What Is a Truncus Arteriosus (TA) Anomaly?

Truncus arteriosus (TA) is a rare congenital anomaly characterized by a common arterial trunk from which the ascending aorta and the pulmonary arteries originate distal to the coronary arteries but proximal to the first brachiocephalic branch of the aortic arch (Figure 67.1).

Figure 67.1 Illustration of truncus arteriosus (TA). RA and LA, right and left atrium; RV and LV, right and left ventricles; SVC and IVC, superior and inferior vena cava respectively; TV, MV, tricuspid, mitral, valves respectively; MPA, main pulmonary artery; Ao, aorta.

Image courtesy of Centers for Disease Control and Prevention, USA

The common arterial trunk arises from normal ventricles and the semilunar valve is labeled as a truncal valve. In patients with a normal aortic arch, the ductus arteriosus may be either absent or diminutive.

How Is TA Classified?

The pulmonary artery arises from the TA in many different patterns and is the basis used to classify subtypes of TA. There are two classifications commonly used: Collett and Edwards (1949) and Von Praagh (1965).

The earliest classification, developed by Collett and Edwards, includes TA types I–IV, as follows:

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  Type I TA is characterized by origin of a single pulmonary trunk from the left lateral aspect of the common arterial trunk, with the left and right pulmonary branches arising from the pulmonary trunk.

  
  
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  Type II TA is characterized by separate but proximate origins of the left and right pulmonary arterial branches from the posterolateral aspect of the common arterial trunk.

  
  
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  Type III TA occurs when the branch pulmonary arteries originate independently from the common arterial trunk or aortic arch, most often from the left and right lateral aspects of the trunk.

  
  
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  Type IV TA, originally proposed as a form of the lesion with neither pulmonary arterial branch arising from the common trunk, is now recognized to be a form of pulmonary atresia with ventricular septal defect.

The Van Praagh classification includes four primary types of TA variants:

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  Type A1 is identical to the type I of Collett and Edwards.

  
  
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  Type A2 includes Collett and Edwards type II and most cases of type III, namely those with separate origin of the branch pulmonary arteries from the left and right lateral aspects of the common trunk.

  
  
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  Type A3 includes cases with origin of one branch pulmonary artery (usually the right) from the common trunk, with pulmonary blood supply to the other lung provided either by a pulmonary artery arising from the aortic arch (a subtype of Collett and Edwards type III) or by hyphenate arterial collaterals.

  
  
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  Type A4 is defined not by the pattern of origin of branch pulmonary arteries, but rather by the coexistence of an interrupted aortic arch. In the vast majority of cases of type A4, which fall into the type I of Collett and Edwards, the pulmonary arteries arise as a single pulmonary trunk that then branches. In any of these patterns, intrinsic stenosis, hypoplasia, or both may be present in one or both branch pulmonary arteries, which may have an effect on management and outcome.

What Are the Presenting Signs and Symptoms?

Poor feeding, diaphoresis, tachypnea, and cyanosis are common presenting symptoms with TA although many are prenatally diagnosed by echocardiography.

What Is the Embryological Basis for This Anomaly?

The failure of complete or incomplete septation of the embryonic TA leads to this uncommon anomaly. Because the common trunk originates from both the left and right ventricles, and pulmonary arteries arise directly from the common trunk, a ductus arteriosus is not required to support the fetal circulation.