Pulmonary Artery Sling

Pulmonary artery sling is a rare defect created by anomalous origin of the left pulmonary artery from the posterior aspect of the right pulmonary artery. The anomalous left pulmonary artery courses over the right mainstem bronchus and then from right to left, posterior to the trachea or carina and anterior to the esophagus, to reach the hilum of the left lung. This compresses the lower trachea and right mainstem bronchus, producing upper airway symptoms. Compression caused by the sling can produce obstructive emphysema, atelectasis of the right and left lungs, or both. Thus, early recognition and diagnosis of pulmonary artery sling, and of stridor in a young infant, are crucial.

An example of pulmonary artery sling is shown in the illustration below.

Associated tracheobronchial abnormalities may occur, especially complete tracheal rings and tracheomalacia. Hypoplasia and stenosis of tracheal segments occur and can potentiate the airway obstruction. Congenital heart defects are found in 50% of pulmonary artery sling cases, most commonly atrial septal defect, patent ductus arteriosus, ventricular septal defect, and left superior vena cava.

Other organ system abnormalities may occur. These include imperforate anus, Hirschsprung disease, biliary atresia, and genitourinary defects. Abnormalities of ovaries, vertebrae, thyroid gland, and pulmonary parenchyma have been reported.

The specific etiology of the pulmonary artery sling is unknown.

As the left pulmonary artery passes posteriorly and caudally to the right main-stem bronchus and to the left behind the trachea, tracheal and bronchial compression occurs. The course of the anomalous left pulmonary artery to the right of the trachea produces deviation of the lower trachea to the left with resulting compression of the right mainstem bronchus and lower trachea. This results in airway obstruction that primarily affects the right lung, although compression of the lower trachea and left mainstem bronchus can result in bilateral obstruction.

Other abnormalities in the arterial supply to one or both lungs can be seen in association with this abnormality. On occasion, the anomalous pulmonary artery may supply only the left upper lobe with normal pulmonary arterial supply to the left lower lobe. In addition, partial anomalous supply of the right upper lobe of the lung from the anomalous left pulmonary artery has been described.

Owing to the relative rarity of this condition, the true incidence and frequency of pulmonary artery sling in the United States and globally is not known. A retrospective study showed a hospital-based prevalence of 0.14% for left pulmonary artery sling among Chinese patients with congenital heart disease.[1]

Race-, sex-, and age-related demographics

No racial or sex predilection is known.

Symptoms, including respiratory distress manifested by stridor, recurrent pneumonia, wheezing, and cyanosis, typically occur within the first month of life. Dysphagia is rare, but obstructive apnea may occur. These patients tend to be more symptomatic and to present even earlier than those with a vascular ring due to a double aortic arch.

With early diagnosis and surgical correction, the prognosis is good.[2]  Surgical mortality is increased by coexisting tracheal or bronchial stenosis.

Surgical survivors may be free of significant symptoms at long-term follow-up; however, because many demonstrate some persistent airway obstruction, they should be closely observed for both airway as well as pulmonary artery complications.

Morbidity/mortality

In severely affected infants, death can occur in the early months of life. Survival is unlikely without surgical intervention. Mortality varies and has been reported to be relatively high in previous studies. The major contributor to postoperative mortality is the high frequency of bronchial and tracheal abnormalities in this group of patients. Early, aggressive intervention may minimize the mortality caused by these associated lesions.[3]

Morbidity includes frequent episodes of stridor and respiratory distress with or without wheezing and cyanosis. Recurrent pneumonia can occur.

Complications

Because of associated tracheomalacia, tracheal stenosis, and/or bronchial stenosis, postoperative symptoms of airway obstruction are common. Left pulmonary artery stenosis may occur and can be progressive.

Parents should be educated about issues with regard to airway obstruction and tracheobronchial toilet. Patients in the immediate postoperative period still may be at risk during respiratory illnesses because of increased secretions. Over time, with healing and improvement of the tracheomalacia/tracheal stenosis, these symptoms should improve.

No preventive measures are known.

In patients with pulmonary artery sling, the history is predictable and usually not subtle. Most infants are affected within the first few weeks of life and present with stridor, respiratory distress, cyanosis, wheezing, and/or pneumonia.

Physical examination demonstrates respiratory distress with stridor, dyspnea, and wheezing. When tracheal obstruction is present, the infant may have constant retractions and tachypnea. If a congenital heart defect is associated, its typical physical findings can be identified.

The lower trachea is deviated to the left and may appear compressed on its right side. Hyperinflation of the right lung may be seen because of impingement on and compression of the right main stem bronchus. The left lung also may appear hyperinflated because of obstruction at the level of the carina and the left main stem bronchus. In patients with severe obstruction, atelectasis of a single lung or single lobe may be observed. The lateral view may reveal a density anterior to the esophagus and posterior to the trachea just above the carina. This is the left pulmonary artery viewed on end.

