DOI: 10.1148/rg.275065148
RadioGraphics 2007;27:1323-1334
© RSNA, 2007
Classic Imaging Signs of Congenital Cardiovascular Abnormalities1
Emma C. Ferguson, MD,
Rajesh Krishnamurthy, MD, and
Sandra A. A. Oldham, MD, FACR
1 From the Department of Diagnostic and Interventional Imaging, Section of Thoracic Imaging, University of Texas Medical School at Houston, 6431 Fannin St, Suite 2.026, Houston, TX 77030 (E.C.F., S.A.A.O.); and the Department of Diagnostic Imaging, Texas Children’s Hospital, Houston, Tex (R.K.). Presented as an education exhibit at the 2005 RSNA Annual Meeting. Received August 7, 2006; revision requested September 25 and received October 31; accepted November 3. All authors have no financial relationships to disclose.
Address correspondence to E.C.F. (e-mail: ecferguson{at}hotmail.com).
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Abstract
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Cardiovascular imaging is a rapidly evolving field that requires familiarity with the appearances of pediatric and adult cardiovascular diseases on chest radiographs as well as images obtained with computed tomography, magnetic resonance imaging, and angiography. To accurately identify congenital abnormalities affecting the heart and vessels of the thorax, radiologists must recognize the imaging features and understand their pathophysiologic origin. The cardiovascular imaging signs of congenital anomalies that are most often seen in radiologic practice include the egg on a string (seen in transposition of the great arteries), snowman (total anomalous pulmonary venous return), scimitar (partial anomalous pulmonary venous return), gooseneck (endocardial cushion defect), figure of three and reverse figure of three (aortic coarctation), boot-shaped heart (tetralogy of Fallot), and box-shaped heart (Ebstein anomaly).
© RSNA, 2007
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LEARNING OBJECTIVES
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After reading this article and taking the test, the reader will be able to:- Recognize the classic signs of congenital cardiovascular abnormalities.
- Describe the anatomic and pathologic features represented by each sign and discuss their clinical importance.
- Identify the modality that best depicts each sign.
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Introduction
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A number of imaging signs of congenital cardiovascular abnormalities have been widely described in the radiology literature and are generally recognized to be clinically important. Many were named for familiar objects that the imaging features vaguely resemble. Radiologists must be able to recognize these signs and must understand their causes in order to provide accurate diagnoses of abnormalities affecting the heart and vessels of the thorax.
The article provides an overview of classic signs of congenital cardiovascular abnormalities. These signs include the egg on a string (which represents transposition of the great arteries), snowman (total anomalous pulmonary venous return [TAPVR]), scimitar (partial anomalous pulmonary venous return), gooseneck (endocardial cushion defect), boot-shaped heart (tetralogy of Fallot), figure of three and reverse figure of three (aortic coarctation), and box-shaped heart (Ebstein anomaly). The pathophysiologic origin of each sign is explained, and the characteristic imaging features are described in detail.
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Transposition of the Great Arteries and Egg-on-a-String Sign
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Transposition of the great arteries, the most common cyanotic congenital heart lesion found in neonates, accounts for 5%–7% of congenital cardiac malformations. It is most common in infants of diabetic mothers. It is isolated in 90% of those affected and rarely is associated with a syndrome or an extracardiac malformation.
In the normal anatomy, the aorta is anterior to and at the right of the pulmonary artery; in transposition of the great arteries, the pulmonary artery is situated to the right of its normal location and is obscured by the aorta on frontal chest radiographs. This malposition, in association with stress-induced thymic atrophy and hyperinflated lungs, results in the apparent narrowing of the superior mediastinum on radiographs, the most consistent sign of transposition of the great arteries. The cardiovascular silhouette varies from normal in the first few days after birth to enlarged and globular, with the classic appearance described as an egg on a string (Fig 1). The right atrial border is abnormally convex, and the left atrium commonly is enlarged because of increased pulmonary blood flow. The appearance of the enlarged heart at chest radiography also has been likened to the profile of an egg on its side (1–3). The specific radiologic features are determined by the extent to which the great arteries are superposed in the plane of imaging, the size of the communication between the pulmonary and the systemic circulation, and the presence and severity of obstruction to pulmonary flow.
