Figure 3 : Landmarks for an upper partial median sternotomy. The incision is carried through the midline of the sternum generally to the 2nd intercostal space. Critical for exposure is an adequate extension of the neck with a good size shoulder roll, especially in infants.
A total thymectomy is then performed taking care not to injure the phrenic nerves bilaterally. This is critical as the thymus is often large and acts as a space occupying lesion. It is preferable not to enter the pleural spaces. The innominate vein is then mobilized and retracted superiorly. The innominate artery is then dissected only on its anterior aspect and the pericardial reflection at its base on the aortic arch is opened in a limited fashion. Again, it is critical not to circumferentially dissect the innominate artery as this will lead to a loss of the natural adhesion between it and the anterior surface of the trachea. A pretracheal plane is thus not developed. This is important. As the innominate artery is pulled anteriorly towards the sternum (given the space after the thymectomy), besides relieving the tracheal compression, it helps support the associated tracheomalacia by suspending the anterior wall of the trachea indirectly to the sternum (Figure 4 ).