Persistent truncus arteriosus is an anomaly in which a single vessel (truncus) arises from both ventricles through a VSD. Systemic, pulmonary and coronary circulation originate from the truncus, which is provided with a common valve. Four types of truncus arteriosus may be distinguished according to the degree of blood flow to the lung. In type I, the common type, a rudimentary separate pulmonary trunk gives origin to the left and right pulmonary arteries. In type II a separate pulmonary trunk is absent; the left and the right pulmonary arteries originate from the left side of the common trunk. In type III the left and right pulmonary arteries originate from the left and right side of the common trunk, respectively. In the so-called type IV the pulmonary arteries are completely absent; the pulmonary circulation is supplied by systemic collateral arteries arising from the descending aorta.
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