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Figure 1a. Transposition of the great arteries compared with normal anatomy. (a) Chest radiograph obtained in a neonate shows narrowing of the superior mediastinum, enlargement of the cardiac silhouette with abnormal convexity of the right atrial border, and increased vascular flow—typical features of transposition of the great arteries. (b) Same image as a with a superimposed drawing shows the characteristic cardiomediastinal silhouette: the egg-on-a-string sign. (c) Chest radiograph obtained in another neonate shows the normal appearance of the mediastinum, with a normal thymic shadow. (d) Drawing shows the pattern of blood flow (arrows) through the heart with transposition of the great arteries. The aorta (1) arises from the right ventricle (2), and the pulmonary artery (3) arises from the left ventricle (4). Communication between the systemic and the pulmonary circulation—an interatrial septal defect (5), an interventricular septal defect (6), or both—sustains life by allowing oxygenated blood from the left atrium (7) to mix with deoxygenated blood from the right atrium (8) before it flows via the right ventricle to the aorta and via the left ventricle to the pulmonary artery.
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Figure 1b. Transposition of the great arteries compared with normal anatomy. (a) Chest radiograph obtained in a neonate shows narrowing of the superior mediastinum, enlargement of the cardiac silhouette with abnormal convexity of the right atrial border, and increased vascular flow—typical features of transposition of the great arteries. (b) Same image as a with a superimposed drawing shows the characteristic cardiomediastinal silhouette: the egg-on-a-string sign. (c) Chest radiograph obtained in another neonate shows the normal appearance of the mediastinum, with a normal thymic shadow. (d) Drawing shows the pattern of blood flow (arrows) through the heart with transposition of the great arteries. The aorta (1) arises from the right ventricle (2), and the pulmonary artery (3) arises from the left ventricle (4). Communication between the systemic and the pulmonary circulation—an interatrial septal defect (5), an interventricular septal defect (6), or both—sustains life by allowing oxygenated blood from the left atrium (7) to mix with deoxygenated blood from the right atrium (8) before it flows via the right ventricle to the aorta and via the left ventricle to the pulmonary artery.
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Figure 1c. Transposition of the great arteries compared with normal anatomy. (a) Chest radiograph obtained in a neonate shows narrowing of the superior mediastinum, enlargement of the cardiac silhouette with abnormal convexity of the right atrial border, and increased vascular flow—typical features of transposition of the great arteries. (b) Same image as a with a superimposed drawing shows the characteristic cardiomediastinal silhouette: the egg-on-a-string sign. (c) Chest radiograph obtained in another neonate shows the normal appearance of the mediastinum, with a normal thymic shadow. (d) Drawing shows the pattern of blood flow (arrows) through the heart with transposition of the great arteries. The aorta (1) arises from the right ventricle (2), and the pulmonary artery (3) arises from the left ventricle (4). Communication between the systemic and the pulmonary circulation—an interatrial septal defect (5), an interventricular septal defect (6), or both—sustains life by allowing oxygenated blood from the left atrium (7) to mix with deoxygenated blood from the right atrium (8) before it flows via the right ventricle to the aorta and via the left ventricle to the pulmonary artery.
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Figure 1d. Transposition of the great arteries compared with normal anatomy. (a) Chest radiograph obtained in a neonate shows narrowing of the superior mediastinum, enlargement of the cardiac silhouette with abnormal convexity of the right atrial border, and increased vascular flow—typical features of transposition of the great arteries. (b) Same image as a with a superimposed drawing shows the characteristic cardiomediastinal silhouette: the egg-on-a-string sign. (c) Chest radiograph obtained in another neonate shows the normal appearance of the mediastinum, with a normal thymic shadow. (d) Drawing shows the pattern of blood flow (arrows) through the heart with transposition of the great arteries. The aorta (1) arises from the right ventricle (2), and the pulmonary artery (3) arises from the left ventricle (4). Communication between the systemic and the pulmonary circulation—an interatrial septal defect (5), an interventricular septal defect (6), or both—sustains life by allowing oxygenated blood from the left atrium (7) to mix with deoxygenated blood from the right atrium (8) before it flows via the right ventricle to the aorta and via the left ventricle to the pulmonary artery.
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Transposition of the great arteries is produced by a ventriculoarterial discordance in which the aorta arises from the morphologic right ventricle and the pulmonary artery arises from the morphologic left ventricle (Fig 1d). To sustain life, a communication (eg, a patent foramen ovale, atrial septal defect, ventricular septal defect, or a combination of these) must be present between the systemic and the pulmonary circulation, in addition to systemic collateral arteries. The volume of the pulmonary flow may be normal in the first few days after birth, but it increases with closure of the ductus arteriosus. This increase may be mild to severe, depending on the size of the communication between the systemic and pulmonary vessels. In the presence of a large communication, the vessels are usually prominent. A large communication also leads to enlargement of the heart unless the shunt is balanced or impeded by an obstruction of the pulmonary artery.
