A rare case of ‘ring-sling complex’ in a symptomatic adult patient: A left pulmonary artery sling with complete tracheal rings

Abstract

Pulmonary artery sling (PAS) is a rare congenital condition, in which the left pulmonary artery (LPA) originates from the right pulmonary artery instead of the main pulmonary artery. It courses between the oesophagus and the trachea, forming a sling and causes compression of both structures. We report a very rare case of a symptomatic adult patient with PAS and a coexisting tracheal anomaly with complete tracheal rings, referred to as a ‘ring-sling complex’.

Introduction

Pulmonary artery sling (PAS) is a rare congenital heart abnormality, in which the left pulmonary artery (LPA) originates from the right pulmonary artery (RPA). PAS courses between the oesophagus and the trachea, forming a sling and causes compression of both structures. (Figure 1) The estimated incidence is at 59 per million live births, and about 90% of the cases are diagnosed within the first year of life. ¹ Symptomatic infants have high mortality rates without surgical interventions. Adult cases are very rare that very few cases are reported worldwide. PAS is commonly associated cardiovascular and tracheobronchial anomalies. We here report a very rare symptomatic adult case with a ‘ring-sling complex’, which combines PAS and a coexisting tracheal anomaly with complete tracheal rings.

Figure 1.

(A) A left pulmonary artery sling; (B) repaired left pulmonary artery sling. MPA indicates main pulmonary artery; LPA, left pulmonary artery; RPA, right pulmonary artery.

Case report

A 25-year-old female with a historical diagnosis of asthma was referred to our department after an episode of difficult intubation for a routine gynaecological procedure. She reported several years’ history of ongoing exertional dyspnoea and incomplete reversibility of airway obstruction despite optimal treatment for asthma and the absence of smoking history. Forced expiratory volume in the first second (FEV1) was 2.81 L (53% of predicted value) and forced vital capacity (FVC) was 3.23 L (65% of predicted value). A computed tomography (CT) angiogram showed a left PAS, and a rigid bronchoscopy confirmed an abnormal anatomy with complete tracheal rings without posterior membranous portion and significant short distal tracheal stenosis. A transoesophageal echocardiogram (TOE) showed no cardiac abnormalities. The patient underwent surgical reconstruction of the left PAS to re-implant the LPA to the main pulmonary trunk and resection of the distal trachea via a median sternotomy and the use of extracorporeal circulation. A bovine pericardium tubular graft (21 mm Biointegral with a removed valve) was anastomosed onto the LPA and the stenotic distal trachea was resected for the length of 4 rings just above the carina. The patient was successfully extubated on the day. Day 1 post-operatively, the patient desaturated down to 77% requiring oxygen support in a high dependency unit (HDU) and a CT suggested a kink in the PA graft with a left basal perfusion defect (Figure 2A). Day 2 post-operatively, an emergency operation was performed via a fifth intercostal space (ICS) thoracotomy. The previous PA conduit was found to be flattened, so it was divided and a 14 mm PTFE GORE-TEX reinforced graft was anastomosed end to end to the left distal PA (Figure 2B). The patient then made a good recovery, extubated on day 2 and discharged on day 8 post-operatively, but reported dysphonia possibly from left vocal palsy. At the 3-month follow-up, the patient was doing well, but dysphonia did not resolve and underwent successful vocal cord injection.

Figure 2.

A left sagittal view of three-dimensional computed tomography (3D ct). (A) A kink in the left pulmonary artery graft (white arrow); (B) a new placement of the left pulmonary artery GORE-TEX reinforced graft.

Discussion

PAS is a rare congenital cardiovascular condition, in which LPA originates from the RPA and passes between the trachea and the oesophagus. Embryologically, normal proximal pulmonary arteries, formed the sixth aortic arch, join with the distal pulmonary arteries, which arise from the respective lung buds. PAS results from the lack of normal development of the left sixth aortic arch, which leads to the left post-brachial vessels failing to connect with the left sixth branchial arch, and the connection between the right sixth branchial arch and the trachea forms. ² Most patients present in the early infancy and typically present with signs of respiratory distress due to tracheal compression or stenosis, which can be life-threatening. A classification system divides PAS into two types: type 1 without complete tracheal rings and type 2 with complete tracheal ring, referred to as ‘ring-sling complex’. ³

In contrast to this dire prognosis in children, adult cases are much rarer and are most often asymptomatic. Clinical presentations can be non-specific and variable, so reaching the definitive diagnosis may be more challenging. We believe that the diagnosis for our patient was delayed until adulthood due to lack of serious intracardiac abnormalities or the relatively patent lower trachea. All paediatric patients with the diagnosis of PAS should undergo surgical intervention, but surgery in adults is very rare. ⁴ In contrast to infant surgery, the native LPA cannot be reanastomosed. In the choice of conduit, we learnt that it should be as short as possible, and the more rigid PTFE GORE-TEX reinforced graft was preferred to the softer pericardial material. The secondary left thoracotomy was helpful for better access, but the PTFE graft could have been inserted primarily via a sternotomy. Current literature reports that only two symptomatic adult patients underwent surgical treatment with satisfactory results, improving severe symptoms arising from tracheal compression. ⁵ Due to low incidence of PAS in adults, there is no reliable statistical data for long-term survival.

Conclusion

Due to the small number of cases worldwide, we currently do not have established a management strategy for both paediatric and adult patients with PAS. We need to acknowledge that case reports have a significant role in the elucidation of the rare conditions, and therefore further publications will be a cornerstone for future research.