What is a pulmonary AVM?
Normally, blood pumped from the heart to the lungs passes through a fine network of capillaries, where it picks up oxygen and where small clots and bacteria are filtered out. A pulmonary arteriovenous malformation (AVM) is an abnormal, direct connection between a lung artery and a lung vein that bypasses these capillaries.
This short circuit, known as a right-to-left shunt, has two consequences. Blood passing through the AVM does not collect oxygen, which can lower oxygen levels. More importantly, small clots, air bubbles and bacteria that would normally be trapped in the lung can pass directly into the circulation to the brain, causing stroke or brain abscess.
Pulmonary AVMs are rare. Most are linked to hereditary haemorrhagic telangiectasia (HHT), so care often involves genetics, ENT, gastroenterology, neurology and interventional radiology.
Symptoms
Many people with pulmonary AVMs have no breathing symptoms, and the first sign may be a complication. Possible features include:
- Breathlessness and reduced exercise tolerance
- Low oxygen levels, sometimes with bluish lips (cyanosis) and finger clubbing
- Stroke or transient ischaemic attack, even in young people
- Brain abscess, presenting with headache, fever or seizures
- Migraine, which is more common in people with AVMs
- Coughing up blood or bleeding into the chest, rare but serious
Features of HHT include frequent nosebleeds, small red spots on the lips, tongue or fingertips, iron-deficiency anaemia and a family history of similar problems.
Causes and risk factors
Most pulmonary AVMs are associated with hereditary haemorrhagic telangiectasia, an inherited condition caused by changes in genes such as ENG and ACVRL1. It is passed from parent to child, each child of an affected parent having a 50 percent chance of inheriting it. Family screening is therefore important.
Less commonly, AVMs occur without HHT or develop after liver disease (hepatopulmonary syndrome), certain heart surgeries for congenital heart disease, chest trauma, or infections. Pregnancy can cause AVMs to enlarge, so women with known AVMs need specialist care during pregnancy.
How pulmonary AVMs are diagnosed
| Test | What it shows |
|---|---|
| Pulse oximetry, lying and standing | Low oxygen levels, which may fall further when upright |
| Contrast (bubble) echocardiography | A right-to-left shunt through the lungs (the preferred screening test) |
| CT pulmonary angiogram | Number, size and location of AVMs and their feeding arteries |
| Pulmonary angiography | Detailed vessel anatomy, done at the time of treatment |
| Blood count and iron studies | Anaemia from HHT-related bleeding |
| Genetic testing | Confirms HHT and allows screening of relatives |
An AVM can be seen as a nodule on chest X-ray and may be mistaken for other lung lesions. Biopsy of a suspected AVM should be avoided because of the risk of bleeding. People diagnosed with HHT are usually screened for lung and brain AVMs even without symptoms.
Treatment
Embolisation
The standard treatment is transcatheter embolisation, performed by interventional radiology. A thin catheter is passed from a vein in the groin to the lung artery feeding the AVM, which is then blocked with coils or vascular plugs. This is minimally invasive and usually performed under local anaesthetic. Treatment is generally recommended for AVMs with feeding arteries large enough to be embolised, even without symptoms, to reduce the risk of stroke and abscess.
Surgery
Surgery is now rarely needed and is reserved for situations where embolisation is not possible.
Preventive measures
- Antibiotic cover before dental and certain other procedures, to reduce the risk of brain abscess
- Air filters on intravenous lines during hospital treatment, to prevent air bubbles reaching the brain
- Avoiding scuba diving
- Treating iron deficiency and managing nosebleeds with ENT
Outlook and follow-up
After successful embolisation, most people do well, and oxygen levels often improve. Small AVMs may grow or treated ones may reopen over time, so follow-up CT scanning is recommended at intervals, often lifelong. Relatives of people with HHT should be offered screening. Pregnancy should be planned with the specialist team, ideally after AVMs have been treated.
Because pulmonary AVMs can cause unexplained low oxygen, they are sometimes confused with pulmonary hypertension or interstitial lung disease. HHT itself can occasionally cause pulmonary hypertension, which needs separate assessment.
When to seek urgent care
Call emergency services immediately for sudden weakness of the face, arm or leg, difficulty speaking, or sudden severe headache, as these may indicate stroke. Seek urgent care for headache with fever or a seizure, coughing up blood, sudden chest pain with breathlessness, or heavy nosebleeds that will not stop. Pregnant women with AVMs should report any new breathlessness or haemoptysis immediately.
Frequently asked questions
If I feel well, why should my AVM be treated?
The main dangers of pulmonary AVMs are stroke and brain abscess, which can occur without warning in people with no breathing symptoms. Embolisation reduces this risk.
Is embolisation a major operation?
No. It is a minimally invasive procedure done through a vein in the groin, usually under local anaesthetic, with most patients going home within a day or two.
Should my family be tested?
If you have hereditary haemorrhagic telangiectasia, first-degree relatives should be offered screening, as HHT is inherited and AVMs can be present without symptoms.
Why do I need antibiotics before dental treatment?
Bacteria entering the blood during dental work can pass through an AVM to the brain and cause an abscess. Antibiotic cover reduces this risk, and is often continued even after embolisation.
Can I become pregnant if I have pulmonary AVMs?
Many women with AVMs have successful pregnancies, but AVMs can enlarge during pregnancy. Screening and treatment before conception, and specialist care throughout pregnancy, are advised.
Will I need scans after treatment?
Yes. Follow-up CT scans check that treated AVMs remain closed and that smaller ones have not grown.
Related conditions and procedures
Consult Dr. Gogineni Ratnakara Rao
Apollo Hospitals, Financial District: Monday to Saturday, 8:30 AM to 5:00 PM. Anything in Lung Clinic, Chanda Nagar: Monday to Saturday (Thursday closed), 6:00 PM to 9:00 PM.