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TAPVR and Snowman Sign
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TAPVR occurs when the pulmonary veins fail to drain into the left atrium and instead form an aberrant connection with some other cardiovascular structure. Such abnormalities account for approximately 2% of cardiac malformations and are best differentiated according to the site at which the anomalous pulmonary veins terminate. Four types of TAPVR thus may be defined.
In type I, the most common of the four (55% of cases), the anomalous pulmonary veins terminate at the supracardiac level. On chest radiographs, this cardiovascular anomaly resembles a snowman:
The dilated vertical vein on the left, the innominate vein on the top, and the superior vena cava on the right form the head of the snowman; the body of the snowman is formed by the enlarged right atrium. Typically, four anomalous pulmonary veins (two from each lung) converge directly behind the left atrium and form a common vein, known as the vertical vein, that passes anterior to the left pulmonary artery and the left main bronchus to join the innominate vein (Fig 2). Less commonly, anomalous drainage to the left brachiocephalic vein, the right superior vena cava, or the azygos vein occurs. Venous obstruction in type I TAPVR is uncommon, but extrinsic obstruction may occur if the vertical vein courses between the left pulmonary artery anteriorly and the left main bronchus posteriorly.
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Figure 2a. Type I TAPVR. (a, b) Chest radiograph obtained in a neonate (b the same as a with a superimposed drawing) reveals the classic snowman sign, sometimes referred to as a figure-of-eight sign. (c) Drawing shows the return flow of venous blood (arrows). Instead of draining into the left atrium (1), the pulmonary veins (2, 3) converge behind the heart to form a common pulmonary vein (4) that connects to the vertical vein (5), which joins the left innominate vein (6). The left innominate vein drains into the superior vena cava (7). Since all of the systemic and pulmonary venous blood enters the right heart, survival is maintained by a right-to-left shunt through a communication at the level of the atrial septum (8). 9 = right atrium, 10 = right ventricle, 11 = left ventricle. (d) Frontal view obtained with angiocardiography in a neonate shows the aberrant cardiovascular anatomy: The upper left heart is bordered by the vertical vein; the superior part of the heart, by the left innominate vein; and the upper part of the right heart, by the dilated superior vena cava.
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Figure 2b. Type I TAPVR. (a, b) Chest radiograph obtained in a neonate (b the same as a with a superimposed drawing) reveals the classic snowman sign, sometimes referred to as a figure-of-eight sign. (c) Drawing shows the return flow of venous blood (arrows). Instead of draining into the left atrium (1), the pulmonary veins (2, 3) converge behind the heart to form a common pulmonary vein (4) that connects to the vertical vein (5), which joins the left innominate vein (6). The left innominate vein drains into the superior vena cava (7). Since all of the systemic and pulmonary venous blood enters the right heart, survival is maintained by a right-to-left shunt through a communication at the level of the atrial septum (8). 9 = right atrium, 10 = right ventricle, 11 = left ventricle. (d) Frontal view obtained with angiocardiography in a neonate shows the aberrant cardiovascular anatomy: The upper left heart is bordered by the vertical vein; the superior part of the heart, by the left innominate vein; and the upper part of the right heart, by the dilated superior vena cava.
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Figure 2c. Type I TAPVR. (a, b) Chest radiograph obtained in a neonate (b the same as a with a superimposed drawing) reveals the classic snowman sign, sometimes referred to as a figure-of-eight sign. (c) Drawing shows the return flow of venous blood (arrows). Instead of draining into the left atrium (1), the pulmonary veins (2, 3) converge behind the heart to form a common pulmonary vein (4) that connects to the vertical vein (5), which joins the left innominate vein (6). The left innominate vein drains into the superior vena cava (7). Since all of the systemic and pulmonary venous blood enters the right heart, survival is maintained by a right-to-left shunt through a communication at the level of the atrial septum (8). 9 = right atrium, 10 = right ventricle, 11 = left ventricle. (d) Frontal view obtained with angiocardiography in a neonate shows the aberrant cardiovascular anatomy: The upper left heart is bordered by the vertical vein; the superior part of the heart, by the left innominate vein; and the upper part of the right heart, by the dilated superior vena cava.
