Discussion

Pulmonary artery sling by definition is an aberrant left pulmonary artery that originates from the right pulmonary artery and passes leftwards around the right bronchus and between the lower trachea and oesophagus into the left hilum. Embryologically, the distal branch pulmonary arteries arise from the capillaries of their lung buds. Then, each branch pulmonary artery is joined with the ipsilateral sixth aortic arch. If this process fails, a pulmonary sling is formed when the connection between the left pulmonary artery – from the left lung bud – and the right sixth aortic arch – right pulmonary artery – occurs behind the trachea. This might happen as a consequence of the loss of the left sixth aortic arch. The presence of a right aortic arch and an aberrant left subclavian artery are the results of disappearance of the left fourth aortic arch, persistence of the right fourth aortic arch, which becomes the right arch, and loss of the left sixth aortic arch, except for the ductus arteriosus.Reference Lee, Printz, Hegde, Vargas and Sun ¹ When the aforementioned developmental processes occur simultaneously, a pulmonary sling and a vascular ring may coexist. In all, 50–65% of left pulmonary artery slings are associated with complete tracheal rings, and of these 70–80% are associated with tracheal stenosis.Reference Fiore, Brown, Weber and Turrentine ^{2 ,} Reference Backer, Russell, Kaushal, Rastatter, Rigsby and Holinger ³ The patient described above has complete tracheal rings with no evidence of intrinsic stenosis. For that reason, we elected not to perform any kind of tracheoplasty manoeuvres. In our institution, the presence of complete tracheal rings per se does not necessitate tracheal intervention. On the other hand, an associated intrinsic stenosis would definitely require an intervention in the form of a sliding tracheoplasty, which is our method of choice in dealing with tracheal stenosis. Three main imaging modalities are used for the diagnosis and surgical planning, and these include echocardiogram, CT scan, and bronchoscopy. Intracardiac lesions, the course of the anomalous artery, the extent, and significance of tracheal stenosis must all be clearly delineated before surgery.

Potts et al performed the first surgical repair of a pulmonary artery sling in a 5-month-old patient through a right thoracotomy.Reference Potts, Holinger and Rosenblum ⁴ Since then, surgical technique has evolved into using cardiopulmonary bypass. The ideal approach for left pulmonary sling repair is through a median sternotomy on cardiopulmonary bypass as opposed to thoracotomy. This would reduce the incidence of postoperative pulmonary stenosis by providing adequate exposure for the proper orientation of the vessel. Nevertheless, there is still more than 50% risk of future stenosis of the re-implanted branched pulmonary artery in the first few months after surgery.Reference Wu, Downing and Mascio ⁵ To overcome this potential problem and the mild hypoplasia of the native vessel, we elected to augment the re-implanted left pulmonary artery with pericardium. In contrast to slings, the ideal approach for most vascular rings is through thoracotomy. Resecting Kommerell’s diverticulum and re-implanting the aberrant subclavian artery via median sternotomy incision is technically challenging. We elected to avoid doing that for two reasons. First, we had an adequate tissue recoil that we believed to be sufficient in relieving the vascular ring after dividing the ligamentum arteriosum. Second, the external tracheal compression was relieved without resecting the diverticulum. A similar case has been reported in literature that involved the prenatal diagnosis of an left pulmonary artery sling, as well as a right aortic arch with a left ductus arteriosus without Kommerell’s diverticulum resulting in a vascular ring. The infant underwent sliding tracheoplasty, left pulmonary artery re-implantation, and division of the ligamentum arteriosum on day of life 11 and he had residual postoperative left pulmonary artery and tracheal stenosis.Reference Jeong, Han, Hahn and Lee ⁶ Another case showed the association between pulmonary artery sling with right aortic arch and aberrant left subclavian artery with no ligamentum arteriosum. The child underwent an uneventful left pulmonary artery re-implantation. To our knowledge, this is the first report of a child with VACTERL association that has both an left pulmonary artery sling and a vascular ring.