Evaluation of the bronchial arteries: normal findings, hypertrophy and embolization in patients with hemoptysis

The most common congenital diseases associated with bronchial artery dilatation are Tetralogy of Fallot, pulmonary agenesis, and an anomalous left coronary artery arising from the pulmonary artery (ALCAPA syndrome).

Tetralogy of Fallot is the most common cyanotic congenital heart condition. Classically, it is characterized by the combination of right ventricular outflow tract obstruction, ventricular septal defect, overriding aorta, and right ventricular hypertrophy [17]. When severe, it is associated with pulmonary valve atresia, leading to an impairment of the pulmonary arterial flow. As a response, in cases of closed ductus arteriosus, pulmonary arterial circulation is partially assured by systemic fetal vessels called major aortopulmonary collateral arteries (MAPCAs) that persist after birth to compensate the impairment of the pulmonary circulation. MAPCAs usually originate from the descending thoracic aorta and probably represent dilated bronchial arteries due to its similar origin and course (Fig. 4a–c) [18]. MAPCAs are essential to assure the pulmonary circulation in such patients until undergoing a corrective surgical procedure, when they are frequently embolized. Hemoptysis may occur, potentially originating from the aneurismal dilation of hypertrophied bronchial vessels, erosion of varicose bronchial vessels into the airway, or rupture of MAPCAs [19, 20]. Hemoptysis may be triggered by infection or co-existing clotting disorders. When it compromises the hemodynamics stability of the patient, embolization of the culprit artery is indicated [17, 20].

Agenesis of the pulmonary artery, also called proximal interruption of the pulmonary artery, is an uncommon developmental anomaly resulting in proximal absence of the pulmonary artery, with preservation of the intrapulmonary vasculature. This variant can occur on either side, more commonly on the right side, with ipsilateral lung hypoplasia [21]. When it occurs, the distal pulmonary arterial branches are usually supplied by hypertrophied bronchial arteries, internal mammary, intercostal, subdiaphragmatic, or coronary arterial collaterals (Fig. 4d).

Clinical presentation varies from asymptomatic incidental finding to massive hemoptysis due to ruptured hypertrophied systemic collaterals, rarely requiring transcatheter embolization [21].

ALCAPA syndrome is a rare congenital disease associated with an anomalous origin of the left coronary artery from the pulmonary artery trunk, leading to a right-to-left shunting. It has a high mortality rate due to myocardial infarction, explained by the diverted flow from the coronary bed to the pulmonary trunk. This is counterbalanced by the development of right coronary to left coronary artery collaterals early in life. It may be asymptomatic, being diagnosed later in childhood. In these patients, bronchial artery dilatation occurs to increase the arterial supply to the left coronary territory (Fig. 5) [22, 23].

There are several acquired diseases that can cause bronchial artery hypertrophy.

Inflammatory diseases and infection, such as bronchiectasis (Fig. 6), cystic fibrosis (Fig. 7), tuberculosis (TB), or aspergilloma (Fig. 8), may be associated with BAH. The proposed mechanism is complex, probably due to vasculitis with increased neovascularity and microvascular thrombosis of the pulmonary vessels [24, 25]. This process appears to be mediated by angiogenic growth factors, which promote the proliferation and expansion of the bronchial arteries [24].

Bronchiectasis is an acquired disorder characterized by permanent abnormal dilatation and destruction of the bronchial walls. Its pathophysiology involves an infectious insult to the airways, with impaired drainage, airway obstruction, and/or a defect in host defense. There is a multitude of etiologies associated with bronchiectasis, such as cystic fibrosis, cigarette smoking, pulmonary infections, defective host defenses, and foreign-body airway obstruction. Recurrent airway inflammation promotes neovascularity and bronchial artery dilatation, increasing the risk of hemoptysis (Figs. 6 and 7) [25].

Infection is also associated with BAH, and one of the most common agent is Mycobacterium tuberculosis. Nowadays, despite recent medical advances, TB remains a relevant health burden, particularly in developing countries. Historically, hemoptysis was considered almost pathognomonic for pulmonary tuberculosis. Hemoptysis is a potential complication of active or prior TB. Bleeding in active TB can occur in the setting of cavitary or noncavitary disease and usually results from bronchial arterial ulceration, with necrosis of adjacent blood vessels. Rarely, active TB can cause hemoptysis due to rupture of a Rasmussen’s aneurysm, which is a pseudo-aneurysm of the pulmonary artery adjacent to a tuberculous cavity. When it occurs, it may lead to life threatening massive hemoptysis, with associated high mortality rate (Fig. 8) [26].

Although strongly associated with active pulmonary TB, hemoptysis can also present following resolution of an acute disease (post-primary TB) due to airway or lung parenchymal distortion with associated vascular changes. This irreversible process leads to distortion and damage of local bronchial vascularization, which becomes hypertrophied, dilated, and exposed, with increased risk of bleeding. Other causes of hemoptysis in the setting of inactive/prior TB include the erosion of a healed calcified lymph node through a bronchial artery, bronchiectasis due to structural lung damage, and fungal colonization of prior lung cavities with Aspergillus or other species, leading to hemoptysis due to erosion of adjacent vasculature (Fig. 9) [26, 27].

