What type of computed tomography (CT) scan is needed for a patient presenting with a Transient Ischemic Attack (TIA) and likely history of cardiovascular disease?

CT Imaging for TIA: Initial Evaluation

For a patient presenting with TIA, start with a noncontrast CT head to exclude hemorrhage and stroke mimics, then immediately add CTA of the head and neck to evaluate for treatable vascular lesions—this combined approach should be completed within 48 hours and ideally within 12 hours of presentation. 1, 2

Essential Initial Imaging: Noncontrast CT Head

Noncontrast CT of the head without IV contrast is the mandatory first imaging study for all TIA patients. 1, 3 This serves several critical functions:

• Excludes intracranial hemorrhage, which is an absolute contraindication to thrombolytics, anticoagulants, and antiplatelet agents used to prevent subsequent stroke 1
• Rules out stroke mimics including intracranial masses, infections, and other lesions that can present identically to TIA 1
• Identifies early ischemic changes that correlate with risk of subsequent stroke, regardless of chronicity 1
• Provides prognostic information: patients with new infarcts on CT have a 4-fold increased risk of subsequent stroke (OR 4.06) 4

Critical Caveat

Never use CT head with IV contrast alone—it has no role in TIA evaluation and may actually obscure hemorrhage. 1, 3 The American College of Radiology explicitly states there is no relevant literature supporting contrast-enhanced CT without a preceding noncontrast study. 1

Add Vascular Imaging: CTA Head and Neck

After obtaining noncontrast CT, immediately proceed to CTA of both the head and neck with IV contrast in the same imaging session. 1, 2 This is particularly critical because:

• CTA neck rapidly evaluates extracranial carotid disease, which is essential since the 90-day risk of ipsilateral stroke after carotid territory TIA is 20.1% 1, 2
• American Heart Association guidelines mandate noninvasive carotid imaging within 48 hours for TIA patients who are candidates for carotid endarterectomy or stenting 1, 2
• CTA head identifies intracranial atherosclerosis and steno-occlusive disease that may guide treatment decisions 1
• Combined CT/CTA provides the most rapid and cost-effective evaluation at approximately $1,460 per patient compared to $2,090 for CT followed by MRI 5

Important Limitation

Heavy calcifications can lead to overestimation of stenosis on CTA neck, so be aware of this potential pitfall when interpreting results. 1

Timing Is Critical

Complete imaging within 12 hours of presentation when possible, and absolutely within 48 hours. 2 The urgency is driven by stroke risk:

• 8.8% risk of stroke at 7 days after TIA 1, 2
• 11.6% risk at 90 days 1, 2
• 20.1% risk at 90 days for symptomatic carotid disease 1, 2

Delaying imaging beyond 48 hours substantially increases the risk of missing the window for preventive interventions. 2

Alternative: MRI/MRA (When CT/CTA Is Insufficient)

MRI with MRA is superior to CT for detecting small ischemic lesions (39% vs 8% detection rate in TIA, 86% vs 18% in minor stroke), but should be reserved for specific scenarios rather than routine initial evaluation 6:

• Renal impairment or contrast allergy preventing CTA 1
• Repeat TIA presentations where radiation exposure is a concern 1
• When CT/CTA is negative but clinical suspicion remains high 6

Time-of-flight MRA without contrast is sufficiently sensitive to screen for intracranial lesions and can be performed within 24-48 hours if not done in the emergency department. 1, 2

What NOT to Order

Avoid these studies in routine TIA evaluation:

• CT perfusion: Not typically used for initial TIA assessment; may identify abnormalities in one-third of cases but doesn't improve outcomes 1
• CT or MR venography: No role unless cerebral venous thrombosis is specifically suspected 1
• Catheter angiography: Too invasive for initial evaluation; reserve for secondary workup if endovascular therapy is being considered 1

Practical Algorithm

1. Immediate noncontrast CT head (within 12 hours of presentation) 1, 2, 3
2. Add CTA head and neck in the same session if no contraindications 1, 2
3. If contrast contraindicated: Obtain MRI/MRA within 24-48 hours 1, 2
4. If initial imaging negative but high clinical suspicion: Consider MRI with diffusion-weighted imaging to detect small infarcts 6