Chest Radiography in Pediatric Cardiovascular Disease

Published on 27/02/2015 by admin

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Chapter 65

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 films. 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 are 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. On the other hand, plain film findings may be specific for some extracardiac lesions, such as supracardiac total anomalous pulmonary venous return, aortic arch anomalies, pulmonary stenosis, and coarctation of the aorta.

A systematic approach to evaluation of the chest film 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 a diagnosis of a cardiovascular disease category such as a shunt or a right- or left-sided obstructive lesion, 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 (Box 65-1).

Box 65-1   Differential Diagnosis of Apparent Gross Cardiomegaly

Technique

As in all medical imaging, attention to detail is necessary to optimize the examination and its interpretation. Proper exposure, centering, collimation, patient positioning, and inspiration are necessary (e-Fig. 65-1).

Many films of infants 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, 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, and barium should be used only if a vascular ring or sling is suspected (and when such findings are likely, cross-sectional imaging should be considered for complete evaluation). Chest fluoroscopy is rarely used except to evaluate prosthetic valve function, the diaphragm, or airway dynamics.

Systematic Interpretation

Normal Anatomy and Physiology

One of the challenges in evaluating the chest radiograph 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.

Newborn infants have physiologic pulmonary hypertension, and as a result, large shunt lesions do not appear until the pulmonary vascular resistance falls, which usually occurs 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.

The physiology of small airways in infants and young 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 would happen in the presence of airway inflammation with bronchiolitis (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, hyperinflation is an important sign of early pulmonary edema.

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