Chest Radiography in Pediatric Cardiovascular Disease

The role of chest radiography in the diagnosis and evaluation of congenital cardiovascular disease continues to evolve. At one time a major tool in the assessment of heart disease, radiography now occupies an ancillary role, with echocardiography serving as the major primary investigation after physical examination, especially in the neonatal period. However, the chest radiograph still may provide the first indication of unsuspected cardiovascular disease, and in infants and children with known cardiac disease radiography offers an important overview of the heart and pulmonary circulation. Moreover, chest radiography is a vital tool in the early postoperative period and is useful in the follow-up of heart disease. These latter topics are beyond the scope of this chapter.

The major chest radiographic findings in patients with cardiac disease are cardiomegaly, pulmonary vascular changes (predominantly overcirculation or undercirculation), and signs of pulmonary venous hypertension and edema. However, several caveats need to be emphasized. First, children with relatively mild structural defects and even some children with severe or complex disease may have normal chest radiographs. This situation is particularly true in newborns. In addition, the chest radiograph usually does not provide useful information about specific chamber size, hypertrophy, or intracardiac connections or malformations. Echocardiography, magnetic resonance imaging, computed tomography, or angiography is needed for precise evaluation of intracardiac structure and function. Furthermore, findings such as a boot-shaped or egg-shaped heart are nonspecific for tetralogy of Fallot or transposition of the great arteries, respectively. On the other hand, plain radiographic findings may be specific for some extracardiac lesions, such as supracardiac total anomalous pulmonary venous return, pulmonary stenosis, aortic arch anomalies, and coarctation of the aorta.

A systematic approach to evaluation of the chest radiograph consists of an assessment of heart size, shape, and position; pulmonary vasculature; the airway and mediastinum; visceral situs; and skeletal abnormalities. Applying such an approach often results in the recognition of a cardiovascular disease category, which in turn leads to a differential diagnosis and the identification of the likely etiology of nonspecific clinical findings, such as congestive heart failure or cyanosis.

Technique

Proper exposure, centering, collimation, patient positioning, and inspiration are necessary to optimize the examination and its interpretation ( e-Fig. 65.1 ). Many infant radiographs are obtained using the anteroposterior projection and supine position. Because of the small size of the chest, this technique results in little magnification of the heart, as can be seen in larger children. Beam angulation also may affect the appearance of the heart and great vessels. With lordotic positioning or low centering for a combined chest and abdomen radiograph, the heart may appear more globular, with an uplifted apex and accentuation of the pulmonary outflow tract; with reverse lordosis, much of the heart may be obscured by the hemidiaphragms. Oblique views are not useful for cardiac evaluation. Chest fluoroscopy is rarely used except to evaluate prosthetic valve function, the diaphragm, or airway dynamics.

e-Figure 65.1, Normal chest examination in an infant.

Systematic Interpretation

Normal Anatomy and Physiology

One of the challenges in evaluating the chest radiographs of younger children is their variable anatomy and physiology. For example, the thymus is variable in size and position and may mimic cardiomegaly, abnormally positioned vessels, pericardial fluid, or a mediastinal mass ( e-Fig. 65.2 ). It is rare for the thymus to extend posteriorly. The thymus usually causes few problems in the interpretation of chest radiographs in children older than 6 years.

e-Figure 65.2, Normal chest examination in an infant.

Newborn infants have physiologic pulmonary hypertension, and as a result, large shunt lesions do not become apparent until the pulmonary vascular resistance falls, which usually manifests by 4 to 6 weeks ( Fig. 65.3 ). Similarly, newborn infants may not show the expected changes of severe pulmonary stenosis or atresia if the ductus arteriosus is patent.

Figure 65.3, Complete transposition of the great arteries in a neonate.

The physiology of small airways in infants and children up to approximately 2 years of age results in unique manifestations of pulmonary edema. Specifically, infants show hyperinflation as a response to interstitial edema, as happens in airway inflammation with bronchiolitis (see Figs. 65.3 and 65.4 ). The hyperinflation occurs as an adaptive response to the interstitial edema to prevent small airway closure. In the absence of clinical signs of a respiratory infection or aspiration, hyperinflation is an important sign of early pulmonary edema.

Figure 65.4, Total anomalous pulmonary venous return with obstruction in an infant.

Heart Size

The size of the heart can be difficult to assess in the frontal projection of infants and young children because of the presence of the relatively large thymus and poor inspiration (see e-Figs. 65.1 and 65.2 ). Measurement of the cardiothoracic ratio is of little use. The lateral view provides a more reliable indication of true heart size by permitting an assessment of the anteroposterior dimension without interference from the thymus. However, the thymus does fill in the retrosternal space, obscuring the right ventricular outflow tract. Posterior displacement of the trachea can be indicative of cardiac enlargement. In older children, the frontal radiograph is more useful; however, the radiologist should evaluate both views to assess the three-dimensional volume of the heart. In a child with pectus excavatum, the heart may appear large in the frontal view but compressed on the lateral view. Marked cardiomegaly is seen in children with severe valve regurgitation, especially tricuspid valve disease (Ebstein anomaly), pericardial effusion, and cardiomyopathy, and it is rarely seen in children with cardiac tumors. Mediastinal masses may mimic cardiomegaly ( Box 65.1 , e-Fig. 65.5 ).

Box 65.1

Differential Diagnosis of Severe Cardiomegaly

Volume loading, as seen with severe valve regurgitation (e.g., Ebstein anomaly or pulmonary atresia with intact ventricular septum), large shunts, or both
Pump failure, as seen with cardiomyopathy (including anomalous origin of the left coronary artery from the pulmonary artery)
Pericardial disease
Cardiac or mediastinal mass

e-Figure 65.5, Ebstein anomaly in an infant.

Pulmonary Vasculature

Chest radiography provides a window into the pulmonary circulation, which is the main area in which chest radiography supplements the information gained from echocardiography. The pulmonary vasculature may show evidence of increased flow, decreased flow, normal flow, or pulmonary venous hypertension. The assessment of the pulmonary vasculature is both important and difficult. Poor-quality images that are rotated or obtained during expiration are difficult to interpret (see e-Fig. 65.1 ). Many radiographs in younger children are obtained in the supine position, and therefore flow is symmetric from base to apex.

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