Congenital Pulmonary Artery Anomalies: What Every Radiologist Should Know

Pulmonary artery sling

In patients with a pulmonary artery sling (PAS), also referred to as an aberrant left pulmonary artery (ALPA), the LPA arises abnormally from the posterior aspect of the right pulmonary artery (RPA) [2]. PAS is classified into two types based on the level of LPA origin and the associated airway anatomy. Type I originates just above the carina (T4–T5), with or without a tracheal bronchus. In contrast, type II arises at a lower level (T5–T6) and is frequently associated with long‑segment tracheal stenosis and abnormal bronchial branching, such as a bridging bronchus (Figures 1 and 2) [2]. Barium esophagography may also show an anterior indentation of the esophagus in PAS patients [3].

Figure 1

Figure 2

Treatment depends on clinical symptoms and anatomy. Asymptomatic patients can be monitored clinically, whereas patients with respiratory symptoms require the reimplantation of the LPA to the left [2].

Partial anomalous left pulmonary artery

Partial anomalous left pulmonary artery, also referred to as duplicated LPA, is an exceptionally rare congenital vascular variant. It is defined by the presence of an arterial branch originating from the RPA and supplying the left lung, while a normally arising LPA is also present [4–6] (Figure 3). Most anomalous branches course toward the left lower lobe [5]. Partial anomalous left pulmonary arteries are classified by their position relative to the tracheobronchial tree: anterior, anteroinferior, or posterior. The posterior type forms a partial PAS, and this entity should be distinguished from a left PAS, in which the entire LPA arises aberrantly from the RPA [7, 8].

Figure 3

Idiopathic dilatation of the pulmonary trunk

Idiopathic dilatation of the pulmonary trunk is a rare entity characterized by abnormal enlargement of the pulmonary trunk without abnormal cardiac or extracardiac shunts, cardiac disease, or pulmonary disease [9]. It is a diagnosis of exclusion, made after ruling out conditions that could dilate the pulmonary trunk, including pulmonary hypertension, connective tissue disorders, or cardiac disease (mainly pulmonary valve stenosis). Normal pressure in the RV and pulmonary artery must be confirmed using invasive angiography [10].

Chest radiography may show bulging of the left mediastinal border, while contrast‑enhanced CT or MRI can confirm the abnormal enlargement of the main pulmonary trunk, with or without dilatation of both main pulmonary arteries (Figure 4) [11]. Although definite surgical guidelines are not available, surgery is typically suggested for symptomatic patients or when the pulmonary artery diameter exceeds 5 cm [9, 12].

Figure 4

Proximal interruption of the pulmonary artery

Proximal interruption of the PA is a rare congenital anomaly characterized by the abrupt termination of the PA near the hilum. The affected lung is perfused via systemic collaterals—primarily bronchial arteries, with contributions from the intercostal, internal mammary, subclavian, and innominate arteries [13, 14]. These collateral vessels may become hypertrophied, predisposing patients to hemoptysis. Although some remain asymptomatic, most present during adolescence or early adulthood with recurrent infections, exertional dyspnea, or hemoptysis [15].

Chest radiographs of this condition typically show ipsilateral lung volume loss with a small hilum, mediastinal shift, and compensatory hyperinflation of the contralateral lung [15]. Curvilinear or reticular opacities in the subpleural lung may represent enlarged collateral vessels (Figure 5a) [13, 14].

Figure 5

CT allows for a definitive diagnosis by demonstrating the complete absence or termination of the affected PA within 1 cm of its origin. Collateral vessel hypertrophy can also be directly visualized. Additional findings may include serrated pleural thickening and parenchymal bands, reflecting transpleural collaterals bridging the systemic and peripheral pulmonary vessels [15]. Lung perfusion scintigraphy can demonstrate complete unilateral absence of perfusion, indicating systemic collateral supply to the affected lung (Figure 5b–5d) [16].

Treatment is not required if there are no signs of cardiopulmonary compromise. However, surgery is suggested for patients with life‑threatening infections or hemorrhages [17].

Pulmonary stenosis

Pulmonary stenosis (PS), which is predominantly congenital, is most commonly of valvular origin (approximately 90% of cases), followed by subvalvular (infundibular) and supravalvular types [18]. Valvular PS is typically caused by a dome‑shaped pulmonary valve (PV) and, less commonly, dysplastic, bicuspid, and quadricuspid PV [19]. The severity of obstruction determines clinical presentation, which may range from incidental findings in mild PS to systemic venous congestion in moderate to severe PS [18].

Chest radiography may demonstrate post‑stenotic dilatation of the main pulmonary artery and the LPA due to the direction of the high‑pressure blood flow across the stenotic valve, resulting in asymmetric hila or a prominent left mediastinal contour (Figure 6a). Contrast‑enhanced CT can depict this dilatation and may show secondary signs such as right ventricular hypertrophy or enlargement. Thickening and fusion of the valve leaflet, narrowing of the valve orifice, or bulging of the PV can be evaluated on ECG‑gated CT [18, 19] (Figure 6b–6d).

Figure 6

Balloon valvuloplasty is the treatment of choice in patients with hemodynamically significant valvular PS [11].