LECOM OMS-1 Embryology Development of the Heart Practice Exam

Tetralogy of Fallot stems from a failure of neural crest cells to properly contribute to the heart’s outflow tract, specifically the aorticopulmonary septum that divides the truncus arteriosus into the aorta and pulmonary trunk. Neural crest cells migrate into the outflow tract and form the spiral septum that ensures the correct alignment of the great arteries. When this neural crest–driven septation goes awry, the result is a membranous ventricular septal defect, an overriding aorta, and obstruction to the right ventricular outflow tract (pulmonary stenosis), which together produce the core features of TOF.

Endothelial cells and the endocardial cushions participate in septation in other contexts, and mesodermal cells give rise to many cardiac tissues, but the distinct conotruncal (outflow tract) defect seen in TOF is due to neural crest cell defects in outflow tract formation. Neural crest defects are also linked to DiGeorge syndrome, which further underscores the role of neural crest in this condition.