Abnormal Migration of the Conotruncal Septum 1

Question

Vignette: A 2-day old newborn boy is observed to have cyanosis and difficulty feeding. Physical examination reveals a single loud second heart sound and a systolic ejection murmur. An echocardiogram is performed and shows a large ventricular septal defect, overriding aorta, right ventricular outflow tract obstruction, and right ventricular hypertrophy. This condition is the result of abnormal migration of which embryonic structure?

Choices

A. Endocardial cushions

B. Neural crest cells

C. Sinus venosus

D. Septum secundum

E. Bulbus cordis

Answer

B. Neural crest cells

Explanation

This vignette describes a case of Tetralogy of Fallot, the most common cyanotic congenital heart disease. The four features include ventricular septal defect, overriding aorta, right ventricular outflow tract obstruction (pulmonary stenosis), and right ventricular hypertrophy. The embryological basis for this condition is the anterior and cephalad displacement of the conotruncal septum, which is formed from neural crest cells and the endocardial cushions. Therefore, abnormal migration of neural crest cells during embryogenesis can result in this condition. While the endocardial cushions (choice A) do contribute to the formation of the conotruncal septum, they primarily contribute to the formation of the atrioventricular septum and valves. The sinus venosus (choice C), septum secundum (choice D), and bulbus cordis (choice E) do contribute to heart development, but they are not directly related to the pathogenesis of Tetralogy of Fallot.