eMedicine Specialties > Radiology > Cardiac

Truncus Arteriosus

Author: Maha Mikhail, MD, MS, FACC, Consulting Staff, Connecticut Multispecialty Group
Coauthor(s): Sherif Wassef, MD, MS, FRCS, Consulting Staff, Department of Vascular and Interventional Radiology, Hahnemann University Hospital
Contributor Information and Disclosures

Updated: Jun 19, 2007

Introduction

Background

Truncus arteriosus is a congenital heart disease characterized by a single great artery that leaves the base of the heart, giving rise to the coronary, pulmonary, and systemic arteries. Wilson described the first case in 1798. Humphreys reviewed and summarized the cases published in the literature up to 1932.

Pathophysiology

Truncus arteriosus results from failed septation of the embryonic truncus by the infundibular truncal ridges. Because the single arterial trunk receives the output of both ventricles, a ventricular septal defect is almost always present (Rosenquist, 1976; Rothko, 1980) (see Image 3; Rothko, 1980; Rosenquist, 1976). A ventricular septal defect is usually large and results from the absence or a pronounced deficiency of the infundibular septum (Anderson, 1977). Truncal valve regurgitation and stenosis are seen in 10-15% of patients each. If truncal insufficiency is severe, signs and symptoms of heart failure may appear shortly after birth. In the uncommon situation in which infants have naturally occurring stenosis of the pulmonary arteries, obvious cyanosis may be present at birth and intensify with age (Mair, 1995).

Frequency

International

The incidence of truncus arteriosus is approximately 0.04 case per 1000 live births (de Roos, 2000). This rare but serious malformation accounts for approximately 1-2% of congenital heart diseases seen at necropsy and approximately 0.7% of all congenital heart diseases (Perloff, 1994). Truncus arteriosus is usually an isolated finding, though it is occasionally associated with anomalies, particularly DiGeorge syndrome and deletion of chromosomal band 22q11 (ie, CATCH 22 deletion, which stands for cardiac anomaly, anomalous face, thymus hypoplasia and/or aplasia, cleft palate, and hypocalcemia) (Radford, 1988; Momma, 1999).

Mortality/Morbidity

Infants with truncus arteriosus seldom reach their first birthday (Butto, 1986). Congestive heart failure is the primary cause of death in the first few months of life unless they receive surgically intervention early in life. This observation underscores the value of prompt and accurate diagnosis to decrease mortality and morbidity in these infants. Patients with truncus arteriosus occasionally reach the third, fourth, or fifth decade (Hicken, 1966; Silverman, 1966).

Race

No racial predilection has been reported in patients with truncus arteriosus (Storch, 1992).

Sex

Truncus arteriosus occurs with equal frequency in male individuals and female individuals (Butto, 1986).

Age

Truncus arteriosus is usually recognized in early infancy, often in the first few weeks of life (Marcelletti, 1976).

Anatomy

Truncus arteriosus is characterized by a single great artery that leaves the base of the heart that gives rise to the coronary, pulmonary, and systemic arteries (see Images 1-3).

The truncus has a single semilunar valve (see Image 2). The truncal valve is tricuspid in 69% of patients, quadricuspid in 22%, and bicuspid in 9%. In rare patients, hexacuspid, pentacuspid, or unicuspid (Van Praagh, 1965; Fuglestad, 1988). No second atretic semilunar valve is present, as is usually found in aortic and pulmonary valve atresias (Perloff, 1994). A right aortic arch is associated with truncus arteriosus in 15-30% of patients (Glew, 1991).

Classification systems

In truncus arteriosus, 4 anatomic types are recognized on the basis of the anatomic origin of the pulmonary arteries, according to Collette and Edwards (Collette, 1949).

• Type I: In this common type, a short pulmonary trunk arises from the truncus arteriosus, giving rise to both pulmonary arteries (see Image 4).
• Type II: Each pulmonary artery arises separate from but close to the other from the posterior aspect of the truncus (see Image 4).
• Type III: Each pulmonary artery arises from the lateral aspect of the truncus (see Image 4).
• Type IV: Pseudotruncus is currently considered to represent a form of pulmonary atresia with ventricular septal defect, ie, a severe form of tetralogy of Fallot rather than truncus arteriosus (Sotomora, 1978) (see Image 17).

In 1965, Van Praagh introduced a new classification with 4 subtypes.

