46 Truncus Arteriosus with DiGeorge Syndrome

Clinical Presentation

A newborn presents with mild cyanosis and failure to thrive.

Figure 46A

Radiologic Findings

The frontal chest radiograph (Fig. 46A1) shows a moderately enlarged heart with an egg-on-side configuration and increased pulmonary vascularity. The superior mediastinum is narrow because of thymic hypoplasia. Note that the anterior upper mediastinum is empty in lateral view (Fig. 46A2).

Figure 46B Schematic diagram of four types of truncus arteriosus as described by Collet and Edwards.

Diagnosis

Truncus arteriosus with DiGeorge syndrome

Differential Diagnosis

Egg-on-side appearance:
- Complete transposition of the great arteries: pulmonary vascularity, variable
- Pulmonary atresia with intact ventricular septum: diminished pulmonary vascularity
- Truncus arteriosus: increased pulmonary vascularity
Boot-shaped heart: In truncus arteriosis the heart may also be boot shaped, but this is less common.
- Tetralogy of Fallot: normal heart size and diminished pulmonary vascularity
- Pulmonary atresia with ventricular septal defect: normal heart size with diminished pulmonary vascularity or enlarged heart with increased pulmonary vascularity
- Truncus arteriosus: moderate cardiomegaly with increased pulmonary vascularity
Narrow superior mediastinum:
- Complete transposition of the great arteries with postnatal regression of the thymus
- Truncus arteriosus with thymic hypoplasia in association with DiGeorge syndrome or postnatal regression of the thymus

Discussion

Clinical Findings

Most patients with truncus are recognized as having congenital heart disease during the neonatal period. During the first few weeks of life, persistence of increased pulmonary vascular resistance results in mild cyanosis with little evidence of heart failure. As the pulmonary vascular resistance decreases, cyanosis may disappear and be replaced by signs of congestive heart failure. When the truncal valve is severely regurgitant, the signs of congestive heart failure may manifest immediately after birth. Generally, the heart is overactive, and a pansystolic murmur is heard at the left precordium. Microdeletion of chromosome 22q11 is seen in ~40% of patients with truncus, and patients with this deletion include DiGeorge and velocardiofacial syndrome cases.