Isolated left-sided pulmonary artery agenesis with left lung hypoplasia: A report of two cases.

Unilateral absence of pulmonary artery or pulmonary artery agenesis (UAPA) is a rare congenital malformation that can present as an isolated lesion or in association with other cardiac anomalies. Though congenital, presentation in adults are also reported. Most common presentation in adults is of exercise intolerance. The developing lung on the affected side is hypoplastic. Diagnosis of UAPA is established by imaging methods like CT and MRI . There is no specific treatment for this condition. Treatment depends on patients symptomatology, presence of pulmonary hypertension and collateral circulation. Presence of pulmonary hypertension carries a bad prognosis. We present two adult patients with isolated left sided unilateral pulmonary artery agenesis with ipsilateral lung hypoplasia. The diagnosis was confirmed by CT chest and perfusion scan.

Introduction

Unilateral absence of pulmonary artery (UAPA) is a rare congenital cardiovascular anomaly due to malformation of the sixth aortic arch during embryogenesis. It can occur in isolation or in association with other anomalies. Although essentially a congenital anomaly, delayed presentation in adults are reported. We report two cases of isolated left pulmonary artery agenesis with ipsilateral lung hypoplasia in adults.

Case Report

A 65-year-old postmenopausal lady (Patient A) and a 32-year-old homemaker (Patient B) presented with history of exertional dyspnea of 1-year duration and 6-month duration, respectively. Both gave history of occasional cough with expectoration. They also gave history of recurrent respiratory infections. However, neither of them had a history of tuberculosis or associated comorbid illness like diabetes mellitus. On presentation, both were clinically stable and maintained normal saturation at room air. On examination, they had mild deviation of trachea to the left with reduced breath sounds in the left hemithorax and laterally placed apex beat. Their chest X-ray (CXR)/scanogram demonstrated shift of the mediastinal structures to the left and hyperlucent right lung [Figure 1]. A possibility of left lung collapse/left lung hypoplasia was considered. Contrast chest computed tomography (CT) showed hypoplastic left lung with bronchiectatic changes in the left lower lobe with herniation of right lung. Mediastinal structures were to the left [Figure 2]. Further on CT, Patient A had a rudimentary left pulmonary which was interrupted/abrupt termination within 1 cm of origin from the main pulmonary artery. The diameter of the left pulmonary artery and main pulmonary artery of Patient A are 7 and 23 mm, respectively. Patient B CT showed a left pulmonary artery of about 9 mm in diameter but was also abruptly terminated within 1 cm of origin from the main pulmonary artery. A possibility of left-sided pulmonary artery agenesis with left lung hypoplasia was suspected and both the patients underwent a perfusion scan which revealed no perfusion in the left lung with normal perfusion in the right [Figure 3]. Fiberoptic bronchoscopy showed narrowed segmental openings of the left lung. The left main bronchus and lobar bronchus were normal. Bronchial washings were collected from all the narrowed segments, but no organism was isolated. Patient B also had a more distally placed right upper lobe bronchus probably due to hyperinflation. Electrocardiogram of both the patients were normal. Echocardiography showed no associated anomalies or pulmonary hypertension (PHT) in both patients. A diagnosis of isolated left-sided pulmonary artery agenesis with left lung hypoplasia was made. Both the patients were counseled regarding their condition and are currently on regular follow-up.

Figure 1

Scanogram of both cases showing volume loss on left side with mediastinal shift to left side

Figure 2

Patient A – The red arrow shows normal right pulmonary artery (22.1 mm) and blue arrow shows rudimentary left pulmonary artery (9mm) in size. Patient B – The red arrow shows normal right pulmonary artery (26.7 mm) and blue arrow shows rudimentary left pulmonary artery (9mm) in size. Both measurements were made at just below bifurcation of trachea

Figure 3

Perfusion scan images of both cases: Technetium labeled macroaggregated albumin showing absent perfusion in the left lung

Discussion

UAPA is a rare congenital cardiovascular malformation that results principally due to failure of development of the ventral bud of the ipsilateral sixth aortic arch.[1] UAPA can occur in isolation or in association with other cardiovascular anomalies such as Fallot's tetralogy, coarctation of the aorta, ventricular septal defect, subvalvular aortic stenosis, transposition of the great arteries, and pulmonary atresia. The prevalence of isolated UAPA varies from 1 in 200,000 to 1 in 300,000.[23]