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Figure 2d. Type I TAPVR. (a, b) Chest radiograph obtained in a neonate (b the same as a with a superimposed drawing) reveals the classic snowman sign, sometimes referred to as a figure-of-eight sign. (c) Drawing shows the return flow of venous blood (arrows). Instead of draining into the left atrium (1), the pulmonary veins (2, 3) converge behind the heart to form a common pulmonary vein (4) that connects to the vertical vein (5), which joins the left innominate vein (6). The left innominate vein drains into the superior vena cava (7). Since all of the systemic and pulmonary venous blood enters the right heart, survival is maintained by a right-to-left shunt through a communication at the level of the atrial septum (8). 9 = right atrium, 10 = right ventricle, 11 = left ventricle. (d) Frontal view obtained with angiocardiography in a neonate shows the aberrant cardiovascular anatomy: The upper left heart is bordered by the vertical vein; the superior part of the heart, by the left innominate vein; and the upper part of the right heart, by the dilated superior vena cava.
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Type II TAPVR (30% of cases) involves a pulmonary venous connection at the cardiac level. The pulmonary veins join either the coronary sinus or the right atrium.
Type III TAPVR (13% of cases) involves a connection at the infracardiac or infradiaphragmatic level. The pulmonary veins join behind the left atrium to form a common vertical descending vein, which courses anterior to the esophagus and passes through the diaphragm at the esophageal hiatus. This vertical vein usually joins the portal venous system but occasionally connects directly to the ductus venosus, the hepatic veins, or the inferior vena cava. Type III TAPVR is virtually always accompanied by some degree of obstructed venous return. The obstruction of pulmonary venous flow causes cyanosis and, often, early and severe congestive heart failure. In addition, lymphangiectasia sometimes results from the obstruction of venous return through the vein that extends below the diaphragm. The heart size is usually normal, but there is severe interstitial pulmonary edema, thymic atrophy, and depression of the diaphragm.
Type IV TAPVR involves anomalous venous connections at two or more levels. In the most common pattern, the vertical vein drains into the left innominate vein, and the anomalous vein or veins from the right lung drain into either the right atrium or the coronary sinus. This pattern generally is associated with other major cardiac lesions.
The radiologic appearance of TAPVR varies according to the site of abnormal venous drainage and whether the flow is obstructed. The structure in which the anomalous vein terminates appears dilated; termination at the level of the coronary sinus, superior vena cava, or azygos vein leads to dilatation of that structure and produces characteristic abnormalities in the imaging appearance. All the systemic venous and pulmonary venous blood enters the right heart, and the only path for its exit to the left heart is a communication in the atrial septum, usually a large atrial septal defect or patent foramen ovale. This right-to-left shunt is essential for survival. The right heart is prominent in TAPVR because of the increased flow volume, but the left atrium remains normal in size.
In infants affected by TAPVR, cyanosis and congestive heart failure typically develop in the early neonatal period. Approximately one-third of those with TAPVR also have other associated cardiac lesions; many have heterotaxy syndrome, particularly asplenia (1–8).
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Partial Anomalous Pulmonary Venous Return and Scimitar Sign
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The scimitar sign is produced by an anomalous pulmonary vein that drains any or all of the lobes of the right lung. The so-called scimitar vein curves outward along the right cardiac border, usually from the middle of the lung to the cardio-phrenic angle, and usually empties into the inferior vena cava but also may drain into the portal vein, hepatic vein, or right atrium (Fig 3). Although the diameter of the scimitar vein depends on whether it drains the entire right lung or only a portion of it, the diameter generally increases as the vein descends. The characteristic appearance of the vein has led to its comparison to a scimitar, a sword with a curved blade that traditionally was used by Persian and Turkish warriors.
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Figure 3a. Partial anomalous pulmonary venous return. (a, b) Chest radiograph obtained in a patient with a heart murmur (b the same as a with a superimposed drawing) demonstrates a prominent curvilinear opacity that extends downward from the right hilum: the scimitar sign. (c) Drawing shows the pattern of blood flow (arrows). The luminal diameter of the scimitar vein (1), which may drain all or part of the right lung (2), enlarges as the vein descends below the diaphragm (3) to empty into the inferior vena cava (4). Occasionally, the vein may empty directly into the right atrium (5).(Reference 23). <
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Figure 3b. Partial anomalous pulmonary venous return. (a, b) Chest radiograph obtained in a patient with a heart murmur (b the same as a with a superimposed drawing) demonstrates a prominent curvilinear opacity that extends downward from the right hilum: the scimitar sign. (c) Drawing shows the pattern of blood flow (arrows). The luminal diameter of the scimitar vein (1), which may drain all or part of the right lung (2), enlarges as the vein descends below the diaphragm (3) to empty into the inferior vena cava (4). Occasionally, the vein may empty directly into the right atrium (5).(Reference 23).
