The lateral view shows that the anterior clear space behind the sternum is occupied above a poion of the lower one-third of the cardiac shadow. The truncus of the right pulmonary aery seen in front of the trachea is very large and the left main pulmonary aery coursing over the left upper lobe bronchus is greater than 16 mm. These findings are consistent with pulmonary aerial hypeension. The chest x-ray shows large pulmonary aeries, and this, coupled with the clinical scenario, is consistent with primary pulmonary hypeension (PPH). As mentioned in the general discussion, this entity is due to an unknown cause. The physical sign most likely to be present would be a loud P2, and right hea catheterization would confirm the high pulmonary aery (PA) pressures. Patients with PPH may give a history of syncopal episodes. A loud A2 is heard in systemic hypeension, and rib notching is classically seen on the x-ray in coarctation of the aoa. Right arm swelling is seen with either a localized vascular or lymphatic obstruction such as postradiation, malignancy, or superior vena cava syndrome. This patient does not exhibit any of these signs. Since the hilar shadows are of vascular nature, mediastinoscopy or bronchoscopy would not be indicated and in fact may be dangerous if PA pressures are very high.