Situs ambiguus

Cardiomegaly and pulmonary plethora implies a large left to right shunt from a congenital defect. Note that the stomach bubble is under the right diaphagm which signifies liver on left as is the apex of the heart. This has several names: isolated levocardia or situs ambiguus. Its importance is that it is associated with certain intracardiac lesions such as atrioventricular defects and single atrium. In addition there is evidence of venacaval abnormalities shown by the bulge on the upper right mediastinal border in the region of superior vena cava/right atrial junction which is the dilated inferior vena cava end on joining at that point instead of lower right atrium. There is another bulge on the left upper border of the mediastinum where the pulmonary artery is expected and in the region of straight shadow of probable left superior vena cava , which is a left hemiazygos (like a left inferior vena cava joining from the abdomen) and this forms the left bulge. Anomalies of systemic venous drainage are common with single atrium. The diagnosis of left isomerism would be made were the bronchi visible as these vena caval anomalies are associated with left isomerism.