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Figure 3c. Partial anomalous pulmonary venous return. (a, b) Chest radiograph obtained in a patient with a heart murmur (b the same as a with a superimposed drawing) demonstrates a prominent curvilinear opacity that extends downward from the right hilum: the scimitar sign. (c) Drawing shows the pattern of blood flow (arrows). The luminal diameter of the scimitar vein (1), which may drain all or part of the right lung (2), enlarges as the vein descends below the diaphragm (3) to empty into the inferior vena cava (4). Occasionally, the vein may empty directly into the right atrium (5).(Reference 23).
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The scimitar vein is one of the components of scimitar syndrome, which is characterized by the following additional features: (a) hypoplasia of the right lung with dextroposition of the heart, (b) hypoplasia of the right pulmonary artery, and (c) anomalous arterial supply of the right lower lobe from the abdominal aorta. Scimitar syndrome occurs almost exclusively on the right side; only one case on the left side is reported in the literature. Flow through the scimitar vein produces a left-to-right shunt that is usually hemodynamically insignificant. When the entire right lung is drained by the anomalous vein, the main pulmonary arteries become slightly enlarged (9–13). Many patients with a scimitar vein are asymptomatic and have a normal or near-normal life span. Symptoms generally do not occur unless 50% or more of the pulmonary flow shifts from the left to the right. Moreover, symptomatic patients do not become cyanotic unless pulmonary artery hypertension (a late-stage development) occurs. In some cases, ligation or coil embolization of the scimitar vein may relieve symptoms.
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Endocardial Cushion Defects and Gooseneck Sign
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The gooseneck sign, visible at left ventricular angiography, is caused by an endocardial cushion defect (Fig 4). Endocardial cushion defects, which account for 4% of all cases of congenital heart disease, comprise a spectrum of cardiac anomalies that result from interruption of the normal development of the endocardial tissues during gestation. The endocardial cushion normally forms the lower portion of the atrial septum, the upper portion of the interventricular septum, and the septal leaflets of the mitral valve and the tricuspid valve. The gooseneck-shaped deformity in endocardial cushion defect is caused by a deficiency of both the conus and sinus portions of the interventricular septum, with narrowing of the left ventricular outflow tract. The concavity of the interventricular septum below the mitral valve, along with the elongation and narrowing of the left ventricular outflow tract, produces a characteristic shape that has been compared to a sitting goose with an elongated neck on the anteroposterior projection in left ventricular angiography (14–18).
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Figure 4a. Endocardial cushion defect. (a, b) Lateral view obtained with angiocardiography (b the same as a with a superimposed drawing) shows shortening of the left ventricular inflow tract and elongation and narrowing of the left ventricular out-flow tract, which together produce the characteristic gooseneck sign. (c) Drawing (anteroposterior view) of an endocardial cushion defect shows the concavity of the medial margin of the left ventricle (1) below the mitral valve and resultant narrowing of the left ventricular outflow tract (2).
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Figure 4b. Endocardial cushion defect. (a, b) Lateral view obtained with angiocardiography (b the same as a with a superimposed drawing) shows shortening of the left ventricular inflow tract and elongation and narrowing of the left ventricular out-flow tract, which together produce the characteristic gooseneck sign. (c) Drawing (anteroposterior view) of an endocardial cushion defect shows the concavity of the medial margin of the left ventricle (1) below the mitral valve and resultant narrowing of the left ventricular outflow tract (2).
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Figure 4c. Endocardial cushion defect. (a, b) Lateral view obtained with angiocardiography (b the same as a with a superimposed drawing) shows shortening of the left ventricular inflow tract and elongation and narrowing of the left ventricular out-flow tract, which together produce the characteristic gooseneck sign. (c) Drawing (anteroposterior view) of an endocardial cushion defect shows the concavity of the medial margin of the left ventricle (1) below the mitral valve and resultant narrowing of the left ventricular outflow tract (2).
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Tetralogy of Fallot and Boot-shaped Heart
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The four established components of tetralogy of Fallot, which was first described in 1888 by French physician Etienne-Louis Arthur Fallot, include (a) ventricular septal defect, (b) infundibular pulmonary stenosis, (c) overriding aorta, and (d) right ventricular hypertrophy. The current understanding of the embryologic origin of this syndrome is that it results from a single defect, an anterior malalignment of the conal septum, which in turn causes ventricular septal defect, right ventricular outflow tract obstruction, and overriding aorta. Right ventricular hypertrophy typically develops in long-standing untreated disease. Tetralogy of Fallot accounts for 10%–11% of cases of congenital heart disease.
