Truncus arteriosus is a cyanotic congenital heart anomaly in which a single trunk supplies both the pulmonary and systemic circulation, instead of a separate aorta and a pulmonary trunk. It is usually classified as a conotruncal anomaly.
It accounts for up to 2% of congenital cardiac anomalies and is almost always associated with a ventricular septal defect (VSD) to allow circulatory flow circuit completion 1.
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Epidemiology
The estimated incidence is 1 in 10,000 births.
Clinical presentation
Patients may present with signs and symptoms of cyanosis or congestive heart failure.
Pathology
There is a lack of normal separation of the embryological truncus arteriosus into a separate aorta and pulmonary trunk. This results in a single arterial vessel that originates from the heart that supplies the systemic, pulmonary, and coronary circulations. It may also result in a common truncal valve which can contain 2 to 4 cusps.
Classifications
Collett and Edwards system
type I: (most common) both aorta and main pulmonary artery arise from a common trunk
type II: pulmonary arteries arise separately from the posterior aspect of trunk, close to each other just above the truncal valve (negligible main pulmonary artery segment)
type III: (least common) pulmonary arteries arise independently from either side of the trunk
type IV: neither pulmonary arterial branch arising from the common trunk (pseudotruncus), considered a form of pulmonary atresia with a VSD
Van Praagh system
type A1: identical to the type I of Collett and Edwards
type A2: separate origins of the branch pulmonary arteries from the common trunk
type A3: origin of one branch pulmonary artery (usually the right) from the common trunk, with other lung supplied either by collaterals or a pulmonary artery arising from the aortic arch
type A4: presence of an associated interrupted aortic arch
Associations
persistence of primitive aortic arches
Radiographic features
Plain radiograph
Chest radiographs often show moderate cardiomegaly with pulmonary plethora (mainly as a result of collateral formation) and widened mediastinum.
However, the main pulmonary artery (arising from common trunk) may be small/unusual in position which may result in a narrow mediastinum. This along with moderate cardiomegaly and pulmonary plethora gives an appearance that is similar to D-loop transposition of great arteries 9.
Right-sided aortic arch may be seen in ~40% (range 35-50%) of cases 2,10.
Antenatal ultrasound/Echocardiography
Allows direct visualization of a single trunk. Outflow tract views are the most useful. Color Doppler may additionally show flow across both ways through an associated VSD.
CT/CTA
Allows direct visualization of abnormal anatomy.
MRI
Allows direct display of anomalous anatomy. SSFP cine sequences can offer an additional functional assessment.
Treatment and prognosis
Due to parallel fetal circulation, truncus arteriosus does not cause any hemodynamic problem in utero. However it is a major problem postnatally and, if left untreated, approximately 80% of infants die within the first year.