Pulmonary Arteriovenous malformation

Related Subjects: |Pulmonary Embolism |Cardiogenic Pulmonary Oedema |Pulmonary Arteriovenous malformation

🫁 Pulmonary arteriovenous malformations (PAVMs) are abnormal direct connections between the pulmonary artery and pulmonary vein, creating a right-to-left shunt (blood bypasses the alveolar capillary bed). This causes hypoxaemia 😮‍💨 and, crucially, allows paradoxical emboli (clots/bacteria) to bypass the lung filter → stroke/TIA 🧠 and brain abscess 🧫. In the UK, most PAVMs are associated with Hereditary Haemorrhagic Telangiectasia (HHT) 👃🩸.

📖 About

• Definition: direct pulmonary artery–vein communication → high-flow vascular channel(s) (simple or complex).
• Key concept: right-to-left shunt → low PaO₂ and loss of pulmonary “filter”.
• Association: strongly linked with HHT (Osler–Weber–Rendu); can also be sporadic or rarely secondary.

🧬 Aetiology & Associations

• 👃🩸 HHT (most common): recurrent epistaxis, mucocutaneous telangiectasia, visceral AVMs (lung/liver/brain).
• Sporadic PAVM (no HHT features).
• Other (less common): congenital heart disease with right-to-left shunt physiology, prior thoracic surgery/trauma, hepatopulmonary syndrome (vascular dilatation rather than classic PAVM).

🔬 Pathophysiology

• Hypoxaemia 😮‍💨 from shunted blood that is not oxygenated in alveoli.
• Paradoxical embolisation 🧠: thrombus or septic emboli bypass capillary filtration → TIA/stroke or brain abscess.
• Polycythaemia 🩸 may occur as a compensatory response to chronic hypoxaemia.
• Haemorrhage risk 🩸: PAVMs can rupture → haemoptysis/haemothorax (risk increases in pregnancy).

🩺 Clinical Features

• Asymptomatic (common): incidental on imaging.
• Breathlessness 😮‍💨 and reduced exercise tolerance; may have platypnoea–orthodeoxia (worse upright).
• Hypoxaemia: low SpO₂ at rest or exertional desaturation.
• Cyanosis 🟦 and clubbing 👋 (especially in larger shunts).
• Haemoptysis 🩸 or pleuritic chest pain; rare catastrophic bleed (haemothorax).
• Neurological events 🧠: TIA/stroke, migraine, seizures.
• Infection complications 🧫: brain abscess (consider in fever/headache/focal neurology).

⚠️ Complications (high-yield)

• 🧠 Stroke/TIA from paradoxical emboli.
• 🧫 Brain abscess (septic emboli bypass pulmonary filter).
• 🩸 Haemoptysis / haemothorax (rupture).
• 🤰 Pregnancy: increased risk of enlargement/rupture and major haemorrhage → treat/assess pre-pregnancy where possible.

🔍 Investigations

• Bedside: SpO₂ (rest + exertion) 😮‍💨; examine for clubbing/cyanosis.
• 🩸 ABG if symptomatic/hypoxic (PaO₂ low; A–a gradient often raised).
• 🩻 CXR: may show rounded/serpiginous opacity with feeding vessel (can be normal).
• 🫧 Contrast echocardiography (bubble echo): screening test for right-to-left shunt (timing helps distinguish intracardiac vs intrapulmonary shunt).
• 🧲/🩻 CT pulmonary angiography (CTPA): defines anatomy (size, feeding artery diameter, number) and guides treatment planning.
• 🩸 Formal pulmonary angiography: usually performed as part of endovascular treatment planning/embolisation.
• 👃🩸 Assess for HHT: history of epistaxis, family history, mucocutaneous telangiectasia; consider genetics and screening for other AVMs (specialist pathways).

🧾 Types (anatomy)

• Simple PAVM (most common): single segmental feeding artery → single draining vein.
• Complex PAVM: multiple feeding arteries and/or draining veins.
• Diffuse PAVMs: multiple small lesions (harder to treat; significant shunt burden).

⚖️ Management (UK practice principles)

🎯 The key aim is to reduce right-to-left shunt and prevent stroke/brain abscess. Most treatable PAVMs are managed with transcatheter embolisation by interventional radiology. 🧵 Patients with suspected/confirmed HHT should be managed via specialist services where available. 👃🩸

• Endovascular embolisation (first-line) 🧵
  • Coils/plugs to occlude the feeding artery and PAVM sac.
  • Reduces hypoxaemia and lowers risk of paradoxical emboli.
  • Follow-up imaging is important (recanalisation/new PAVMs can occur, especially in HHT).
• Surgery 🔪
  • Rare now; considered if embolisation is not feasible or for life-threatening haemorrhage not controlled endovascularly.
• Medical/supportive 🫁
  • Oxygen if hypoxic; manage iron deficiency/polycythaemia appropriately.
  • Stroke prevention: focus on treating PAVM and standard vascular risk management (individualised).
• Preventing brain abscess / paradoxical emboli 🧠🧫
  • Give patients clear safety advice: seek urgent review for new focal neurology, severe headache, fever or seizure.
  • Many specialist pathways advise antibiotic prophylaxis for high-bacteraemia dental procedures in patients with untreated/residual PAVMs (local policy varies) and meticulous dental hygiene 🦷.
  • Use air filters and meticulous de-airing of IV lines (avoid air embolism) 💉⚠️.
• Pregnancy 🤰
  • Pre-pregnancy counselling and assessment is important; treat significant PAVMs before pregnancy where possible.
  • During pregnancy, manage in a specialist multidisciplinary team (respiratory + IR + obstetrics) due to haemorrhage risk.

📉 Prognosis

• Embolisation is usually effective, but lifelong follow-up may be required (especially with HHT) due to recurrence/new lesions.
• Untreated significant PAVMs carry a substantial long-term risk of neurological complications (TIA/stroke/brain abscess).

💡 Exam Pearls

• 🫁 PAVM = right-to-left shunt → hypoxaemia + stroke/brain abscess risk (loss of lung filter).
• 👃 Recurrent epistaxis + telangiectasia + PAVM = think HHT.
• 🫧 Bubble echo screens for shunt; CTPA defines anatomy; embolisation is first-line.

📖 References

• Radiopaedia: Pulmonary arteriovenous malformation
• NHS: Hereditary haemorrhagic telangiectasia (HHT)
• HHT UK (patient + specialist service information)