On chest radiographs in those affected by this syndrome, the heart has the shape of a wooden shoe or boot (in French, coeur en sabot) (Fig 5). This deformity is due to uplifting of the cardiac apex because of right ventricular hypertrophy and concavity of the main pulmonary artery. The shadow of the pulmonary arterial trunk is almost invariably absent, and blood flow to the lungs is usually reduced. The right ventricular infundibulum often forms a slight bulge in the upper left heart border, while the middle left heart border is usually concave. Approximately 25% of those affected by tetralogy of Fallot have a right-sided aortic arch (1–4,19) (Fig 5a). Overall, the most common radiologic finding in tetralogy of Fallot is an upturned cardiac apex, and the more severe the obstruction of the right ventricular outflow tract, the more pronounced that deformity.
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Figure 5a. Tetralogy of Fallot. (a, b) Chest radiograph obtained in an infant with a right-sided aortic arch (b the same as a with a superimposed drawing) shows the characteristic boot-shaped sign produced by upturning of the cardiac apex because of right ventricular hypertrophy and by the concavity of the main pulmonary artery. (c) Drawing depicts the pattern of blood flow (arrows) with the characteristic ventricular septal defect (1), infundibular pulmonary stenosis (2), overriding aorta (3), and right ventricular hypertrophy (4). The oxygen-rich blood in the left side of the heart (5) mixes with oxygen-poor blood in the right side of the heart (6) before it proceeds to the aorta (7).
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Figure 5b. Tetralogy of Fallot. (a, b) Chest radiograph obtained in an infant with a right-sided aortic arch (b the same as a with a superimposed drawing) shows the characteristic boot-shaped sign produced by upturning of the cardiac apex because of right ventricular hypertrophy and by the concavity of the main pulmonary artery. (c) Drawing depicts the pattern of blood flow (arrows) with the characteristic ventricular septal defect (1), infundibular pulmonary stenosis (2), overriding aorta (3), and right ventricular hypertrophy (4). The oxygen-rich blood in the left side of the heart (5) mixes with oxygen-poor blood in the right side of the heart (6) before it proceeds to the aorta (7).
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Figure 5c. Tetralogy of Fallot. (a, b) Chest radiograph obtained in an infant with a right-sided aortic arch (b the same as a with a superimposed drawing) shows the characteristic boot-shaped sign produced by upturning of the cardiac apex because of right ventricular hypertrophy and by the concavity of the main pulmonary artery. (c) Drawing depicts the pattern of blood flow (arrows) with the characteristic ventricular septal defect (1), infundibular pulmonary stenosis (2), overriding aorta (3), and right ventricular hypertrophy (4). The oxygen-rich blood in the left side of the heart (5) mixes with oxygen-poor blood in the right side of the heart (6) before it proceeds to the aorta (7).
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Aortic Coarctation, Figure of Three, and Reverse Figure of Three
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Coarctation of the aorta is produced by a deformity of the aortic media and intima, which causes a prominent posterior infolding of the aortic lumen. This deformity characteristically occurs at or near the junction of the aortic arch and the descending thoracic aorta. Infolding may extend laterally and cause eccentric narrowing of the lumen at the level where the ductus or ligamentum arteriosus inserts anteromedially. Luminal narrowing in turn obstructs the flow of blood from the left ventricle. Cystic medial necrosis is a common occurrence at the level of coarctation, and intimal thickening and elastic tissue disruption often develop distal to the site; these conditions may predispose the aorta to infective endarteritis, intimal dissection, and aneurysm.
Coarctation of the aorta accounts for 5%–10% of congenital cardiac lesions and is usually sporadic. However, it occurs with increased frequency among patients with Turner syndrome, 20%–36% of whom are affected. Clinical manifestations vary from congestive heart failure in infancy to hypertension with differential pressures between the upper and lower extremities in adulthood.
Two classic radiologic signs associated with aortic coarctation are the figure-of-three sign and the reverse figure-of-three sign. The aortic segment affected by coarctation has a shape that resembles the number 3 on frontal chest radiographs (Fig 6a–6d). The number3 is formed by dilatation of the left subclavian artery and aorta proximal to the site of coarctation, indentation of the site, and dilatation of the aorta distal to the site. This sign is seen in 50%–66% of adults with aortic coarctation. The reverse figure-of-three sign, a mirror image of the number 3, is observed on the left anterior oblique view during barium esophagography in patients with aortic coarctation (Fig 6e, 6f).
