Truncus arteriosus vs Tetralogy of Fallot and transposition
How to tell Truncus arteriosus and Tetralogy of Fallot and transposition apart when a board question makes them look alike.
Truncus is one trunk; TOF is obstructed RV outflow with VSD; TGA is parallel switched arteries.
Side by side
Single arterial trunk overriding a VSD supplies systemic, pulmonary, and coronary circulations.
TOF has two great arteries with RV outflow obstruction; TGA has switched great arteries creating parallel circuits requiring mixing.
Failure of aorticopulmonary septation leaves one common outflow tract.
TOF reflects anterior malalignment of outflow septum; TGA reflects failure of normal spiral septation.
One semilunar/truncal valve and one arterial trunk points truncus.
Tet spells/squatting point TOF; severe neonatal cyanosis improved by mixing lesions points TGA.
The trap
All are conotruncal cyanotic defects, so count the great arteries and ask whether circuits are mixed or parallel.
Watch it explained
The repair move
For conotruncal cyanotic congenital defects, draw the outflow tracts before naming the lesion: (1) truncus arteriosus = a single great vessel overrides a VSD (failure of aorticopulmonary septation), with cyanosis from mixing; (2) tetralogy of Fallot = pulmonary outflow obstruction plus overriding aorta plus VSD plus RVH (boot-shaped heart, tet spells relieved by squatting); (3) transposition of the great arteries = aorta off the RV and pulmonary artery off the LV in parallel circulations (severe neonatal cyanosis, survival depends on mixing through ASD/VSD/PDA, give prostaglandin E1 to keep ductus open until atrial septostomy or arterial switch).
Try a free question
CoreA newborn has cyanosis and heart failure. Imaging shows one arterial trunk overriding a VSD and supplying systemic, pulmonary, and coronary circulations. Which conotruncal defect is most likely?
Show answer and explanation
Answer: A. Truncus arteriosus. Truncus arteriosus has a single arterial trunk arising from the ventricles with VSD and mixed blood.
Why the other choices are tempting
- B. TOF has pulmonary stenosis, VSD, overriding aorta, and RVH but two great arteries.
- C. TGA has aorta from RV and pulmonary artery from LV, creating parallel circuits.
- D. TAPVR involves pulmonary veins draining abnormally to systemic venous circulation.
- E. Coarctation is narrowing of the aorta.
Flashcards
Tap a card to flip it.
What is the fastest separator for Truncus arteriosus vs Tetralogy of Fallot and transposition?
Truncus is one trunk; TOF is obstructed RV outflow with VSD; TGA is parallel switched arteries.
What clue should make you choose Truncus arteriosus?
Single arterial trunk overriding a VSD supplies systemic, pulmonary, and coronary circulations.
Quick answers
What is the fastest way to tell Truncus arteriosus from Tetralogy of Fallot and transposition?
Truncus is one trunk; TOF is obstructed RV outflow with VSD; TGA is parallel switched arteries.
What is the key clue for Truncus arteriosus?
Single arterial trunk overriding a VSD supplies systemic, pulmonary, and coronary circulations.
What is the key clue for Tetralogy of Fallot and transposition?
TOF has two great arteries with RV outflow obstruction; TGA has switched great arteries creating parallel circuits requiring mixing.
What is the common trap with Truncus arteriosus vs Tetralogy of Fallot and transposition?
All are conotruncal cyanotic defects, so count the great arteries and ask whether circuits are mixed or parallel.