The barium swallow is the diagnostic procedure of choice. An anterior indentation of the esophagus on the lateral projection is diagnostic of pulmonary artery sling. The esophagus is usually displaced to the right in the frontal projection and demonstrates an oblique impression immediately posterior to the carina.

In the usual coronal-plane suprasternal-notch images, absence of normal bifurcation of the main pulmonary artery into right and left pulmonary arteries is visible. The left pulmonary artery appears to be absent. However, examination of the right pulmonary artery reveals the left pulmonary artery arising from its posterior surface. The left pulmonary artery can be followed posterior to the trachea and anterior to the esophagus. It passes anterior to the descending aorta and enters the hilum of the left lung. Echocardiography also reveals any associated congenital heart defects.

Magnetic resonance imaging (MRI) or magnetic resonance angiography (MRA), computed tomography (CT) scanning, or a combination of these imaging modalities can be helpful in delineating the details of the anatomy,[4] as well as in three-dimensional reconstruction of the anatomy of the sling as it relates to the airway anatomy.

Bronchoscopy is generally not recommended in patients with pulmonary artery sling. If performed, tracheal compression is noted, and accompanying tracheomalacia, tracheal stenosis, or both is common.[5] Some recommend bronchoscopic evaluation of selected surgical candidates because surgical reconstruction of the trachea or bronchi may be necessary if the airway compromise is severe.

The diagnosis can usually be noninvasively established. Pulmonary artery angiography may be advisable to delineate anatomic details prior to surgical correction.[6, 7] This permits diagnosis of variations in right and left pulmonary artery anatomy that may not be apparent from noninvasive studies and that can alter the surgical approach. Origin and course of the anomalous left pulmonary artery is best revealed by contrast injection into the main pulmonary artery filming in an oblique view with steep cranial angulation of 60º -70º.

In patients with pulmonary artery sling, medical care is supportive until the patient can undergo definitive surgical correction. Inpatient care in patients with pulmonary artery sling may be required for symptoms of airway obstruction and/or pneumonia.

Hypoxemia and respiratory distress should be treated with supplemental oxygen and endotracheal (ET) intubation if indicated. Treat pneumonia with appropriate antibiotics.

Stabilize the patient and make arrangements for surgery as soon as possible. Infants without airway obstruction and with minimal symptoms may not require surgical intervention. However, this scenario is the rare exception.

After surgical repair, these symptoms of airway obstruction and/or pneumonia may persist, although they should improve over time.

Consultations

Obtain consultations with the following specialists:

• Pediatric cardiologist

• Cardiovascular surgeon experienced in congenital heart defect surgery

• Radiologist

Transfer

Patients hospitalized with significant stridor, in whom a vascular ring or pulmonary artery sling is suspected, should be transferred to a facility that can provide pediatric cardiology and pediatric cardiovascular surgery services.

Diet and activity

No specific dietary considerations are needed.

Normal activity is indicated after surgical repair unless significant airway obstruction persists.

Survival of symptomatic infants with pulmonary artery sling is unlikely without early surgical intervention. In 1954, Potts and Hollinger reported the first description of surgical repair of this lesion.[8] Surgery involves division of the anomalous left pulmonary artery and reanastomosis to the main pulmonary artery anterior to the trachea. Although this can be performed from a left thoracotomy, approach from a midline sternotomy with cardiopulmonary bypass may offer more control. The findings from one study, which presented a large series of successful patient management experiences, emphasize the advantage of cardiopulmonary bypass as the treatment of choice.[9]

Mortality varies and has been reported to be relatively high in previous studies. The major contributor to postoperative mortality is the high frequency of bronchial and tracheal abnormalities in this group of patients. Early, aggressive intervention may minimize the mortality caused by these associated lesions. If airway stenosis is severe, patients may require surgical reconstruction of the obstructed bronchi or trachea at the time of reimplantation of the anomalous left pulmonary artery. For example, tracheal stenosis associated with pulmonary artery sling is often repaired using sling tracheoplasty.[9] See the video below.

Surgical survivors are usually free of significant symptoms at long-term follow-up. However, some degree of airway obstruction may persist in as many as 45% of patients.

Follow-up

Close follow-up care after surgery is required, particularly monitoring for persistent airway obstruction.

Although airway symptoms should improve, follow patients closely, especially during times of upper respiratory infections.

Similarly, monitor this group of patients closely for the possibility of left pulmonary artery stenosis after reimplantation of the vessel. This can be noninvasively assessed with echocardiography but rarely may require follow-up pulmonary artery angiography.

No specific medications directly influence this abnormality. Patients with pneumonia require management with appropriate antibiotics.