Pulmonary artery sling
An anomalous origin of the left pulmonary artery, such that it arises from the posterior aspect of the right pulmonary artery and passes between the trachea and esophagus to reach the left hilum. [ http://www.ncbi.nlm.nih.gov/pubmed/16549603 http://www.ncbi.nlm.nih.gov/pubmed/18458183 ]