Understanding Unilateral Pulmonary Artery Absence and Hemoptysis

Congenital unilateral pulmonary artery absence represents a rare vascular anomaly caused by incomplete development of the sixth aortic arch. Patients frequently remain asymptomatic during childhood because compensatory collaterals maintain adequate pulmonary blood flow. However, young adults often develop alarming symptoms, including recurrent respiratory infections, exercise intolerance, or sudden hemoptysis. A notable case involved a young male who experienced hemoptysis years after surgical closure for patent ductus arteriosus. Furthermore, clinicians initially suspected routine parenchymal disease, delaying recognition of the true vascular defect. Subsequent computed tomography angiography demonstrated complete absence of the right pulmonary artery. Instead, an anomalous vessel originating directly from the aortic arch supplied the right lung. This scenario highlights how high-pressure systemic collaterals undergo progressive structural remodeling over decades. Consequently, thin-walled neovascular channels become fragile and vulnerable to spontaneous rupture under systemic pressures. Clinicians must actively expand their differential diagnosis when patients with repaired congenital lesions present with hemoptysis. Therefore, prompt recognition prevents catastrophic hemorrhage.

Embryologic Malformation and Systemic Collateral Formation

The embryologic origins of this disorder involve premature involution of the proximal sixth aortic arch during gestational organogenesis. Meanwhile, the distal portion fails to connect with the central pulmonary trunk. Consequently, the ipsilateral lung parenchymal architecture relies entirely on compensatory systemic arterial circulation for tissue viability. Over time, bronchial arteries, intercostal vessels, and internal thoracic arteries enlarge to deliver systemic oxygenated blood. In this patient, an abnormal vessel arose directly from the aortic arch to supply the isolated lung. Because this vessel originates from the aorta, it carries blood under high systemic pressure rather than low pulmonary arterial pressure. Chronic exposure to systemic pressure produces progressive vascular remodeling, smooth muscle hypertrophy, and microaneurysm formation. Furthermore, local tissue ischemia releases angiogenic factors that stimulate thin-walled, disorganized capillary networks. When systemic blood pressure spikes or airway inflammation occurs, these fragile collateral networks rupture into adjacent bronchial lumens. Thus, patients experience recurrent, unpredictable bouts of hemoptysis requiring urgent diagnostic localization.

Hemodynamic Consequences Following Surgical PDA Closure

The patient's prior surgical repair of a patent ductus arteriosus provides critical insights into collateral vessel progression. Before surgical correction, the patent ductus arteriosus maintained a persistent left-to-right shunt. However, surgical ligation abruptly eliminated this shunting pathway and redirected total right ventricular stroke volume into the single contralateral pulmonary artery. Consequently, the solitary left pulmonary artery accommodated the entire pulmonary circulation, increasing pulmonary vascular resistance and shear stress. Simultaneously, systemic arterial hemodynamics reorganized after surgeons closed the ductal runoff. Because systemic perfusion pressures stabilized at higher levels, the anomalous collateral vessel originating from the aortic arch experienced amplified hemodynamic force. Furthermore, this sustained pressure gradient accelerated structural degeneration within the collateral vascular wall over subsequent years. In addition, the prolonged interval between pediatric ductal closure and adult hemoptysis allowed these microvascular alterations to develop silently. Clinicians must therefore recognize that closing an extracardiac shunt can inadvertently accelerate pathological remodeling in coexisting, undetected vascular anomalies.

Diagnostic Value of Computed Tomography Angiography

Accurate identification of this vascular malformation requires advanced cross-sectional imaging rather than radiography alone. Routine chest radiographs often reveal non-specific findings, such as ipsilateral hemithorax volume reduction and mediastinal shift. However, clinicians frequently misinterpret these radiographic clues as chronic atelectasis or post-infectious fibrosis. Contrast-enhanced computed tomography pulmonary angiography serves as the definitive gold standard diagnostic tool. In this case, computed tomography angiography clearly confirmed the complete absence of the right pulmonary artery. Moreover, the study traced the anomalous systemic vessel arising directly from the aortic arch into the right lung. Beyond vascular anatomy, high-resolution computed tomography assesses parenchymal complications, including mosaic perfusion and bronchiectasis. Furthermore, three-dimensional reconstructions accurately map the course of all non-bronchial systemic collaterals. Transthoracic echocardiography must also accompany radiological imaging to evaluate right ventricular systolic function and rule out pulmonary hypertension. Therefore, multidetector computed tomography provides indispensable guidance for subsequent interventional planning.

