Pulmonary Artery Aneurysm

Pulmonary artery aneurysm is a localised dilatation of the main, lobar or segmental pulmonary arteries. It is rare, found in about 1 in 14,000 autopsies, and defined by a main pulmonary artery diameter over 4 cm (normal under 3 cm), or a focal saccular dilatation of a branch vessel.

Causes are congenital heart disease (patent ductus arteriosus, atrial septal defect, pulmonary valve stenosis with post-stenotic dilatation), pulmonary hypertension, connective tissue disease (Marfan syndrome, Ehlers-Danlos syndrome), vasculitis (Behçet disease, Hughes-Stovin syndrome, Takayasu arteritis), infection (tuberculosis, syphilis, fungal and septic emboli), trauma, catheter injury and idiopathic disease. Behçet disease is the commonest cause of peripheral aneurysm in young men from endemic regions.

Pathophysiology. A weak or inflamed arterial wall (loss of elastic lamina and smooth muscle) dilates under pulmonary pressure. In vasculitis, perivascular inflammation destroys the media, while in pulmonary hypertension, high pressure and flow stretch the wall. The aneurysm may thrombose, dissect or rupture into the airway or pleura.

Many have no symptoms, and the aneurysm is a finding on a chest radiograph (hilar enlargement or mass). Others have dyspnoea, chest pain, cough and haemoptysis, which may be massive. Features of the cause may be present (oral and genital ulcers, uveitis, venous thrombosis, cyanosis, murmur). Compression of the bronchus, coronary artery or recurrent laryngeal nerve occurs with large central aneurysms.

Haemoptysis of any volume with a known aneurysm needs urgent assessment, since a small bleed can precede fatal rupture.

• CT pulmonary angiography: the test of choice, showing the size, shape (saccular or fusiform), mural thrombus, calcification, wall thickening and relation to the airway. Multiplanar reconstruction maps the origin and feeding vessels.
• MR angiography as an alternative, and echocardiography for the main pulmonary artery, pulmonary pressure and cardiac defects.
• Chest radiograph: hilar or mediastinal mass, enlarged pulmonary artery, and peripheral nodular opacity.
• Conventional pulmonary angiography only when intervention is planned, and right heart catheterisation is avoided with a peripheral aneurysm, because the catheter may rupture it.
• Cause: inflammatory markers, ANCA, tuberculosis tests, syphilis serology, HLA-B51 and clinical criteria for Behçet disease, and genetic testing for connective tissue disease.
• Look for deep vein thrombosis and other aneurysms (systemic arteries).

Differential diagnosis.

• Pulmonary artery sarcoma
• Hilar lymphadenopathy or lung cancer
• Pulmonary artery pseudoaneurysm
• Arteriovenous malformation
• Bronchogenic cyst
• Aortic aneurysm or pulmonary hypertension with simple dilatation

• Treat the cause: antituberculosis therapy (rifampicin 10 mg/kg, maximum 600 mg, isoniazid 5 mg/kg, maximum 300 mg, pyrazinamide 25 mg/kg and ethambutol 15 mg/kg daily for 2 months, then rifampicin and isoniazid for 4 months), antibiotics for septic aneurysm, and repair of the congenital defect.
• Behçet disease and related vasculitis: methylprednisolone 1 g intravenously daily for 3 days, then prednisolone 1 mg/kg daily with taper, together with cyclophosphamide 600 mg/m2 intravenously monthly (or 15 mg/kg) for 6 to 12 months, then azathioprine 2 mg/kg daily. Infliximab 5 mg/kg at weeks 0, 2 and 6, then every 8 weeks, is used for refractory disease.
• Avoid anticoagulation in the presence of an aneurysm (risk of fatal haemoptysis), unless thrombosis is clear and only after immunosuppression has begun.
• Endovascular treatment for symptomatic, enlarging or peripheral aneurysm: coil or plug embolisation of the feeding artery (success 80 to 90%), or covered stent placement for a central lesion with a suitable neck.
• Surgery for large central aneurysm (over 5.5 cm), rapid growth, compression, dissection or failure of endovascular therapy: aneurysmorrhaphy, graft replacement or lobectomy.
• Control of pulmonary hypertension when present (sildenafil 20 mg three times daily, or bosentan 62.5 mg twice daily increasing to 125 mg twice daily), and blood pressure.
• Haemoptysis: tranexamic acid 500 mg to 1 g orally or intravenously three times daily, bleeding side down positioning, and urgent embolisation.
• Advice to avoid strenuous straining and pregnancy counselling in connective tissue disease.

Complications and prognosis. Rupture (fatal haemoptysis or haemothorax), dissection, thrombosis with infarction, and compression. Mortality in untreated symptomatic peripheral aneurysm in Behçet disease is high (over 50% at 2 years), and improves with early immunosuppression.

Monitoring. CT angiography or MRI at 3 to 6 months after treatment and every 6 to 12 months for surveillance, with inflammatory markers and echocardiography.

Referral and escalation. Refer to a vascular and interventional radiology centre, cardiothoracic surgery, and rheumatology. Refer urgently for haemoptysis.