What is the best way to screen for a pulmonary arteriovenous malformation (AVM)?

Screening for Pulmonary Arteriovenous Malformations

Initial Screening Test

Transthoracic contrast echocardiography (TTCE) with agitated saline is the recommended initial screening test for pulmonary arteriovenous malformations, with a sensitivity of 97-99% and negative predictive value of 99%. 1, 2

How TTCE Works

• Agitated saline microbubbles are injected intravenously and visualized appearing in the left atrium after 3-8 cardiac cycles following initial right heart opacification, indicating an intrapulmonary shunt 1
• A semiquantitative grading system is used: Grade 0 (no bubbles), Grade 1 (<30 bubbles), Grade 2 (moderate filling), Grade 3 (complete left atrial opacification) 1
• Grades 2 and 3 correlate strongly with larger shunts and increased risk of cerebral complications, with Grade 3 having a positive predictive value of 0.87 for requiring treatment 1
• Adverse events including air embolism occur in <1% of cases 1

Key Advantage Over Alternative Screening

• TTCE detects PAVMs that would be missed by chest radiography (sensitivity only 60-70%) or arterial blood gas shunt studies alone 1, 2
• In one prospective study, TTCE was the only positive screening test in 31% of patients with PAVMs who would have otherwise gone undiagnosed 3

Confirmatory Imaging After Positive Screening

If TTCE is positive (Grade 2 or 3), proceed directly to CT chest without IV contrast to confirm the diagnosis and characterize the PAVMs for treatment planning. 1

Why CT Without Contrast is Preferred

• Noncontrast CT offers high spatial resolution and accurately detects the number, size, location, and distribution of PAVMs 1
• The high natural contrast inherent to pulmonary anatomy makes IV contrast unnecessary for PAVM diagnosis 1
• Avoiding IV contrast eliminates the small but real risk of air embolism in patients with confirmed PAVMs 1
• 3D reconstruction from noncontrast CT can predict PAVM angioarchitecture in 95% of cases 1

When to Consider Contrast-Enhanced CT

• CTPA (CT pulmonary angiography with IV contrast) may be used if you need to correlate PAVM grade with echocardiography findings more sensitively than noncontrast CT 1
• CTA chest (contrast timed for aorta) is specifically useful if you suspect systemic arterial supply to the PAVM, which can occur and requires identification for treatment planning 1, 4
• Critical precaution: If using any IV contrast in a patient with suspected or confirmed PAVM, take meticulous care to prevent air embolism during IV line setup and contrast administration 1, 5

Alternative Confirmatory Imaging

Contrast-enhanced MRA of the pulmonary arteries can be used as an alternative to CT in children and young adults to avoid radiation exposure, with 92-93% sensitivity for detecting PAVMs with feeding arteries ≥2 mm. 1, 6

• MRA has excellent negative predictive value (99-100%) for clinically significant PAVMs 6
• The main limitation is a higher false-positive rate (specificity 62-97% depending on reader experience) compared to CT 1, 6
• MRA detected more small PAVMs (<5 mm) than conventional angiography in one study, though the clinical significance of these tiny lesions is uncertain 1, 7

What NOT to Use for Screening

• Chest radiography alone: Too insensitive (60-70% sensitivity) and will miss most PAVMs despite 98% specificity when classic findings are present 1
• Transesophageal echocardiography (TEE): No role as a standalone screening tool; only useful to rule out intracardiac shunts 1
• MRA without contrast: No role in PAVM screening 1
• Pertechnetate albumin pulmonary scan: Obsolete technique with no role in modern practice 1

Special Screening Considerations

High-Risk Populations Requiring Screening

• 70-90% of PAVM patients have hereditary hemorrhagic telangiectasia (HHT), an autosomal dominant disorder 8
• Screen all patients with HHT or first-degree relatives of HHT patients for PAVMs using TTCE 8, 7
• Look for recurrent epistaxis, mucocutaneous telangiectasias, family history of HHT, and other visceral involvement 8

Positional Oxygen Saturation Testing

• Measure oxygen saturation in both supine and upright positions, as 65-83% of PAVMs are in the lower lobes causing orthodeoxia (worse oxygenation when upright) and platypnea 8
• Standard single-position pulse oximetry may miss this important clinical clue 8

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 8
• TTCE has low sensitivity for detecting recanalization after treatment, so CT is required for post-treatment surveillance 1