Review Question - QID 101923

Transposition of the great arteries (TGA), a cause of congenital cyanosis, is due to failure of aorticopulmonary septum to spiral. The fetal aorticopulmonary septum normally spirals during septation of the truncus arteriosus, and errors in this process lead to the aorta emerging from the right ventricle and the pulmonary artery emerging from the left ventricle.

Without an alternate route for circulation of oxygenated blood into the aorta and systemic circulation, infants with this condition will die at birth. Infants who survive postnatally thus depend on either intracardiac (ventricular septal defects and/or patent foramen ovales) or extracardiac (patent ductus arteriosus or bronchopulmonary collaterals) shunts in order to supply the systemic circulation with oxygenated blood. At present, fetal diagnosis of TGA is challenging, and most cases are diagnosed after birth by echocardiography. Surgical correction is required.

Incorrect Answers:
Answer 1: Ventricular septal defects result most commonly from defects in fusion of the membranous ventricular septum.
Answer 3: One theory about the pathogenesis of aortic coarctation says that extension of ductal tissue into the aorta creates a thickened segment that is pulled tight when the ductus arteriosus closes.
Answer 4: Omphalocoele is a midline abdominal wall defect wherein abdominal viscera fail to reenter the abdomen, with organs located in a sac outside the body.
Answer 5: Patent foramen ovale results from failure of fusion of the atrial septum primum and secondum. This typically results in left-to-right shunting, and would not result in early cyanosis.