Isolated unilateral absence of pulmonary artery (IUAPA) in adults: A case series and review of literature

Unilateral Absence of Pulmonary Artery (UAPA) is a rare congenital malformation that is usually associated with cardiac anomalies. When there is no congenital cardiac abnormality it is rarer still and is termed isolated unilateral absence of pulmonary artery (IUAPA) (4). IUAPA may remain undetected until adulthood and frequently found incidentally on imaging for other indications. Symptoms are usually secondary to complications which include pulmonary hypertension, recurrent respiratory tract infections, bronchiectasis and haemoptysis. We report two cases with widely contrasting presentation and trajectories, leading to individualized management strategies.

Keywords: congenital; haemoptysis; isolated unilateral absence of pulmonary artery; symptoms; treatment

IUAPA is a rare anatomical anomaly with vast majority of patients remaining to be asymptomatic to adulthood leading to delay in diagnosis. The severity of disease as well as rate of complication varies among patients. We present two cases with contrasting trajectories and management outcomes.

Unilateral absence of pulmonary artery (UAPA) is a rare congenital anatomical abnormality which is often associated with congenital heart defects. About 30% of those with no congenital cardiac anomalies have isolated unilateral absence of pulmonary artery (IUAPA). IUAPA in adults is often detected incidentally on chest computer tomography (CT) imaging performed for other indications. There is limited knowledge on the incidence, presentation and management of IUAPA. We report two cases of IUAPA which have contrasting presentations leading to differing management strategies, and a review of the literature.

A 37‐year‐old man was reviewed in the respiratory clinic for 20‐year history of chronic productive cough. He reported daily cupful sputum production and a susceptibility to respiratory tract infection since he was a teenager. He experienced dyspnoea and dizziness on exertion. There was no history of chest pain, haemoptysis or syncope. He was born prematurely and had a stillborn twin sibling. His medical history included Crohn's colitis well‐controlled with infliximab infusions for the past 5 years and latent tuberculosis for which he had completed treatment. On examination, his right chest size was smaller than the left, with reduced respiratory excursion. Chest auscultation demonstrated reduced breath sounds and course crackles on the right side. The left side examined normally. He had dual heart sounds with no murmurs.

Plain film chest radiograph showed contracted right hemithorax, raised right hemidiaphragm, and right lower lobe bronchial wall thickening. Left lung was hypertrophied and had normal lung fields. A contrast CT chest identified unilateral absence of pulmonary artery (UAPA), hypoplastic right lung, compensatory left lung hypertrophy and right lung bronchiectasis. The pulmonary trunk appeared to be of normal diameter. Review of imaging identified a non‐contrast CT chest performed 4 years which suggested right pulmonary agenesis, but no referral was initiated. A transthoracic echocardiogram showed normal cardiac function, no congenital anomalies and no pulmonary hypertension. Lung function test was of mild restrictive pattern, with TLC of 5.6 L (76%), normal FEV1/FVC ratio, without bronchodilator response. He also had normal gas exchange.

He was provided with counselling, and chest physiotherapy for education on sputum clearance strategies. Lung protection strategies including annual flu vaccinations, early antibiotic therapy for exacerbations and avoidance of sick contacts were advised. CT surveillance was planned in 24 months.

A 30‐year‐old man presented to an emergency department at a secondary hospital with persistent low volume frank haemoptysis in the absence of infective symptoms. His background medical history includes known congenital right lung hypoplasia and well‐controlled asthma. He underwent a flexible bronchoscopy which showed a small right lower lobe endobronchial polypoid lesion which was suspected to be the culprit. He was referred to a tertiary care hospital for an elective therapeutic bronchoscopy. During repeat flexible bronchoscopy, lower lobe lesion was not identified. A right upper lobe mucosal lesion was visualized and bled briskly following contact, resulting in rapid development of hypoxia and the procedure was abandoned.

The patient was intubated, stabilized and transferred to Intensive care unit. A repeat bronchoscopy 24 h later showed persistent bleeding. CT pulmonary angiogram demonstrated hyperplastic right lung, absent right pulmonary artery, and right bronchial artery hypertrophy (Figure 1). Following a multi team conference, the patient proceeded to have a video‐assisted thoracoscopic surgery (VATS) right upper lobectomy. He recovered well from the surgery. Histopathology from the surgery showed evidence of hyperplastic and abnormal pleural intralobular and bronchial vasculature.

At the 12‐month follow up, he denied any further haemoptysis and a Ventilation perfusion (VQ) scan demonstrated 0% perfusion of the right lung (Figure 2), and 100% perfusion of the left lung. It was recommended that in the event of massive haemoptysis in the future, a right pneumonectomy would be indicated.

