Pulmonary Artery Pseudoaneurysm

Pulmonary artery pseudoaneurysm is a contained rupture of a pulmonary artery in which the wall is formed by thrombus and surrounding tissue only, lacking the three arterial layers. It is a rare but dangerous cause of massive haemoptysis.

The classical cause is a Rasmussen aneurysm, in which a tuberculous cavity erodes the adjacent artery (in about 4 to 5% of cavitary tuberculosis at autopsy). Other causes are pulmonary artery catheter injury (balloon inflation or catheter in a distal branch, in 0.1 to 0.2% of catheterisations), lung abscess and necrotising pneumonia, fungal infection (aspergilloma), septic emboli, chest trauma, lung cancer, surgery and biopsy, radiofrequency ablation and Behçet disease.

Pathophysiology. Erosion, inflammation or mechanical injury disrupts the wall, and blood escapes into a cavity bounded by fibrous tissue. Pressure in the pulmonary arterial system is low but the sac expands, and rupture into a bronchus or the pleura causes bleeding. The bronchial arteries are not involved, so bronchial artery embolisation alone often fails to stop it.

Haemoptysis, ranging from streaks to massive (over 200 to 600 mL in 24 hours), often sudden. Warning haemoptysis days before is common, as is chest pain and dyspnoea. A background of cavitary tuberculosis, bronchiectasis, lung abscess or a recent catheter is usual. Rupture into the pleura gives haemothorax.

Any haemoptysis in a patient with a cavity or recent pulmonary artery catheter needs urgent assessment, since the next bleed may be fatal.

• CT angiography with multiphase contrast: a round enhancing sac adjacent to a cavity or lesion, filling in the arterial phase and washing out in the portal phase, with a contrast blush, thin or irregular wall and an adjacent haematoma. Scan during active bleeding when stable.
• Chest radiograph: a new nodule or mass in a cavity wall (a cavity with a mural nodule), consolidation from aspirated blood, or a new opacity after catheter placement.
• Bronchoscopy to localise the bleeding side and clear the airway, and rigid bronchoscopy for massive bleeding.
• Pulmonary angiography: confirms the lesion and allows treatment. Selective bronchial angiography to look for coexisting systemic supply.
• Cause: sputum smear, culture and nucleic acid test for tuberculosis, fungal markers (galactomannan), cultures, and review of catheter history.
• Full blood count, coagulation, and group and crossmatch.

Differential diagnosis.

• Bronchial artery haemorrhage (the commonest source of haemoptysis)
• Aspergilloma
• Lung cancer
• Pulmonary arteriovenous malformation
• Pulmonary artery aneurysm

• Resuscitation with airway protection: position the bleeding side down, give oxygen, secure intravenous access, and intubate early with a large bore tube. Selective intubation of the non-bleeding lung or a bronchial blocker for massive bleeding. Correct coagulopathy, and transfuse as needed.
• Tranexamic acid 1 g intravenously over 10 minutes, then 1 g every 8 hours (or 500 mg to 1 g orally three times daily), and nebulised tranexamic acid 500 mg three times daily has been used.
• Endovascular embolisation is the first line treatment: coils, vascular plugs, N-butyl cyanoacrylate glue or liquid embolic, placed in the sac and the feeding artery ("front door and back door"). Success is 90% or more, with a risk of recurrence by collateral supply and infarction. A covered stent is an alternative for larger arteries.
• Surgery (lobectomy, pneumonectomy, or aneurysm ligation) when endovascular treatment fails, in massive bleeding with instability, or for a destroyed lung. Operative mortality is higher in emergencies.
• Treat the cause: antituberculosis therapy for 6 to 9 months (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), antifungal treatment (voriconazole 400 mg twice daily on day 1 then 200 mg twice daily) for aspergillosis, and antibiotics for abscess.
• Catheter related: stop wedging and balloon inflation, remove the catheter, and embolise early. Avoid anticoagulation.
• Prevention: do not leave a pulmonary artery catheter wedged, inflate the balloon only as needed, and avoid advancing distally in anticoagulated patients or those with pulmonary hypertension.

Complications and prognosis. Mortality is 50% or more in massive bleeding without treatment, and falls to under 10 to 15% with early embolisation. Recurrent bleeding and infarction may occur.

Monitoring. CT angiography at 1 to 3 months to confirm thrombosis, then at 6 to 12 months, and sputum and clinical review during treatment of the cause.

Referral and escalation. Refer immediately to interventional radiology, thoracic surgery and intensive care.