Introduction
Unilateral absence of pulmonary artery is an extremely rare congenital anomaly, occurring in approximately 1 in 200,000 to 300,000 adults. Most cases are associated with other major cardiac anomalies such as Tetralogy of Fallot, Reference Abraham, Cherian, Rao, Sukumar, Krishnaswami and John1 patent ductus arteriosus (PDA), Reference Koga, Hidaka, Miyako, Suga and Takahashi2 coarctation of the aorta, Reference Wyman3 atrial septal defect, Reference Wang, Yuan, Shi and Xu4 or truncus arteriosus. Isolated cases constitute about 40%. Reference Pool, Vogel and Blount5 Unilateral absence of pulmonary artery is twice as common on the right side compared to the left Reference Wang, Yuan, Shi and Xu4 and results from developmental failure of the sixth aortic arch to fuse with the pulmonary trunk.
Because of its rarity, the diagnosis of unilateral absence of pulmonary artery in neonates and infants is usually incidental. Approximately 400 cases have been reported worldwide. Neonates and infants are often asymptomatic, Reference Patil6 with the median age of diagnosis reported as 14 years. Reference Mohan, Mohan and Tandon7
Due to its subtle presentation, diagnosis is challenging. Non-invasive cardiac imaging such as transthoracic echocardiography and cardiac CT/MRI is central to diagnosis. However, no clear guidelines exist for treatment because of the rarity of this anomaly.
We report a neonatal case of absent right pulmonary artery, incidentally diagnosed during evaluation for cardio-respiratory distress.
Case report
A 21-day-old male infant (2.35 kg) presented with persistent tachypnea and desaturation from day 10 of life. Initial evaluation at a local hospital was inconclusive, and the infant was referred to our centre.
On admission, he was haemodynamically stable with no cyanosis. ECG and chest X-ray were unremarkable. Transthoracic echocardiography revealed normal cardiac anatomy and biventricular function, with an intact septum and normal pulmonary venous return. The great vessels were normally related. A dilated main pulmonary artery (17 mm) was visualised, continuing as a normal left pulmonary artery; however, the right pulmonary artery was not visualised despite multiple attempts (Figure 1). Moderate-to-severe tricuspid regurgitation and moderate pulmonary hypertension were noted (Figure 2).
Continuation of dilated MPA as the left pulmonary artery and non-visualisation of RPA.
Presence of moderate to severe tricuspid regurgitation.
Anomalous origin of the right pulmonary artery was considered, but suprasternal imaging showed no anomalous right pulmonary artery origin (Figure 3). A provisional diagnosis of unilateral absence of pulmonary artery was made. Cardiac contrast-enhanced CT and aortography confirmed the absence of right pulmonary artery, the absence of aorto-pulmonary collaterals, and a relatively avascular right lung (Figure 4).
Supra-sternal notch view showing absence of anomalous RPA origin or aorto-pulmonary collaterals.
Cardiac CECT with pulmonary angiography showing absent RPA (blue arrow), hypo-vascular right lung (white arrow), aortic arch doesn’t show anomalous origin of RPA or any collaterals (red arrow), and dilated MPA (green arrow).
The infant was referred for surgical consultation and multidisciplinary evaluation. In view of the risk of cardiac failure and recurrent respiratory infections, close medical follow-up was initiated after thorough parental counselling.
Discussion
Isolated unilateral absence of pulmonary artery is a rare congenital anomaly, typically diagnosed in adolescence or adulthood. Many cases remain undetected in childhood, presenting later with recurrent respiratory tract infections, haemoptysis, chest pain, cardiac failure, or pulmonary hypertension. The disease course depends partly on the presence of systemic collaterals supplying the ipsilateral lung. Unilateral absence of pulmonary artery affects the right lung in about two-thirds of cases. Reference Ten Harkel, Blom and Ottenkamp8
Our patient presented with neonatal respiratory distress, a rare presentation. Possible mechanisms of morbidity include recurrent infections due to impaired immune cell trafficking and mucus trapping (leading to bronchiectasis), haemoptysis from systemic collaterals, and pulmonary hypertension resulting from shear stress on the contralateral pulmonary artery and vasoconstriction of arterioles.
First-line investigation is echocardiography, which can screen for congenital anomalies and demonstrate absent visualisation of one pulmonary artery. Cardiac CT/MRI is essential for confirmation. Although cardiac catheterisation and angiography are the gold standard, they are invasive and not always required for diagnosis.
Management guidelines are lacking because of disease rarity. Medical management typically involves anti-failure therapy and pulmonary vasodilators. Surgical options, when feasible, include pulmonary artery reconstruction with conduit placement, Reference Yan, Cen and Luo9 staged reconstruction following Blalock-Taussig shunt. Reference Hiramatsu, Komori, Okamura, Suzuki, Takeuchi and Shibuta10 or creation of an aorto-pulmonary shunt.
Conclusion
Unilateral absence of pulmonary artery is a rare but important cause of pulmonary hypertension. Early diagnosis is challenging but critical. Echocardiography and CT/MRI remain cornerstones of diagnosis. Prompt recognition ensures close follow-up, timely initiation of therapy, and potential surgical intervention.
Learning points
• In primary care, neonates with unexplained tachypnea, desaturation, or recurrent lower respiratory tract infections should be referred for echocardiography to rule out rare vascular anomalies like unilateral absence of pulmonary artery.
• Chest X-ray may show asymmetric vascular markings, with absent hilar vascular shadow on the affected side providing an early clue.
• Pulse oximetry showing persistent desaturation despite normal systemic examination should prompt referral.
• Echocardiography is the first-line tool for suspected cases; absence of one pulmonary artery should raise suspicion. Confirmation requires cardiac CT/MRI.
• Early suspicion and referral from primary care are crucial to ensure timely multidisciplinary management and consideration of surgical options.
