Pulmonary Arteriovenous Malformation

Risk factors

• Hereditary hemorrhagic telangiectasia (autosomal dominant; mutations in ENG, ACVRL1, SMAD4)
• Prior chest trauma or surgery
• Chronic liver disease (hepatopulmonary syndrome — functionally distinct shunting, not true AVM)
• Schistosomiasis, actinomycosis, metastatic cancer (acquired causes)
• Fontan circulation (post-Glenn shunt) — develop arteriovenous malformations in the lung receiving the hepatic-factor-deficient venous return

Pathophysiology

True AVMs are typically congenital; abnormal mesodermal differentiation produces a sac-like or diffuse vascular channel connecting an enlarged feeding pulmonary artery directly to a draining pulmonary vein. Blood bypasses the alveolar gas exchange surface, producing hypoxemia that does not correct fully with supplemental oxygen (right-to-left shunt physiology, shunt fraction often >5%). The capillary filter is lost, so paradoxical emboli (thrombi, septic emboli, air) cross from the venous to the systemic circulation producing stroke and brain abscess.

Clinical presentation

Differential diagnosis

• Solitary pulmonary nodule (other etiology) — Lacks feeding artery and draining vein on contrast CT; manage per Fleischner
• Pulmonary varix — Dilated pulmonary vein without arterial connection; benign, often incidental
• Bronchogenic cyst — Fluid-filled, no enhancement, no vascular connection
• Hepatopulmonary syndrome — Cirrhosis with platypnea-orthodeoxia and intrapulmonary vascular dilatation on contrast echo; diffuse rather than focal
• Right-to-left intracardiac shunt — Patent foramen ovale, ASD — bubble study shows immediate (within 3 cardiac cycles) contrast in left heart; delayed appearance (3-8 cycles) suggests pulmonary shunt
• Pulmonary metastasis — Known primary, smooth nodule without feeding vessel

Diagnostic workup

Diagnostic algorithm

flowchart TD
  A[Suspected PAVM<br/>or HHT screening] --> B[Bubble echo<br/>agitated saline]
  B --> C{Delayed bubbles<br/>3-8 cycles?}
  C -->|Yes| D[Contrast chest CT]
  C -->|No| E[Low probability<br/>recheck if symptoms]
  D --> F{Feeding artery<br/>>=2-3 mm?}
  F -->|Yes| G[Transcatheter coil<br/>or plug embolization]
  F -->|No| H[Surveillance<br/>q3-5 years]
  G --> I[Lifelong abx prophylaxis<br/>+ Brain MRI<br/>+ HHT genetic testing]
  H --> I

Treatment

Complications

• Paradoxical embolic stroke, transient ischemic attack
• Brain abscess from septic emboli — neurologic deficit + fever in HHT patient is brain abscess until proven otherwise
• Massive hemoptysis or hemothorax, particularly during pregnancy
• Chronic hypoxemia and secondary polycythemia
• Migraine with aura associated with right-to-left shunt

PANCE pearls

• PaO2 that fails to rise normally on 100% O2 indicates a true shunt — pulmonary AVM, intracardiac shunt, or hepatopulmonary syndrome.
• Delayed appearance of bubbles in the left atrium (3-8 cycles after right atrial opacification) on contrast echo distinguishes pulmonary shunt from intracardiac shunt (within 3 cycles).
• All patients with PAVM need lifelong antibiotic prophylaxis before invasive procedures because the lost capillary filter allows transient bacteremia to reach the brain.
• Curacao criteria diagnose HHT clinically — three or four features = definite. Genetic testing confirms but is not required.
• Embolization is the first-line therapy — surgery is reserved for failure or massive hemoptysis.

References

• International HHT 2020 — Faughnan ME et al. Second International Guidelines for the Diagnosis and Management of Hereditary Hemorrhagic Telangiectasia. Ann Intern Med 2020;173:989-1001
• ATS / CHEST — Shovlin CL. Pulmonary Arteriovenous Malformations. AJRCCM 2014;190:1217-1228
• Curacao Criteria — Shovlin CL et al. Diagnostic Criteria for Hereditary Hemorrhagic Telangiectasia (Rendu-Osler-Weber Syndrome). Am J Med Genet 2000;91:66-67