TRUNCUS ARTERIOSUS COMMUNIS (TAC) ASSOCIATED WITH MALFORMATIONS OF OTHER ORGAN SYSTEMS G. Sokolovska Malovceva, S. Duganovska, V. Janevska, S. Komina, A. Serafimov 1st Macedonian Congress of Pathology with International Participation, At Ohrid, Volume: Book of Abstracts, October, 12-16, 2011 Objective: To identify the rate and incidence of congenital defect Truncus arteriosus communis or TAC and its associations with malformations of other organ systems. Background Truncus arteriosus (TA) is an uncommon congenital cardiovascular anomaly that is characterized by a single arterial trunk arising from the normally formed ventricles by means of a single semilunar valve (ie, truncal valve). In addition, the pulmonary arteries originate from the common arterial trunk distal to the coronary arteries and proximal to the first brachiocephalic branch of the aortic arch. The common trunk typically straddles a defect in the outlet portion of the interventricular septum (ie, conal septum); however, in rare cases, it may originate almost completely from the right or left ventricle. In patients with a patent and normal caliber aortic arch, the ductus arteriosus is either absent or diminutive. Embryology The anomaly is thought to result from incomplete or failed septation of the embryonic truncus arteriosus, hence the persistence of the Latin term truncus arteriosus and its variants. Aortopulmonary and interventricular defects are believed to represent an abnormality of conotruncal septation. Because the common trunk originates from both the left and right ventricles, and pulmonary arteries arise directly from the common trunk, a ductus arteriosus is not required to support the fetal circulation. Accordingly, an inverse relationship between the caliber of the ductus arteriosus (derived from the sixth branchial arch) and that of the distal portion of the aortic arch (derived from the fourth branchial arch) is typically present. Although the hemodynamic consequences of a common arterial outflow may predispose to the development of the fourth or the sixth arch (but not both), anomalous development of the arch system is likely a fundamental aspect of the morphogenetic anomalies that produce truncus arteriosus.