Unilateral absence of pulmonary artery (UAPA) is a rare congenital abnormality arising from the failure of the proximal 6th aortic arch to connect with the pulmonary trunk during embryologic development.[1] It was first described in 1868 by Frantzel O. Angeborener and was proven by Madoff et al in 1953 through angiography. The prevalence rate is estimated to be approximately one in 200,000.[2] Most patients with UAPA are found to also have congenital heart defects, such as tetralogy of Fallot, atrial septal defects, truncus arteriosus and more.[1]

A study conducted among 352 patients with UAPA in 2011 revealed that around 30% of patients with UAPA did not have cardiac anomalies. Those patients were termed to have isolated unilateral absence of pulmonary artery (IUAPA).[[3]] Patients with IUAPA tend to have mild to no symptoms often delaying diagnosis to adulthood. A systematic review of 65 adults with IUAPA by Ping Wang et al in 2017 found that 85% of patients with IUAPA were symptomatic. However, as patients largely present with non‐specific symptoms, the median duration between onset of symptoms to final diagnosis was 5 years.[1] On the contrary, those with associated cardiac anomalies tend to present in childhood.

Patients with IUAPA most commonly present with exercise intolerance or breathlessness (40%).[3] Other symptoms include haemoptysis and recurrent pulmonary infections, which are reflected in the two cases we reported.

Diagnosis of IUAPA can be challenging and many cases are diagnosed incidentally on chest imaging performed for other indications with varying relation to the disease. Chest radiograph typically demonstrates asymmetrical lung fields, with missing hilar markings on the affected side as well as a smaller hemithorax with raised hemidiaphragm on that side as demonstrated in chest radiograph for Case 1. The mediastinum can also be shifted towards the affected side, with hyperinflation of the contralateral lung. However, the gold standard for diagnosis is a computed tomography pulmonary angiogram (CTPA), which will reveal the absent pulmonary artery. Bronchiectasis and formed collateral circulation are also commonly seen. Further evaluation with a transthoracic echocardiogram to exclude cardiac anomalies and to assess for the presence of pulmonary hypertension is recommended. VQ scans commonly demonstrate absence of perfusion on the affected side in patients with IUAPA.

Clinicians should keep in mind that the radiological findings are non‐specific and could also be due to bronchiectasis, chronic pulmonary embolism, pulmonary vasculitis or Swyer‐James‐Macleod syndrome (SJMS), a rare complications of childhood respiratory tract infections leading to small airway obstruction, air trapping and unilateral radiographic hyperlucency.[1]

Patients with IUAPA when symptomatic, are often secondary to complications. Bronchiectasis and recurrent respiratory infections are not uncommon complications. In the older cohort, excessive collateral circulation predisposes to haemoptysis or pulmonary haemorrhage. Between 19% and 44% patients develop pulmonary hypertension as a result of long‐term vasoconstriction and increased vessel resistance.[3] Thus far, apart from the relationship between age and presence of haemoptysis, we were unable to find literature supporting other risk factors for severe complications among patients with IUAPA.

There are no studies or consensus recommendations on how to manage adults with IUAPA. Treatment is guided by symptoms, complications and extent of pulmonary hypertension.[3] Mild cases, as described in our first case, should be followed up regularly with surveillance imaging and/or echocardiogram. Non‐pharmacological lung protective strategies could also be effective in preventing or delaying the onset of complications. Patients with pulmonary hypertension are managed with oral phosphodiesterase inhibitors or endothelin receptor agonists to improve symptoms and function.[1] It is important to note that patients who develop pulmonary hypertension tend to have poorer prognosis.[5] In the younger cohort, early revascularisation is an option, however this is contraindicated in older patients as the intrapulmonary arteries tend to be narrowed or obstructed by fibrosis, causing anastomosis to be impossible.[1]

In severe cases of haemoptysis or pulmonary haemorrhage such as our second case, selective embolization, lobectomy or even pneumonectomy should be considered. A study of 65 adults with IUAPA by Wang et al. showed that 83.3% of patients with haemoptysis who received selective embolization of collateral artery experienced recurrence. On the contrary, all seven patients who were followed up following pneumonectomy reported complete resolution of haemoptysis,[1] indicating pneumonectomy to be the superior treatment option in this cohort. Our patient has remained asymptomatic following a lobectomy.

The two cases we present demonstrated contrasting clinical presentation and severity of complications, respectively, resulting in an individualized management approach. The underlying reasons to the differing course is unclear since both patients are young male adults without significant smoking history and without significant comorbidity. Further studies are required to determine the risk factors for disease progression and development of complications. With adequate understanding of the disease, perhaps we will be able to establish more evidence‐based and uniformed management strategies.

IUAPA is a rare anatomical anomaly. A vast majority of patients remain asymptomatic to adulthood leading to delay in diagnosis which is often incidental. Patients have non‐specific symptoms, and a high index of suspicion is required to achieve timely diagnosis. We recommend physicians to consider possibility of IUAPA in those presenting with unexplained haemoptysis, recurrent chest infection or unexplained pulmonary hypertension. Management of IUAPA depends on the existing complications and the degree of pulmonary hypertension. Patients with IUAPA can have very different courses and no factors have been identified to predict the course they will take. Further studies are required to provide better risk stratification as well as elucidate the management of this condition.

All persons listed as authors have shown substantial contributions to: (i) the conception or design of the work, the acquisition, analysis or interpretation of data for the work; (ii) drafting the work or revising it critically for important intellectual content; and (iii) final approval of the version to be published.

None declared.

Data sharing is not applicable to this article as no new data were created or analyzed in this study.

The authors declare that appropriate written informed consent was obtained for the publication of this manuscript and accompanying images.