The retrotracheal left pulmonary artery: A rare vascular malformation

Abstract

The retrotracheal left pulmonary artery, also known as “left pulmonary artery sling,” is a rare vascular malformation in which the left pulmonary artery (LPA) arises from the posterior aspect of the right pulmonary artery (RPA) and reaches the left pulmonary hilum by passing between the trachea and the esophagus, giving rise to the appearance of a sling, hence the name “sling.” This vascular anomaly can be associated with other cardiac malformations or abnormalities of the tracheobronchial tree.We present the case of a 4-month-old female infant who presented with laryngeal stridor. She underwent a chest X-ray, which was normal, but thoracic CT angiography revealed an aberrant LPA originating from RPA with a retrotracheal course. This case underscores the critical role of imaging in confirming the diagnosis and guiding patient management.

Introduction

The retrotracheal left pulmonary artery, also known as “left pulmonary artery sling,” is a rare vascular anomaly causing respiratory distress in which the LPA arises from the RPA and passes posteriorly [1].

Tracheal symptoms such as stridor, wheezing, recurrent pneumonia, and respiratory distress may present during the first year of life [2].

This vascular anomaly can be associated with other cardiac malformations or abnormalities of the tracheobronchial tree.

Chest radiography, Chest CT angiography and echocardiography play a fundamental role in the diagnosis and preoperative assessment of this malformation.

Early surgical repair can reduce morbidity and mortality.

Herein, we report a case of left pulmonary artery sling that was presented with chronic stridor.

Case report

We present the case of a 4-month-old female infant, with a history of consanguinity, exhibiting fatigue during feeding accompanied by laryngeal stridor.

On physical examination, the infant was afebrile. Her weight was below the 3rd percentile. Vital signs were within normal limits. There were no abnormalities in the cardiovascular or respiratory assessments. The abdomen was soft and nontender, and neurological reflexes were age-appropriate.

A chest X-ray was initially performed, which revealed no abnormalities. Blood laboratory results were within normal limits.

A chest CT angiography was performed, which reported an aberrant LPA originating from the RPA with a retrotracheal course. The LPA was 1.25 times the size of the RPA, There were no abnormalities of the tracheobronchial tree (Fig. 1, Fig. 2, Fig. 3).

Fig. 1.

Scan topogram showing no abnormalities.

Fig. 2.

Axial CT angiography showing the left pulmonary artery (LPA) from the posterior aspect of the right pulmonary artery (RPA), main pulmonary artery (MPA),trachea (asterisk).

Fig. 3.

Coronal Chest CT scan. (A, B and C) Lung window, 3D and MinIP reconstructions of the airway and lungs, revealing no abnormalities of the tracheobronchial tree.

Transthoracic echocardiography did not demonstrate cardiac malformations except for the persistence of a small left superior vena cava.

The patient was referred to a specialized center abroad for surgical management. However, the family declined the referral due to financial constraints. The infant was scheduled for a follow-up with a CT angiography and transthoracic echocardiography in 6 months.

Discussion

The retrotracheal left pulmonary artery is a rare condition that can cause respiratory distress, with nonspecific symptoms such as cough, stridor, wheezing, and dysphagia [3].The exact prevalence is difficult to determine due to the unknown number of asymptomatic cases [4].

Compared to other vascular rings, tracheobronchial stenosis in left pulmonary artery sling (LPAS) is primarily anatomical, resulting from congenital tracheal stenosis, rather than being dynamic or associated with tracheobronchomalacia [5].

The embryology of retrotracheal left pulmonary artery has not been fully clarified, with various theories proposed in the literature. One theory suggests that abnormal fusion of the left lung bud plexus with the right sixth branchial arch, instead of the left one, during the vascular supply shift at 32 days of embryonic development, can lead to the formation of left pulmonary artery sling [6].

In retrotracheal left pulmonary artery cases, tracheal stenosis often begins at a higher level of the trachea and extends to the carina, rather than being localized to the area where the left pulmonary artery encircles the trachea. This is attributed to the “squeezing and milking” hypothesis, which posits that as the heart descends along with the carina, it exerts compressive forces on the trachea [7].

In 1988, Wells introduced a classification system for left pulmonary artery slings, distinguishing between type I and type II based on the sling's location relative to the carina. This classification is further divided into subtypes A and B depending on the presence or absence of a bronchus for the right upper lobe. Specifically, type I lesions are characterized by the trachea being positioned at the level of T4-T5, while type II lesions have the trachea at the level of T6-T7 [1].

In our case, the tracheal compression caused by the left pulmonary artery occurs at the tracheal bifurcation, indicating a type IA.

Positive diagnosis relies on imaging. Chest radiography is typically the initial diagnostic step in cases of respiratory symptoms. Its primary purpose is to rule out other conditions that might present with similar clinical features. Thoracic CT angiography is the preferred diagnostic test for confirming the diagnosis of a pulmonary artery sling. It provides crucial information for the surgical team, including details about the type of anomaly and the presence of any additional malformations. This comprehensive imaging helps to optimize patient management and enhance the prognosis.

The optimal treatment for a pulmonary artery sling is surgical repair. This typically involves a sternotomy through a midline incision, followed by cardiopulmonary bypass, detachment of the left pulmonary artery (LPA), and anastomosis between the LPA and the main pulmonary artery, as performed in our patient [8]. Tracheoplasty should be considered if there is symptomatic tracheal stenosis, as in the current case. The clinical outcome after surgery depends on the presence of other cardiac malformations and tracheal anomalies [9].

Conclusion

The retrotracheal left pulmonary artery is an uncommon vascular anomaly. CT angiography aids in accurate diagnosis and the planning of effective treatment strategies. The treatment relies on surgery, and the outcomes depend on the presence of other cardiac malformations and tracheal anomalies.

Patient consent

Written informed consent was obtained from the legal authorized representative of the patient for the publication of this case report.