Chromosomal defects, vitamin A deficiency, intrauterine infections, and environmental factors have been implicated in the etiology of congenital pulmonary artery agenesis with pulmonary hypoplasia.[4] Pulmonary artery absence or agenesis is caused by the involution of the proximal sixth aortic arch and persistence of the connection of the intrapulmonary part of pulmonary artery to the distal sixth aortic arch.[3] Due to embryologic relationships, UAPA commonly occurs on the right side.[1] Left-sided UAPA is usually associated with other cardiovascular anomalies and is very rare to present in isolation. Both our patients had isolated left pulmonary artery agenesis. The distal intrapulmonary branches of the affected artery usually remain intact and receive collateral supply from bronchial, intercostal, internal mammary, subdiaphragmatic, subclavian, and even the coronary arteries.[56] As a result of diminished blood supply, the lung on the affected side is usually small and hypoplastic.

UAPA affects both sexes equally. UAPA can present from infancy till adult age with mean age of presentation being 14 years.[5] Left-sided UAPA is more common in infants, develop pulmonary hypertension (PHT) early and rarely survive to adulthood. Patients with right-sided involvement and isolated UAPA present have a late presentation and may survive to adult age. The majority of the adults are asymptomatic. Common symptoms include exercise intolerance (20%–40%), hemoptysis (20%), recurrent cough and expectoration and chest pain. Massive life-threatening hemoptysis is also reported.[578] PHT develops early in the disease process and is seen in up to 25% of patients at first presentation. The presence of PHT is a poor prognostic factor for long-term survival.[91011] Repeated infections also lead to bronchiectasis.[9] Hemoptysis in patients with UAPA is caused by excessive collateral circulation. Both our patients have bronchiectasis on the affected side.

Diagnosis of UAPA can be suspected from plain CXR films. On CXR, there may be cardiac and mediastinal displacement, the absence of the pulmonary artery shadow on the affected side, an ipsilateral elevation of the diaphragm, contralateral compensatory hyperinflation of the hemithorax, and herniation of lung across the midline.[12] All the features were present in our patients.

When CXR is suspicious, the diagnosis of UAPA can be confirmed by a contrast-enhanced CT (CECT) scan of the thorax, magnetic resonance imaging, or transthoracic echocardiography. On CT, hypoplastic pulmonary artery usually terminates within 1 cm of its expected origin from the pulmonary trunk. Other findings include intact peripheral branches of the pulmonary artery, variable collateral circulation, mosaic attenuation pattern, and bronchiectasis.

Pulmonary angiography (PA) is the gold standard investigation for the diagnosis of PA agenesis and estimation of collateral circulation. However, being an invasive procedure, it is better advised when a patient is planned for arterial embolization.[9] Echocardiography is required to rule out other associated cardiac anomalies and for assessment of PHT. Ventilation-perfusion scanning is not routinely indicated for the diagnosis of UAPA. Bronchoscopy is not useful in the diagnosis of UAPA. Cases with normal bronchoscopy have been reported.[7]

Differential diagnosis includes Swyer–James–Macleod syndrome, lobar atelectasis, postlobectomy status, and chronic pulmonary thromboembolism.[12] The overall mortality rate in UAPA is 7%.[35] Survival depends on the presence of PHT and pulmonary hemorrhage. Common causes of mortality include right heart failure, respiratory failure, massive hemoptysis, and high-altitude pulmonary edema.[311]

There is no specific treatment for UAPA. For asymptomatic patients, yearly echocardiography evaluation is advised to rule out PHT. Vasodilator therapy is advisable for patients with PHT. Revascularization of the peripheral branches of the affected pulmonary artery to the pulmonary hilum has been attempted successfully. Revascularization procedures yield better results in the pediatric patients.[310] For patients presenting with massive hemoptysis or with recurrent severe respiratory infections, surgical resection of the affected lung may be needed. Pulmonary artery embolization is an alternate option for patients not fit for surgery.

Conclusion

Although a congenital anomaly, UAPA can present in adults. Clinicians should consider this entity as one of the possible respiratory system differentials in patients presenting with recurrent pulmonary infections and exercise intolerance.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.