When to Order a CTA
Order a CTA when you need to visualize arterial anatomy for suspected vascular pathology, with specific indications varying by anatomical territory and clinical presentation.
Coronary CTA (CCTA)
For suspected chronic coronary syndrome, CCTA is the first-line test when pre-test likelihood of obstructive coronary artery disease is between 5-50%. 1, 2
Clinical Decision Algorithm for Coronary Disease:
- Pre-test likelihood ≤5%: Defer further testing 2
- Pre-test likelihood 5-15%: Consider coronary artery calcium scoring first to reclassify patients 2
- Pre-test likelihood 5-50%: CCTA is the preferred initial diagnostic test 1, 2
- Pre-test likelihood 15-85%: Functional imaging (stress echo, SPECT, PET, or CMR) is preferred over CCTA 1, 2
- Pre-test likelihood >85%: Proceed directly to invasive coronary angiography 1, 2
Additional CCTA Indications:
- When functional imaging yields inconclusive results in patients with low-to-moderate pre-test likelihood 1, 2
- To diagnose coronary stenosis, atherosclerotic plaque, coronary dissection, or congenital anomalies 2, 3
- For treatment planning in multivessel disease when heart team decision-making is needed 4
CCTA Contraindications:
Do not order CCTA in patients with: 2
- Severe renal failure (eGFR <30 mL/min/1.73 m²)
- Decompensated heart failure
- Extensive coronary calcification
- Fast irregular heart rate
- Severe obesity
- Inability to cooperate with breath-hold commands
Cerebrovascular CTA
Head and Neck CTA for Acute Presentations:
Order CTA head and neck immediately when acute subarachnoid hemorrhage is detected on non-contrast CT to identify the bleeding source. 1 Ruptured cerebral aneurysm accounts for 70% of non-traumatic SAH, with 25% mortality after presentation. 1
In head trauma with suspected intracranial arterial injury, CTA head and neck is the standard initial test with sensitivity up to 100% and specificity of 100% for detecting blunt cerebrovascular injury. 1 This has replaced catheter angiography as first-line imaging due to faster acquisition and fewer safety concerns. 1
Specific Trauma Indications for CTA: 1
- Skull base fracture involving the carotid canal
- Abnormal enlargement of superior ophthalmic vein and cavernous sinus
- Unexplained neurologic deficit after trauma
- Epistaxis from suspected arterial source
- Penetrating head/neck trauma
- High-risk cervical or facial fractures
Pediatric Headache Indications:
Order CTA head and neck when acute stroke is suspected in children, though MRI/MRA is preferred when available. 1 CTA is indicated for suspected arterial dissection if MRA is inconclusive. 1
In children with sickle cell anemia presenting with acute headache, lower your threshold for CTA as they have higher risk for stroke, posterior reversible encephalopathy syndrome, and subarachnoid hemorrhage. 1
Abdominal Aortic CTA
Order CTA abdomen/pelvis when abdominal aortic aneurysm reaches 5.5 cm or becomes symptomatic to plan intervention (surgical vs. endovascular). 1 CTA is the optimal pre-intervention imaging modality. 1
For AAA surveillance <5.5 cm, ultrasound is preferred over CTA unless aneurysm morphology needs detailed characterization (e.g., saccular morphology in 4.0-5.5 cm aneurysms). 1
Peripheral Arterial CTA
Order lower extremity CTA in peripheral artery disease when planning revascularization to delineate the bilateral arterial tree and differentiate acute from chronic atherosclerotic changes. 5, 6
Critical Pitfalls to Avoid
Never order CTA in patients with severe renal impairment (eGFR <30 mL/min/1.73 m²) without considering alternative imaging. 2, 7 For GFR 30-45 mL/min/1.73 m², implement preventive measures including pre-procedural hydration with isotonic saline and minimizing contrast volume. 7
Do not order CCTA in very low-risk patients (≤5% pre-test likelihood) as this represents inappropriate overuse. 2
Avoid CCTA in high-risk patients (>50% pre-test likelihood) where functional imaging or direct invasive angiography is more appropriate. 2
Always ensure adequate hydration before and after CTA to minimize contrast-induced nephropathy risk. 3
In TIA patients without risk factors (no smoking history, no peripheral arterial disease, no prior stroke/TIA, normal ABCD2 score), CTA can be deferred in favor of ultrasound or MRI. 8 However, patients with these risk factors, male gender, hypertension, coronary disease, or shorter symptom duration warrant immediate CTA. 8