Diagnosis: 
There are two diagnostic goals in LPAS - firstly to identify the retrotracheal aberrant LPA arising from the RPA and secondly to establish the degree of airway compromise and stenosis and if they are complete tracheal rings. The former can be reliably ascertained with echocardiography showing the main pulmonary artery extending directly to the right pulmonary artery, and the left pulmonary artery arising from the right pulmonary artery (figure 4). Other intracardiac lesions may also be identified by echocardiography.