Other lung infections, particularly lung abscess, can also cause hemoptysis. Bleeding may occur acutely from direct necrosis of lung tissue or in the setting of chronic inflammation, due to rupture of hypertrophied bronchial arteries [27].

BAH is a potential finding in patients with thromboembolic disease. When it occurs, the presence of dilated bronchial arteries favors chronic disease, and usually coexists on CECT with other vascular signs of chronic thromboembolic disease, such as endoluminal peripheral filling defect with obtuse margins, calcified thrombus, or a web/linear morphology (Fig. 10) [28‐30].

Secondary findings include signs of pulmonary hypertension, with increased caliber of the pulmonary arterial trunk, enlargement of the right heart cavities, and parenchymal changes with subpleural linear or wedge-shaped opacities and mosaic attenuation.

Due to chronic pulmonary ischemia, increased incidence of BAH has been reported in chronic thromboembolic disease, potentially associated with moderate-to-massive hemoptysis in 0.1% of the cases [31].

The management of hemoptysis in these patients is challenging due to the ongoing anticoagulant therapy, so even in cases of mild hemoptysis, intervention with embolization should be considered [32].

Pulmonary hypertension is a progressive disease characterized by an elevated pulmonary artery pressure (≥ 25 mmHg at rest). According to its etiology, it is classified as primary, also called pulmonary arterial hypertension (PAH), or secondary, when associated with other diseases like pulmonary thromboembolism, left heart disease, or chronic lung disease.

PAH is primarily a disease of the pulmonary circulation. It is rare, with an estimated incidence of 5–15 cases per one million, being more common in young adults [33]. It affects the small pulmonary muscular arterioles, leading to vasoconstriction, hyperplasia, fibrosis, and thrombosis. It is a severe and progressive disease, with a median survival of 2.8 years if untreated. Common imaging findings of PAH include enlargement of the pulmonary arterial trunk (> 29 mm), narrowing of the distal pulmonary arteries and associated signs of right heart strain. Although rare, BAH is a possible finding in PAH, with a reported incidence of 14%, increasing the risk of hemoptysis [34]. The mechanism of BAH in PAH is not fully understood, being probably related to tissue hypoxia with compensatory hypertrophy of the bronchial arteries. The association of BAH and hemoptysis might be related to the frailty of the hypertrophied bronchial arteries, with more tendency to rupture [35].

The number of dilated bronchial arteries appears to be linked to the increasing severity of the pulmonary arterial hypertension, as a response of the bronchial vasculature to the increasing resistance of flow in the damaged pulmonary vasculature.

Interestingly, patients with non-thromboembolic pulmonary hypertension have a much lower incidence of BAH (10–26%), compared with chronic thromboembolic disease (> 90%). This fact may be helpful in differentiating both diseases [34].

Takayasu arteritis is classified as a large-vessel vasculitis, affecting the aorta, its primary branches, and the pulmonary arteries. It mostly affects young females, usually between 10 and 40 years of age. The pathophysiology is poorly understood, probably related to cell-mediated mechanisms with infiltration of inflammatory cells in the large-vessel walls, leading to vessel narrowing, occlusion, or dilatation of the involved arteries. Imaging findings in the acute phase include large-vessel wall thickening with contrast enhancement, progressing to stenosis, or occlusion in the late phase. Bronchial artery enlargement in Takayasu arteritis is a late finding, with increased risk of hemoptysis, occurring only in patients with marked pulmonary artery stenosis or occlusion, due to chronic hypoxemia of the lung tissue [36, 37].

Fibrosing mediastinitis is an infiltrative benign process with excessive fibrotic reaction in the mediastinum, causing central obstruction of the pulmonary vessels. It is frequently sequelae of a prior local nodal infection, usually histoplasmosis, with associated residual mediastinal calcifications [38]. It can result in compromise of the airway, the esophagus, and the great vessels, with reduction of the pulmonary blood flow when it encases the pulmonary vessels. The process is generally unilateral, with ipsilateral bronchial artery dilatation to the affected site as a compensatory response to lung hypoxemia [39, 40].

Malignancy, in particular lung cancer, is a common cause of hemoptysis in older patients, being responsible for almost 25% of all cases of hemoptysis in the USA [41].

The highest incidence of bleeding occurs with squamous cell carcinoma, followed by adenocarcinoma, small cell, and large cell carcinoma [42]. The possible sources of bleeding include bronchial arterial bleed within the tumor, tumor erosion into the pulmonary artery, or systemic arterial rupture.

The widespread use of bronchial artery embolization in the management of hemoptysis contributed to a decrease of the mortality rate, with a success rate of 77–82% in immediate bleeding control [43, 44].