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Figure 6a. Aortic coarctation with associated rib notching. (a, b) Frontal view (a) and close-up frontal view (b) obtained with chest radiography in a young man with hypertension show the figure-of-three sign formed by prestenotic and poststenotic dilatation of the aorta, with an intervening indentation at the site of coarctation and with bilateral rib notching caused by pressure from intercostal blood vessels. (c, d) Chest radiograph in a child (d the same as c with a superimposed 3) shows clear rib notching despite less pronounced coarctation. (e, f) Left anterior oblique view of the chest, obtained with barium esophagography (b the same as a with a superimposed reversed 3), shows an indentation in the esophageal contour because of pressure from the coarctated aorta.
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Figure 6b. Aortic coarctation with associated rib notching. (a, b) Frontal view (a) and close-up frontal view (b) obtained with chest radiography in a young man with hypertension show the figure-of-three sign formed by prestenotic and poststenotic dilatation of the aorta, with an intervening indentation at the site of coarctation and with bilateral rib notching caused by pressure from intercostal blood vessels. (c, d) Chest radiograph in a child (d the same as c with a superimposed 3) shows clear rib notching despite less pronounced coarctation. (e, f) Left anterior oblique view of the chest, obtained with barium esophagography (b the same as a with a superimposed reversed 3), shows an indentation in the esophageal contour because of pressure from the coarctated aorta.
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Figure 6c. Aortic coarctation with associated rib notching. (a, b) Frontal view (a) and close-up frontal view (b) obtained with chest radiography in a young man with hypertension show the figure-of-three sign formed by prestenotic and poststenotic dilatation of the aorta, with an intervening indentation at the site of coarctation and with bilateral rib notching caused by pressure from intercostal blood vessels. (c, d) Chest radiograph in a child (d the same as c with a superimposed 3) shows clear rib notching despite less pronounced coarctation. (e, f) Left anterior oblique view of the chest, obtained with barium esophagography (b the same as a with a superimposed reversed 3), shows an indentation in the esophageal contour because of pressure from the coarctated aorta.
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Figure 6d. Aortic coarctation with associated rib notching. (a, b) Frontal view (a) and close-up frontal view (b) obtained with chest radiography in a young man with hypertension show the figure-of-three sign formed by prestenotic and poststenotic dilatation of the aorta, with an intervening indentation at the site of coarctation and with bilateral rib notching caused by pressure from intercostal blood vessels. (c, d) Chest radiograph in a child (d the same as c with a superimposed 3) shows clear rib notching despite less pronounced coarctation. (e, f) Left anterior oblique view of the chest, obtained with barium esophagography (b the same as a with a superimposed reversed 3), shows an indentation in the esophageal contour because of pressure from the coarctated aorta.
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Figure 6e. Aortic coarctation with associated rib notching. (a, b) Frontal view (a) and close-up frontal view (b) obtained with chest radiography in a young man with hypertension show the figure-of-three sign formed by prestenotic and poststenotic dilatation of the aorta, with an intervening indentation at the site of coarctation and with bilateral rib notching caused by pressure from intercostal blood vessels. (c, d) Chest radiograph in a child (d the same as c with a superimposed 3) shows clear rib notching despite less pronounced coarctation. (e, f) Left anterior oblique view of the chest, obtained with barium esophagography (b the same as a with a superimposed reversed 3), shows an indentation in the esophageal contour because of pressure from the coarctated aorta.
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Figure 6f. Aortic coarctation with associated rib notching. (a, b) Frontal view (a) and close-up frontal view (b) obtained with chest radiography in a young man with hypertension show the figure-of-three sign formed by prestenotic and poststenotic dilatation of the aorta, with an intervening indentation at the site of coarctation and with bilateral rib notching caused by pressure from intercostal blood vessels. (c, d) Chest radiograph in a child (d the same as c with a superimposed 3) shows clear rib notching despite less pronounced coarctation. (e, f) Left anterior oblique view of the chest, obtained with barium esophagography (b the same as a with a superimposed reversed 3), shows an indentation in the esophageal contour because of pressure from the coarctated aorta.
