Pulmonary artery sling and tracheal stenosis

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Anatomy and pathophysiology

Pulmonary artery sling occurs when there is failure of development of the left sixth aortic arch during gestation. When this occurs, the left pulmonary artery arises as a branch from the right pulmonary artery rather than as a branch from the main pulmonary artery. The result is a left pulmonary artery that courses posteriorly between the trachea and esophagus before reaching the hilum of the left lung. Symptoms are usually due to tracheal compression and include wheezing and stridor. Presentation usually occurs in infancy.

Tracheal stenosis is commonly associated with pulmonary artery sling, with complete tracheal rings occurring in 25% to 50% of cases. Complete tracheal rings are characterized by full cartilaginous rings around the trachea, rather than “C” shaped tracheal cartilages with a membranous posterior portion seen in the normal trachea. A long segment of complete tracheal rings, sometimes referred to as “stovepipe” trachea, can result in severe stenosis and a narrow tracheal lumen. Classically, the diagnosis of pulmonary artery sling was made by barium esophagram, in which a pulsatile anterior indentation of the esophagus is observed. Today diagnosis is made by echocardiography, magnetic resonance imaging, and spiral computed tomography. Magnetic resonance imaging and CT scan permit complete delineation of the vascular anatomy and are helpful in determining the presence or absence of tracheal stenosis. If tracheal stenosis is suspected, bronchoscopy should be performed at the time of surgery to determine the length and degree of tracheal involvement.

Surgical technique

Repair of pulmonary artery sling is accomplished through a median sternotomy. If there are no additional intracardiac defects or significant tracheal narrowing, repair can be accomplished without the use of cardiopulmonary bypass. Using partial occlusion clamps, the left pulmonary artery is detached from the right pulmonary artery, the origin oversewn, and the left pulmonary artery implanted end-to-side into the main pulmonary artery. If there are associated intracardiac defects or if significant tracheal stenosis is present, then cardiopulmonary bypass is used. When performed with cardiopulmonary bypass, aortic cross-clamping is not required unless repair of intracardiac defects is necessary. Tracheal reconstruction is performed when moderate to severe tracheal stenosis is present and the patient is symptomatic. Two techniques for intervention on the trachea are generally used: resection with end- to-end anastomosis and slide tracheoplasty. For both techniques, the trachea is mobilized posteriorly and anteriorly, keeping the lateral blood supply intact. With short segment stenosis, the narrowed area can be excised and the trachea reapproximated using absorbable suture. For more extensive tracheal steno- sis, a slide tracheoplasty is preferred. The trachea is transected at the point of maximal stenosis. The trachea is then incised along its length above and below in such a way as to allow overlapping of the segments. This overlapping or slide technique maximizes the caliber of the trachea while minimizing the tension on the reconstruction. Reconstruction is accomplished with absorbable monofilament sutures. Following repair, the patient is reintubated and separated from cardiopulmonary bypass. Bronchoscopic visualization of the tracheal lumen is performed to assess adequacy of repair.

Postoperative considerations

The postoperative course following repair of isolated pulmonary artery sling is usually uncomplicated. When associated defects are addressed, the post- operative course for those lesions would apply. Generally, the presence of symptomatic preoperative tracheal stenosis is predictive of a longer postoperative course, and airway issues dominate the picture. When tracheal reconstruction is performed, frequent assessment of the airway with bronchoscopy may be necessary.

Invasive monitors used postoperatively include arterial and central venous catheters. Non-invasive monitors might include NIRS (near-infrared spectroscopy) probes to assess adequacy of regional and global perfusion and traditional pulse oximetry. Vasoactive infusions might include milrinone and occasionally low-dose epinephrine. Cardiac arrhythmias are rare, persistent postoperative bleeding is uncommon, and cardiovascular recovery is usually uncomplicated. Arterial and central venous pressures and systemic saturations should be normal. Hospital stay following uncomplicated pulmonary sling repair averages 3 days to 1 week. Hospital stay will likely be longer following repair of tracheal stenosis and is predicted by the extent of the stenosis and the severity of preoperative symptoms.