determine EVT eligibility 1
4. Never use contrast-enhanced CT alone or CT with and without contrast for stroke evaluation 1