Florianopolis, Brazil

Definition

Truncus arteriosus is an anomaly characterized by a single arterial vessel attached to both ventricles and overriding the ventricular septum[1].  The truncus is a large vessel with a generally dysplastic atrioventricular valve with three, two or one leaflets. A ventricular septal defect is associated with truncus arteriosus in most instances.  In 40% of the cases, the arterial trunk connects predominantly with the right ventricle, in 40% of the cases the overriding is symmetrically distributed over both ventricles and in 20% of the cases the arterial trunk connects mainly with the left ventricle.

Depending on where and how the pulmonary artery is connected to the trunk, truncus arteriosus can be classified in types 1, 2, 3 and 4[3]:

1. [4] classified the disorder in types A and B. In type B, there is no associated ventricular septal defect.  Type is divided in:
   1. [5].

      Prevalence

      0.3:10,000 births. Incidence may be 12 times higher in women with pregestational diabetes mellitus[6].

      Etiology

      Failure of the truncus arteriosus to divide during in the embryonic period.

      Diagnosis

      Ultrasound diagnosis is made by the observation of a common arterial trunk overriding the ventricular septum.  In types 1 or 3, (Figure 1), a pulmonary trunk is observed arising directly from the truncus arteriosus.  In types 2 and 4, it may be difficult to image the pulmonary artery and thus, differentiation from pulmonary stenosis associated with a ventricular septal defect or tetralogy of Fallot may only be possible after birth.

Figure 1. Oblique section through the superior portion of the ventricular septum, showing the truncus arteriosus and a pulmonary branch arising from the left aspect of the vessel.

Figure 2. Color Doppler of the truncus arteriosus showing high velocity blood  and turbulent blood flow.

Figure 3.  Four chamber view of the fetal heart with color Doppler demonstration of the large ventricular septal defect.

Figure 4.  Four chamber view of the fetal heart.  Note that this image appears normal, thus highlighting the importance of imaging the outflow tracts in every case.

Differential diagnosis

Pulmonary atresia associated with either a ventricular septal defect or tetralogy of Fallot for the reasons exposed above.

Prognosis

Hemodynamics is not affected during intrauterine life.  Cardiac failure occurs after birth because of the fall in blood pressure in the pulmonary circulation and it is frequently a medical emergency.

Prenatal management

When truncus arteriosus is suspected, a detailed fetal echocardiogram is mandatory as well as evaluation of all other organs to rule out associated anomalies.  Although a somewhat rare anomaly, it has been estimated that chromosomal anomalies occur in approximately 10% of the fetuses with truncus arteriosus.  It should also be remembered that DiGeorge, velocardiofacial (DFG/VCFS) and conotruncal anomaly face syndromes (CTAFS) are associated with conotruncal anomalies.  These three syndromes are caused by a microdeletion in chromosome 22q11.2 and are collectively known as "CATCH22".  They are associated with extracardiac malformations that are difficult to detect prenatally and even during the first few years of life. The microdeletion in chromosome 22q11.2 may be diagnosed by FISH (fluorescence in situ hybridization)[7].  Therefore, we think that karyotyping should be offered as well as detection of the 22q11 microdeletion by FISH in cases of truncus arteriosus detected prenatally.

Treatment

Treatment consists in closing the ventricular septal defect and creating a connection between the right ventricle and the pulmonary circulation. Survival rate to surgical intervention is approximately 90%2.

Recurrence risk

For siblings (1% empirical)[8] (Victorica, 1990)

References