Aetiology

Acute and chronic bronchitis, and less commonly tuberculosis and bronchiectasis, have been reported as major causes of haemoptysis.[8][9] Malignancy is a common cause of massive or life-threatening haemoptysis.[3]

Pulmonary vascular anatomy

The tracheobronchial tree and the lungs have a dual circulation:

  • Bronchial arteries (systemic circulation)

  • Pulmonary arteries.

The bronchial arteries are branches of the aorta or its tributaries, the intercostal arteries, and carry systemic arterial pressures that perfuse the adjacent airways to the level of the terminal bronchioles. Bronchial arteries supply the mediastinum, hilar lymph nodes, and visceral pleura.

The pulmonary artery is a low-pressure system, with normal systolic pressures ranging from 15 to 20 mmHg and diastolic pressures of 5 to 10 mmHg. These vessels supply the pulmonary parenchyma and the respiratory bronchioles. The anastomotic connections between the bronchial circulation and the pulmonary circulation contribute to physiological right-to-left shunt.[1]

Clinical, radiological, and pathological evidence has demonstrated that the systemic circulation (bronchial arteries) is responsible for most cases of haemoptysis.[10]

Haemoptysis from the pulmonary circulation may occur in catheter-induced pulmonary artery rupture, vasculitis, pulmonary artery aneurysms due to collagen vascular disease, necrotic pulmonary infection, or pulmonary arteriovenous malformation such as in hereditary haemorrhagic telangiectasia.[11][12][13]

Infectious

Infection is one of the most common causes of haemoptysis.

  • Pneumonia: can cause haemoptysis by causing necrosis of adjacent bronchial vessels or local mucosal ulceration.

  • Chronic fibrotic tuberculosis: haemoptysis is caused by rupture of Rasmussen's aneurysms or ectatic pulmonary arteries (with a weakened adventitia and media vessels) traversing the tuberculous cavities.

  • Bronchiectasis: chronic airway inflammation results in increased bronchial artery tortuosity, as well as proliferation of the capillary beds and peribronchial vascular plexus. Recurrent inflammatory destruction and healing lead to bronchopulmonary vascular anastomoses.[14][15][16]

  • Lung abscess: the pathogenesis of haemoptysis is not entirely clear but may be due to progression of local inflammatory processes causing necrosis of branches of the pulmonary artery.[17]

  • Mucormycosis: may cause massive haemoptysis.[18]

Neoplastic

In malignancy, there is an increase in the bronchial artery supply to the region of the tumour. Haemoptysis results from necrosis, mucosal invasion, or direct local invasion of a blood vessel. Massive haemoptysis may happen when tumour invasion into a blood vessel and its adjacent airway results in vascular airway fistula.

Iatrogenic

Haemoptysis may occur with traumatic intubation, bronchoscopy, lung biopsy and endobronchial therapeutic manoeuvres. Massive fatal haemoptysis may rarely happen from erosion of a tracheostomy or laryngectomy into an innominate (brachiocephalic) artery.

Other causes include catheter-induced pulmonary artery rupture or infarct. Drug-induced haemoptysis may occur with exposure to anticoagulants, aspirin, and thrombolytic agents.

Vasculitic

Haemoptysis may be found in patients with pulmonary haemorrhage from a small-vessel vasculitis (such as granulomatosis with polyangiitis [formerly Wegener's granulomatosis]), and may be the presenting symptom in some patients.

The mechanisms responsible for haemoptysis in vasculitis are multiple. However, the most important is pulmonary haemorrhagic alveolar capillaritis. This involves neutrophilic infiltration of the alveolar septa, where disruption of the alveolar-capillary basement membranes results in extensive haemorrhage into the alveolar spaces.[19][20] Cigarette smoking has been associated with increased risk of vasculitis.[21]

Though infrequently clinically feasible in the acutely bleeding patient, an elevated value of diffusing capacity can indicate alveolar bleeding because intra-alveolar blood adsorbs carbon monoxide avidly.

Cardiac

In left ventricular failure and mitral stenosis, blood-streaked sputum is caused by rupture of pulmonary veins or capillaries, or by anastomoses between the bronchial and pulmonary arteries distended by elevated intravascular pressure or pulmonary venous hypertension.[14][22][23]

Vascular

Vascular anomalies such as Dieulafoy's disease, characterised by the presence of a tortuous dysplastic artery in the submucosa, can be a cause of haemoptysis.[24] Pulmonary arteriovenous malformation may also cause haemoptysis. Pulmonary thromboembolic disease that progresses to pulmonary infarct may result in haemoptysis and bloody pleural effusion.

Haematological

Haemoptysis can be caused by bleeding and coagulation-related disorders or abnormalities, such as thrombocytopenia, coagulopathies, or disseminated intravascular coagulation.

Congenital

Congenital lung malformations such as bronchogenic cyst can cause haemoptysis.

Idiopathic

Idiopathic haemoptysis is a diagnosis of exclusion. In approximately one third of patients presenting with haemoptysis, the underlying cause is not identified even after careful assessment.

Miscellaneous

Thoracic endometriosis has been associated with haemoptysis.[25]

Factitious

Factitious haemoptysis is a diagnosis of exclusion.[26] However, factitious haemoptysis is likely to be both under-reported and under-diagnosed. Because factitious haemoptysis is an exclusionary diagnosis, patients with factitious disorders frequently undergo multiple invasive and non-invasive studies before the diagnosis is made.[26]​[27]​​

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