• Type 1 is similar to type I Collette and Edwards described (see Image 5, Image 25).
• Type 2 mostly comprises types II and III Collette and Edwards described, in which the proximity of the origin of the pulmonary arteries is not specified (see Image 6).
• In type 3, 1 pulmonary artery branch does not arise from the common pulmonary trunk and originates from the ductus arteriosus or directly from the aorta (see Image 7).
• In type 4, the aortic arch is hypoplastic or interrupted, and a large patent ductus arteriosus is present (see Image 8).

In addition, the Van Praagh classification specifies the presence (subtype A) or absence (subtype B) of ventricular septal defect. Each case is accordingly assigned a nomenclature that includes a letter and a number (Van Praagh, 1965).

Although both classifications have found wide application in clinical cardiology and cardiac surgery, each has limitations. Collette and Edwards type IV is probably a misnomer, because it describes a separate entity with different therapeutic and prognostic implications. In addition, cardiothoracic surgeons often refer to a type 1½, which is similar to type I but with a shallow aorticopulmonary segment. This fairly common entity is not included in either classification (Jacobs, 2000).

The term hemitruncus has fallen out of use, but it refers to a rare anomaly in which 1 pulmonary artery branch, usually the right, arises from the ascending aorta just above the aortic sinuses, while the main pulmonary artery and the other pulmonary artery branch arise in their normal positions.

Cardiac anomalies associated with truncus arteriosus

Several cardiac anomalies are associated with truncus arteriosus.

A right aortic arch with mirror-image brachiocephalic branching occurs in 21-36% of patients with truncus arteriosus (Van Praagh, 1965; Calder, 1976; Butto, 1986) (see Image 10).

Hypoplasia of the aortic arch with or without coarctation occurs in 3% of patients (Crupi, 1977).

An interrupted aortic arch occurs in 11-19% of patients and is accompanied by ductal continuity of the descending thoracic aorta Van Praagh, 1965; Calder, 1976; Crupi, 1977; Butto, 1986).

In approximately one half of patients, the ductus arteriosus is absent, whereas in the other half, the ductus remains patent postnatally (Van Praagh, 1965; Calder, 1976).

In 16% of patients, 1 pulmonary artery is absent on the side of the aortic arch (Mair, 1974) (see Image 11).

Anomalies of the coronary artery are common and include a small leftward-displaced left anterior descending coronary artery, a prominent conus branch of the right coronary artery supplying the right ventricular outflow tract, an origin of the posterior descending artery from the circumflex artery in 27% of patients (a rate 3 times higher than that of the general population), and anomalies of coronary ostial origin in 37-49% of patients (Van Praagh, 1965; Calder, 1976; de la Cruz, 1990; Mair, 1995).

Other associated anomalies include secundum atrial septal defect in 9-20% of patients, an aberrant subclavian artery in 4-10% (see Images 15-16), a persistent left superior vena cava in 4-9%, and mild tricuspid stenosis in 6%.

Rare associated anomalies include a partial anomalous pulmonary venous connection, tricuspid atresia, mitral atresia, ventricular inversion, and an asplenia complex (Mair, 1974; Marino, 1990; Gumbiner, 1991; Rao, 1991; Rice, 1991).

Extracardiac anomalies observed in 21-30% of autopsy cases include skeletal deformities, hydroureter, bowel malrotation, and multiple complex anomalies (Mair, 1995).

Presentation

Infants appear physically underdeveloped and cyanotic. During the first weeks of life in healthy infants and in infants with truncus arteriosus, pulmonary arteriolar resistance is usually increased. Mild cyanosis is noted owing to the high pulmonary vascular resistance with little evidence of cardiac decompensation. As pulmonary resistance decreases, flow through the lungs gradually increases, and cyanosis may disappear. However, tachycardia, tachypnea, excessive sweating, poor feeding, and other signs of heart failure may begin to appear because of excessive pulmonary blood flow (Mair, 1995).

The heart is often overactive. A left precordial bulge may be noted, and a systolic thrill is often palpable along the left sternal border. The first heart sound is normal and frequently followed by a loud ejection click coinciding with maximal opening of the truncal valve (Ritter, 1975). The second heart sound is usually loud and single. An apical third heart sound often is present. A loud pansystolic murmur is often heard at the lower left sternal border and radiating to the entire precordium. A blowing, diastolic high-pitched murmur is usually best heard along the left sternal border. Obvious cyanosis is present, and clubbing of the fingers may be seen.

Preferred Examination

Chest radiography usually is the initial investigation performed in the neonatal period. Cardiomegaly is frequently present at birth. Chest radiographic findings usually reveal the increase in pulmonary arterial blood flow manifesting as increased pulmonary vascular markings (see Image 9). The combination of a right-sided aortic arch, cardiomegaly, and increased pulmonary vascularity strongly suggests truncus arteriosus; however, further diagnostic investigations are always needed to confirm the diagnosis (Strife, 1998).

