Embryology · Heart and vessels
Persistent truncus arteriosus !
- Malformation
A single vessel leaves the heart instead of two, because the wall that separates the aorta from the pulmonary artery never formed.
Updated 2026-11-01
See it in 3D: Ascending aorta · Pulmonary trunk · Pulmonary arteries · Interventricular septum · Right ventricle · Left ventricle
What it is
In persistent truncus arteriosus the truncal and conal ridges fail to fuse, and no aorticopulmonary septum forms. A single vessel with a single valve arises over a VSD and delivers mixed blood to the systemic, coronary and pulmonary circulations. It is cyanotic and strongly linked to 22q11.2 deletion.
Embryological cause
- Weeks 5–7: the truncal and conal ridges fail to form or fuse.
- With no septum the truncus does not divide and a single vessel remains.
- The absent conal septum cannot close the interventricular foramen: an outlet VSD.
- Explained by poor migration of cardiac neural crest through arches 3, 4 and 6.
Markers
- TBX1 (22q11.2)
- Cardiac neural crest
- PAX3
How it presents
- Mild to moderate cyanosis in the first days.
- Fast breathing, sweating and poor weight gain from heart failure as pulmonary resistance falls.
- Bounding pulses; a systolic and sometimes diastolic murmur from truncal valve regurgitation.
- Look for hypocalcemia, infections and the facial features of 22q11.2 deletion.
Diagnosis
- Prenatal or postnatal echocardiography: a single vessel overriding a VSD.
- Pulse oximetry screening; genetic testing for 22q11.2.
- Serum calcium and T-cell count when DiGeorge is suspected.
Test yourself
Think of the answer, then tap the question to see it.
What is the embryological cause of persistent truncus arteriosus?
Failure of the truncal and conal ridges to form or fuse: no aorticopulmonary septum forms.
Which defect always accompanies persistent truncus arteriosus?
A ventricular septal defect, because the missing conal septum cannot close the interventricular foramen.
Which genetic syndrome is associated with truncus arteriosus?
22q11.2 deletion (DiGeorge) syndrome.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
- Ascending aorta
- Pulmonary trunk
- Pulmonary arteries
- Interventricular septum
- Right ventricle
- Left ventricle
Related
- Outflow tract: the spiral aorticopulmonary septum and neural crest
- Transposition of the great arteries
- Tetralogy of Fallot
- 22q11.2 deletion (DiGeorge): the third and fourth pouches
- Neural crest cells and their derivatives
- Ventricular septal defect
Related conditions
Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.
Sources: Langman's Medical Embryology, 13th ed., ch. 13: Cardiovascular System (Wolters Kluwer, 2015); Truncus Arteriosus | Congenital Heart Defects (CHDs) | CDC (Centers for Disease Control and Prevention, 2024).
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Representative model, for educational purposes only.