Can a chest CT (Computed Tomography) angiogram detect pulmonary arteriovenous malformations (PAVMs) in patients with suspected pulmonary AVMs, particularly those with hereditary hemorrhagic telangiectasia (HHT)?

Can Chest CT Angiogram Detect Pulmonary AVMs?

Yes, chest CT angiography (CTA) is highly effective at detecting pulmonary arteriovenous malformations (PAVMs) and accurately characterizes their number, size, location, and distribution for treatment planning. 1

Diagnostic Performance of CT Angiography

CTA chest with IV contrast offers high spatial resolution and can detect the number, size, and distribution of PAVMs accurately. 1 The American College of Radiology recommends CT chest with IV contrast as the preferred imaging modality for characterizing PAVMs once screening tests suggest their presence 2.

Key Advantages of CTA:

• Provides detailed anatomic information including PAVM location, feeding artery size, and draining vein anatomy that is essential for treatment planning 1
• Can detect PAVMs throughout all lung zones and characterize their distribution patterns (unique, multiple, disseminated, or diffuse) 3
• Allows measurement of feeding artery diameter, which correlates with risk of ischemic stroke (larger feeding arteries ≥4.9 mm associated with higher stroke risk) 3
• Enables counting of total PAVM burden, which correlates with brain abscess risk (higher numbers associated with increased risk) 3

Important Nuance: Contrast May Not Be Necessary

Interestingly, noncontrast CT chest provides similar diagnostic accuracy to contrast-enhanced CT due to the high natural contrast inherent to pulmonary anatomy. 1 Noncontrast CT can detect the number, size, and distribution of PAVMs accurately and predict PAVM angioarchitecture in 95% of cases using 3D reconstruction 1, 4.

Why This Matters:

• Avoiding IV contrast eliminates the small but real risk of air embolism in patients with confirmed PAVMs 4
• After positive screening with transthoracic contrast echocardiography (TTCE), proceed directly to CT chest WITHOUT IV contrast to confirm diagnosis and characterize PAVMs 4
• The term "CT angiogram" may be misleading in this context—standard chest CT (even without contrast) is sufficient for PAVM detection 1

Clinical Algorithm for PAVM Detection

Step 1: Initial Screening

• Use transthoracic contrast echocardiography (TTCE) with agitated saline as the first-line screening test with 97-99% sensitivity and 99% negative predictive value 4, 5
• Grade the shunt severity: Grade 0 (no bubbles), Grade 1 (<30 bubbles), Grade 2 (moderate filling), Grade 3 (complete left atrial opacification) 1, 4

Step 2: Confirmatory Imaging

• If TTCE is Grade 2 or 3, proceed to chest CT (preferably WITHOUT IV contrast) to confirm and characterize PAVMs 4
• CT will provide the anatomic detail needed: exact location, number of lesions, feeding artery size, and treatment planning information 1, 2

Step 3: Treatment Planning

• All PAVMs detected by CT should be considered for treatment regardless of feeding artery size due to paradoxical embolism risk 2, 6
• Digital subtraction angiography is typically performed at the time of embolization, not as a standalone diagnostic test 2

Common Pitfalls to Avoid

Don't Use CTA as Initial Screening

• CTA should not be the first test—it exposes patients to radiation and is more expensive than TTCE 4, 7
• TTCE has excellent sensitivity (97-99%) and can rule out PAVMs if negative, avoiding unnecessary CT scans 4, 5

Don't Rely on Chest X-ray Alone

• Chest radiography has only 60-70% sensitivity and will miss most PAVMs despite 98% specificity when classic findings are present 4

Remember Positional Testing

• Measure oxygen saturation in both supine and upright positions, as 65-83% of PAVMs are in lower lobes causing orthodeoxia (worse oxygenation when upright) 2, 4, 6

Surveillance After Treatment

Follow-up CT (without contrast preferred) is mandatory at 6-12 months after embolization, then every 3-5 years to detect persistence, recanalization, or new PAVMs 2, 4, 6. TTCE has low sensitivity for detecting recanalization after treatment, so CT is required for post-treatment surveillance 4.