Truncus Arteriosus

Michael P. D'Alessandro, M.D.
Peer Review Status: Internally Peer Reviewed

Etiology/Pathophysiology:
Due to a failure of division of the embryonic truncus arteriosus into the aorta and pulmonary artery. A single great artery leaves the heart and gives rise to the coronary, pulmonary, and systemic arterial circulation. The truncus stradles a high VSD and receives outflow from both ventricles. A truncal valve has 2-6 cusps, and usually is incompetent. Truncus is classified by the origin of the pulmonary artery:

• Type I has a single main pulmonary artery that originates from the lateral wall of the truncus. This is the most common type.
• Type II has a separate right and left pulmonary artery arising from the posterior truncal wall.
• Type III has the pulmonary artery arising from the lateral wall of the truncal vessel.
• Type IV has absent pulmonary arteries and is rare. It is probably a severe TOF with pulmonary atresia and large bronchial collaterals and is often called a pseudotruncus.

Pathology:
Not applicable

Imaging Findings:
For Type I truncus and Type II and Type III without pulmonary stenosis, increased pulmonary vasculature and cardiomegaly is seen due to biventricular and left atrial enlargement due to the left to right shunt and insufficiency of the truncus valve. It can resemble TGA on CXR, but note that 30% of truncus have a right arch while only 5% of TGA do.

DDX:

• Not applicable

References:
See References Chapter.

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