Clinical Management and Interventional Embolization Strategies

Management depends on the severity of hemoptysis, collateralization extent, and baseline pulmonary arterial pressures. Conservative therapy with bed rest, cough suppressants, and antibiotics may manage minor bleeding episodes. However, active or massive hemoptysis represents an acute emergency that requires rapid endovascular intervention. Transcatheter arterial embolization serves as the primary treatment of choice for controlling acute hemorrhage. Interventional radiologists selectively cannulate the anomalous aortic arch vessel and hypertrophied collaterals using microcatheters. Subsequently, they deploy embolic agents, such as polyvinyl alcohol particles or microcoils, to occlude bleeding vessels. Although transcatheter embolization achieves immediate hemostasis, neovascular recruitment can cause recurrent hemoptysis over time. Consequently, physicians must maintain regular surveillance using clinical assessments and repeat vascular imaging. If recurrent hemorrhage resists repeat embolization, or if severe localized lung destruction occurs, surgical pneumonectomy provides a definitive cure. Furthermore, patients with concurrent pulmonary hypertension require targeted vasodilators to protect the single functioning lung.

Long-Term Clinical Surveillance and Multidisciplinary Care

This case underscores the essential need for lifelong surveillance in adults who underwent pediatric congenital cardiac surgery. First, pediatric closure of a patent ductus arteriosus does not eliminate coexisting vascular anomalies. Second, clinicians must investigate unexplained hemoptysis aggressively with computed tomography angiography rather than assuming benign etiology. Because systemic collaterals rupture under arterial pressures, prompt endovascular localization prevents catastrophic hemorrhage. Furthermore, adult congenital cardiologists, pulmonologists, and interventional radiologists must collaborate closely to optimize outcomes. Periodic echocardiography remains vital to monitor pulmonary pressures in the solitary perfused lung. If pulmonary hypertension develops, early medical management preserves right ventricular function. In addition, educating patients regarding warning signs ensures timely medical evaluation during recurrent episodes. Ultimately, broadening diagnostic reasoning when evaluating patients with prior cardiac repairs ensures accurate diagnosis and improves long-term survival.

How does unilateral pulmonary artery absence cause recurrent hemoptysis?

The absence of a main pulmonary artery forces the affected lung to recruit systemic collateral vessels, including hypertrophied bronchial and anomalous aortic branches. Because these collateral vessels originate directly from the high-pressure systemic circulation, their thin-walled microvascular networks experience severe wall shear stress. Over time, chronic pressure leads to vascular dilation, tortuosity, and aneurysm formation. Eventually, minor physical exertion or local inflammation causes these fragile systemic vessels to rupture into the bronchial airways, precipitating hemoptysis.

Why can patent ductus arteriosus closure exacerbate systemic collateral bleeding?

Patent ductus arteriosus closure terminates the left-to-right extracardiac shunt, which abruptly redirects the total cardiac output through the solitary contralateral pulmonary artery. Consequently, pulmonary vascular resistance and systemic hemodynamic pressures undergo profound redistribution. The sudden normalization of systemic arterial pressure increases mechanical perfusion stress across fragile anomalous vessels supplying the ipsilateral lung. Furthermore, eliminating ductal runoff intensifies collateral blood flow. Over time, these hemodynamic shifts accelerate vessel wall degeneration and heighten the risk of vascular rupture.

What is the definitive diagnostic method for this vascular anomaly?

Computed tomography pulmonary angiography represents the gold standard diagnostic technique for confirming pulmonary artery absence. Multidetector contrast-enhanced imaging demonstrates the abrupt cutoff of the main pulmonary artery branch and details the parenchymal morphology. Furthermore, it precisely maps anomalous collateral vessels originating from the aortic arch, intercostal, or internal mammary arteries. This comprehensive anatomical evaluation differentiates congenital agenesis from acquired pulmonary thromboembolism and provides crucial guidance for endovascular embolization or surgical planning.

Disclaimer: This content is for informational and educational purposes only... Refer to the latest local and national guidelines for clinical practice.

References

Dong XL et al. [Congenital unilateral absence of pulmonary artery: a case report]. Zhonghua Jie He He Hu Xi Za Zhi. 2026 Sep 12. doi: 10.3760/cma.j.cn112147-20260308-00131. PMID: 42706209.

Wang P, Yuan L, Shi J, et al. Isolated unilateral absence of pulmonary artery in adulthood: a clinical analysis of 65 cases from a case series and systematic review. J Thorac Dis. 2017;9(12):4988-4996.

Kruzliak P, Syamasundar RP, Novak M, et al. Unilateral absence of pulmonary artery: pathophysiology, symptoms, diagnosis and current treatment. Arch Cardiovasc Dis. 2013;106(8-9):448-454.