Teaching Case

A 5-year-old boy's history revealed that he had been diagnosed with congenital cardiac malformation at the age of 3 years. He was weaker than normal children and showed oral cyanosis, and grade 3/6 ejection systolic murmur heard best at apex and left sternal border. He had no clubbed fingers, history of injury, previous surgery or any relevant family history.

A chest X-ray revealed increased vascular markings and no widened mediastinum, and heart shadow size and shape was within the normal range. (Fig. 1)
Dual-source computed tomography (DSCT) angiography showed the right ventricle and atrium markedly enlarged, ventricular septa defect, atrial septa defect, the dilated trunk artery overriding both ventricles (maximal transverse diameter: 25 mm), absence of the main pulmonary arterial trunk, and adjacent left and right pulmonary arteries (PAs) arising from the dorsal aspect of the descending aorta. At the same time, we can see the persistent left superior vena cava in the picture. (Fig. 2-4).

Background: Persistent truncus arteriosus (PTA) is a rare conotruncal defect, accounting for under 1% of all congenital heart diseases. [1] It is usually defined as a single arterial vessel arising from the heart, which supplies systemic, coronary and pulmonary blood flow. Over 80% of patients succumb to heart failure in infancy. [2] Collet and Edward classified PTA as 4 major types based on an embryonic theory. Type I is the most common, both pulmonary arteries arise from the single branch and the single branch arises from the truncus; Type II, the main pulmonary arterial trunk is absent, and right and left pulmonary arteries (PAs) arise from the posterior aspect of the truncus separately but adjacent to each other; Type III, the two pulmonary arteries arise from each side of the truncus; Type IV, there is no true branch of a pulmonary artery arising from the truncus and they originate from the descending aorta. The literature suggests that the type IV PTA with persistent left superior vena cava is rare.
Clinical perspective: PTA can lead to lower-than-normal oxygen levels in the arterial blood, and patients with PTA who do not undergo surgical intervention have a high mortality rate due to heart failure [2], so early diagnosis is crucial. The cardiac malformations in the patients are often accompanied by the micro-deletion of chromosome 22 q11. 2, including PTA. Therefore early recognition of the deletion is important [3]. Imaging techniques can provide a diagnosis and guide the therapeutic management.
Imaging perspective: Computed tomography angiography is able to help diagnose a PTA and locate the origin of the pulmonary arteries.
DSCT 3D imaging (Maximum Intensity Projection, Multiple Planar Reconstruction and Volume Rendering) can be intuitive and accurately display the distribution and the origin of vessels. It can not only determine the classification of the disease but also determine the scope of the surgical procedure.
Outcome: Type IV PTA with persistent left superior vena cava.
Take Home Message, Teaching Points:
- If a PTA is diagnosed with Doppler echocardiography and computed tomography angiography, it is beneficial for the pathological classification and the diagnosis of coexisting deformities.
- PTA is common in infants and young children and its early mortality is high, if not treated, patients rarely reach middle age.
- PTA is curable and the definitive treatment of PTA is surgery.