Echocardiography has markedly changed the evaluation, diagnosis, and management of congenital heart disease. Echocardiographic findings, usually diagnostic, demonstrate the origin and configuration of the pulmonary arteries, the ventricular septal defect, the truncus arteriosus, and the aortic arch, as well as the status of the truncal valve. Complete echocardiographic examination can be performed to establish goal-directed treatment, to almost eliminate the need for confirmatory cardiac catheterization, and to provide a cost-effective feasible tool for close follow-up observation of patients after surgery.

CT is another imaging modality that can be used to evaluate infants with complex congenital heart disease. Standard CT scans are useful for evaluating suggested anomalies of the aortic arch, a double aortic arch, and retroesophageal vascular structures indicating an anomalous origin of the subclavian artery. Electron-beam CT (EBCT) accurately defines systemic and pulmonary venous connections, demonstrating other anomalies associated with truncus arteriosus, including abnormalities of the pulmonary artery.

Contrast-enhanced EBCT and MRI are the noninvasive procedures of choice for the diagnosis and exclusion of anomalies of the origin and course of the coronary arteries. Standard CT, EBCT, and MRI are useful, noninvasive techniques for visualizing the cardiovascular anatomy in patients with congenital heart disease. EBCT and MRI can also enable assessment of cardiovascular function. MRI appears to be the most suitable of these techniques for assessing congenital heart disease (Higgins, 1984).

By comparing angiographic and 2-dimensional (2D) echocardiograms, MRI enables accurate anatomic diagnosis of complex congenital heart diseases. In some instances, MRI can replace the need for invasive cardiac catheterization or reduce the number of catheterizations required in the care of patients with complex congenital heart disease. MRI of complex congenital heart diseases is necessary for preoperative assessment in adults and in infants, and the results influence surgical planning by providing information about the anatomic topography of the vascular malformation and its relation to the bronchial system. MRI is reliable in classifying truncus arteriosus by showing the anatomy of the pulmonary artery. The size of the pulmonary artery and its branches can be measured in the transverse, coronal, and sagittal planes (Frank, 2003).

Cardiac catheterization is usually performed to confirm anatomic details and to obtain physiologic data regarding pulmonary vasculature and to accurately calculate pulmonary vascular resistance (Strife, 1998). Cardiac catheterization is important in helping make decisions regarding the time and type of surgery (palliative vs corrective)

The role of nuclear imaging in the diagnosis of truncus arteriosus is not well established. However, all the other modalities, including cardiac angiography, are the standard of care for diagnosing this complex congenital cardiac disease with all its associated anomalies. Of note, echocardiography is the modality of choice for diagnosing truncus arteriosus, and the other investigations are complementary.

Limitations of Techniques

Although imaging modalities have improved tremendously in recent times, some limitations remain. One fairly common pitfall with imaging techniques is the suggestion of the presence of a partially formed aorticopulmonary septum and, therefore, the presence of a main pulmonary segment. However, at surgery, the branch pulmonary artery orifices may be found adjacent to one another in the left posterolateral aspect of the common arterial trunk. The surgeon may be unable to excise a main pulmonary artery segment from the common arterial trunk, even when the segment was depicted on images because it may have no actual length (Jacobs, 2000).

Differential Diagnoses

Asplenia/Polysplenia
Ebstein Anomaly
Pulmonic Stenosis
Tetralogy of Fallot
Tricuspid Atresia

Other Problems to Be Considered

Aortic atresia
Aorticopulmonary window
Common atrium
Double-outlet right ventricle
Single ventricle
Pulmonary atresia
Pulmonary stenosis with atrial septal defect
Tricuspid atresia with pulmonary stenosis
Transposition of the great vessels with pulmonary stenosis
Total anomalous venous return above the diaphragm

• Search for CME/CE on This Topic »

• Truncus Arteriosus (Pediatrics: Cardiac Disease and Critical Care Medicine)
• Interrupted Aortic Arch (Pediatrics: Cardiac Disease and Critical Care Medicine)
• Aortopulmonary Window, Surgical Treatment (Pediatrics: Cardiac Disease and Critical Care Medicine)
• Eisenmenger Syndrome (Cardiology)

• Prevalence of Severe Congenital Heart Disease After Folic Acid Fortification of Grain Products: Time Trend Analysis in Quebec, Canada
• What is the Most Likely Diagnosis for a Cyanotic Newborn?