Applied Radiology

Although a definitive diagnosis of most types of congenital heart disease is made with echocardiography, chest radiographs often are the initial imaging study used. Accurate interpretation of these radiographs facilitates appropriate work-up and management.

Cardiomegaly in the newborn may be associated with many types of congenital heart disease or systemic illness. However, when a massive "wall-to-wall" cardiothymic silhouette is found on a chest radiograph, the possible causes are fewer. Most cases of wall-to-wall heart are related to massive right atrial enlargement, found in such disorders as Ebstein's anomaly of the tricuspid valve or pulmonary atresia with intact ventricular septum (PA-IVS).1-3 Other causes of a massive cardiac silhouette include pericardial effusions, atypical large arteriovenous shunts, hypertrophic cardiomyopathy in infants of diabetic mothers, and cardiac or mediastinal masses mimicking massive cardiomegaly.

There may be some degree of overlap in the clinical presentation of this group of neonates. Newborns with noncardiac causes of massive cardiac silhouette can present with symptoms similar to those with congenital heart disease, which are tachypnea and wheezing. Cyanosis also may be present, related to cardiac or venous compromise secondary to compression.

Massive right atrial enlargement PA-IVS and Ebstein's anomaly can result in massive right atrial enlargement. This produces the largest cardiac silhouettes seen in neonates.1-3 When massive cardiomegaly is associated with decreased pulmonary flow, Ebstein's anomaly or PA-IVS is the most likely diagnosis. The degree of cardiomegaly in PA-IVS is related to the competency of the tricuspid valve.1

When tricuspid regurgitation is present, blood flows "back and forth" from the right ventricle to the right atrium, and the right atrium and right ventricle can become massively enlarged (figure 1).1 In Ebstein's anomaly, there is redundancy and downward displacement of the leaflets of the tricuspid valve into the right ventricle, with adherence of these leaflets to the right ventricular wall distal to the atrioventricular annulus. This results in a tripartite right heart, divided into the right atrium, an atrialized right ventricle

(portion of the right ventricle located between the atrioventricular annulus and the displaced tricuspid valve), and the right ventricle.4 A combination of functional and structural obstruction leads to massive enlargement of the anatomic right atrium and atrialized right ventricle (figure 2).3,4

Hypertrophic cardiomyopathy in infants of diabetic mothers

In infants of diabetic mothers, an increase in myocardial mass may result in hypertrophic cardiomyopathy and can be a cause of massive cardiomegaly (figure 3).5,6 Congestive heart failure also can contribute to the degree of cardiomegaly.5 In these neonates, there is enlargement of the myocardial cell resulting in increased myocardial mass. This myocardial hypertrophy can result in diminished left ventricular function (nonobstructive cardiomyopathy), as well as left ventricular outflow tract obstruction (obstructive cardiomyopathy).5

Another cause of cardiomyopathy in neonates is hypoxic-ischemic cardiomyopathy, or the so-called "stunned myocardium." Hypoxia related to birth asphyxia can result in temporary myocardial dysfunction and resultant cardiac enlargement.

Large arteriovenous shunts

When very large amounts of arteriovenous shunting occurs, resultant cardiomegaly can be massive. These atypically large shunts can be peripheral, such as arteriovenous malformations of the liver, brain, or skin (figure 4), or intracardiac, such as a coronary artery-right heart fistula (figure 5).7 In these cases, pulmonary vascularity may be normal on radiographs because the increased pulmonary vascular resistance present in newborns impedes any increase in pulmonary arterial flow.

Large pericardial effusions

Pericardial effusion in the absence of hydrops fetalis or sepsis is rare in neonates.8 In a previous review of 32 cases of neonatal pericardial effusion, cardiac tumor was a common cause (38%), with teratoma and cavernous hemangioma/hemangioma being the most common types.8 Other common causes included thyroid dysfunction (21%), infection (12%), and diaphragmatic hernia into the pericardial sac (16%).8 When large enough, pericardial effusions can cause massive enlargement of the cardiac silhouette (figure 6).

Masses mimicking cardiac chamber enlargement

Chest masses can sometimes produce the radiographic "wall-to-wall" appearance of the heart in newborns, mimicking diseases such as Ebstein's anomaly. We have seen this occur with cardiac masses such as rhabdomyomas (figure 7), mediastinal masses such as teratomas (figure 8), and congenital diaphragmatic hernias on early films, before gas enters the bowel (figure 9). Children with tuberous sclerosis are predisposed to developing rhabdomyomas.

Technical factors

Many technical factors can influence the apparent cardiac size seen on frontal radiographs. In neonatal intensive care units, radiographs often are obtained using the portable anterior-posterior technique in frontal projection only. Anterior-posterior projection, lordotic or rotated positioning, and large focus-film distance all may cause the magnification of apparent cardiac size.9 Under these circumstances, a normal heart can appear to be enlarged (figure 10), especially if the film is obtained during expiration. Additionally, a normal thymus can appear large relative to the newborn mediastinum and mimic cardiomegaly on frontal radiographs. In cases where cardiac enlargement is in question on frontal radiographs, lateral radiographs are helpful in determining whether cardiac enlargement is true or artifactual. AR

References

1. Kanjuh VI, Stevenson JE, Amplatz K, et al: Congenitally unguarded tricuspid orifice with coexistent pulmonary atresia. Circulation 30:911-915, 1964.

2. Anderson KR, Lie JT: Pathologic anatomy of Ebstein's anomaly of the heart revisited. Am J Cardiol 41:739-745, 1978.

3. Strife JL, Bisset GS III: Cardiovascular system. In: Kirks DR (ed), Practical Pediatric Imaging, pp 417-513. Boston, Little, Brown and Company, 1991.

4. Bialostozky D, Horwitz S, Espino-Vela J: Ebstein's malformation of the tricuspid valve: A review of 65 cases. Am J Cardiol 29:826-836, 1972.

5. Dunn V, Nixon GW, Jaffe RB, Condon VR: Infants of diabetic mothers: Radiographic manifestations. AJR 137:123-128, 1981.

6. Way GL, Wolfe RR, Eshaghpour E, et al: The natural history of hypertrophic cardiomyopathy in infants of diabetic mothers. J Pediatrics 95:1020-1025, 1979.

7. Jaffe RB, Glancy DL, Epstein SE, et al: Coronary arterial-right heart fistulae: Long-term observations in seven patients. Circulation 47:133-143, 1973.

8. Cartagena AM, Levin TL, Issenberg H, Goldman HS: Pericardial effusion and cardiac hemangioma in the neonate. Pediatr Radiol 23:384-385, 1993.

9. Amplatz K, Moller JH: Radiology of Congenital Heart Disease, pp 55-113. St. Louis, Mosby-Year Book, Inc., 1993.