What should be looked for on a Computed Tomography Angiography (CTA) scan?

What to Look for on CTA

When evaluating a Computed Tomography Angiography (CTA) scan, physicians should systematically assess for vascular abnormalities including stenoses, occlusions, aneurysms, arteriovenous malformations, and signs of active bleeding. 1

Key Elements to Evaluate on CTA

Vascular Anatomy and Pathology

• Vessel occlusions:

  • CTA has 92-100% sensitivity and 82-100% specificity for detecting intracranial occlusions 1
  • Assess for hyperdense vessel signs (e.g., hyperdense MCA sign)
  • Evaluate clot length and burden which relates to recanalization success 1

• Vessel stenoses:

  • Look for narrowing of vessel lumen
  • Quantify degree of stenosis (mild: 10-29%, moderate: 30-69%, severe: 70-99%) 2
  • CTA has 97.1% sensitivity and 99.5% specificity for detecting ≥50% stenosis 3

• Aneurysms:

  • Evaluate size, location, neck width, and relationship to parent vessels
  • Identify mural calcification and thrombus which impact treatment decisions 1
  • CTA has 96.3% sensitivity and 100% specificity for aneurysm detection with modern scanners 1
  • Note: sensitivity decreases to 81.8% for aneurysms <3mm 1

• Arteriovenous malformations (AVMs):

  • Assess nidus size, feeding arteries, and draining veins
  • Evaluate for high vs. low flow characteristics
  • Identify dural/transosseous feeding, venous narrowing, and venous pouches 4

Beyond Vascular Findings

• Parenchymal assessment:

  • CTA source images (CTA-SI) provide information about cerebral blood volume
  • For early strokes (<3 hours), CTA-SI has greater sensitivity to ischemic changes than non-contrast CT 1
  • Evaluate for hemorrhage, mass effect, and hydrocephalus 1

• Collateral circulation:

  • Assess presence and extent of collateral vessels, especially important in ischemic stroke 1
  • CTA can visualize collaterals and arteries distal to occlusions that may not appear on conventional angiography 1

Technical Considerations

• Image quality factors:

  • Timing of contrast bolus is critical for optimal arterial opacification
  • Evaluate for motion artifacts which can degrade image quality
  • Be aware of limitations in heavily calcified vessels, particularly in tibial arteries 1

• Reconstruction techniques:

  • Review multiplanar reformats (axial, coronal, sagittal)
  • Assess maximum intensity projections (MIPs) for overview of vascular anatomy
  • Volume-rendered images help with 3D spatial relationships 1

Limitations to Consider

• Potential pitfalls:
  • CTA provides static images of vascular anatomy and lacks flow dynamics information (consider 4D-CTA for flow assessment) 5
  • Heavily calcified atherosclerotic disease can limit interpretation, especially in older, diabetic, or dialysis patients 1
  • Metal artifacts from clips, coils, or stents may degrade image quality 1
  • Small vessel visualization (<3mm) may be limited compared to DSA 1

CTA offers excellent visualization of vascular anatomy with high sensitivity and specificity for most vascular pathologies, while providing additional cross-sectional information about surrounding structures that conventional angiography cannot provide.