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There are two main types of aortic coarctation: localized coarctation and tubular hypoplasia. Localized aortic coarctation, also known as postductal or adult-type coarctation, is the most common type. It is characterized by a focal narrowing of the aorta, almost always at a site just beyond the origin of the left subclavian artery or the ligamentum arteriosum (Fig 7). This deformity of the external contour of the aorta is accompanied by dilatation of the left subclavian artery. An elaborate system of collateral vessels (including collateral internal mammary, intercostal, and superior epigastric arteries) forms to bypass the coarctation. The dilated and tortuous intercostal vessels form deep grooves on the undersurfaces of the ribs (a process known as rib notching)—usually the third or fourth through the eighth ribs (Figs 6c, 6d). Since the first two intercostal arteries are supplied by the costocervical trunk instead of by the descending thoracic aorta, the first two intercostal arteries do not serve as collateral pathways, and therefore the first and second ribs do not demonstrate notching. The pulmonary flow is normal unless left ventricular decompensation has occurred (3,4,20,21).
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Figure 7. Localized (postductal or adult-type) aortic coarctation. Drawing shows a focal constriction of the aorta (1) just beyond the origin of the left subclavian artery (2) and the ligamentum arteriosum (3). The contour of the aorta is deformed by both pre- and poststenotic dilatation, and the left subclavian artery is dilated. 4 = left common carotid artery, 5 = innominate artery, 6 = right heart structures, 7 = left heart structures, 8 = pulmonary artery.
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Tubular hypoplasia, which also is known as preductal or infantile-type coarctation, is the second most common cause of heart failure in newborns. In this type of coarctation, a long aortic segment beyond the origin of the innominate artery is narrowed (Fig 8). This abnormality is combined with a superimposed focal constriction before the level of the ductus arteriosus. This type of aortic coarctation usually is associated with an intracardiac defect, especially a deformed or bicuspid aortic valve.
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Figure 8. Tubular hypoplasia (preductal or infantile-type aortic coarctation). Drawing shows a focal constriction of the aorta (1) above the level of the ductus arteriosus (2) and a lengthy narrowed segment of the aortic arch (3) after the origin of the innominate artery (4). 5 = left common carotid artery, 6 = left subclavian artery, 7 = right heart structures, 8 = left heart structures, 9 = pulmonary artery.
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Ebstein Anomaly and Box-shaped Heart
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Ebstein anomaly, first described by German physician Wilhelm Ebstein in 1866, accounts for 0.5%–0.7% of cases of congenital heart disease. A strong association has been reported between this abnormality and oral lithium therapy during pregnancy. Ebstein anomaly is the only cyanotic congenital malformation of the heart in which both the aorta and the pulmonary trunk are smaller than normal. The pulmonary flow may vary from normal to borderline to diminished. If it is normal, the patient is usually acyanotic; if it is borderline or diminished, the patient is usually cyanotic.
Ebstein anomaly is characterized by the downward displacement of the septal leaflets and posterior leaflets of the tricuspid valve into the inflow portion of the right ventricle. This displacement results in the formation of a common right ventriculoatrial chamber and causes tricuspid regurgitation. Insufficiency of the tricuspid valve leads to dilatation of the right ventricular outflow tract and all proximal right heart structures, which in turn leads to even greater tricuspid insufficiency. The right atrium becomes enlarged, and a right-to-left shunt (through a patent foramen ovale or atrial septal defect) is seen in most patients. Cyanosis is caused primarily by the right-to-left shunt, and increased right atrial pressure causes a greater right-to-left shunt and more severe cyanosis.
The most consistent imaging feature is right atrial enlargement; the right atrium may be huge and fill the entire right hemithorax. The left atrium is normal in size, but the left cardiac contour has a shelved appearance because of the dilated right ventricular outflow tract (1–4,8,22–26). The aorta is small, and the pulmonary trunk, which normally appears as a discrete convex bulge, is absent. This combination of features produces a cardiac silhouette that has been described as box shaped (Fig 9).
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Figure 9a. Ebstein anomaly. (a, b) Frontal (a) and lateral (b) views obtained with chest radiography in an infant show massive cardiomegaly with decreased pulmonary flow. (c) Frontal view (same as a with a superimposed drawing) best depicts the box-shaped heart, an appearance caused by enlargement of the right atrium and hypoplasia of the pulmonary trunk. (d) Drawing shows the pattern of blood flow (arrows) caused by downward displacement of the tricuspid valve (1), with resultant formation of a common chamber (3) consisting of the right ventricle (2) and the dilated right atrium (4), and by the right-to-left shunt of blood through a defect at the atrial level (5). 6 = left atrium, 7 = left ventricle, 8 = aorta, 9 = pulmonary artery.
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Figure 9b. Ebstein anomaly. (a, b) Frontal (a) and lateral (b) views obtained with chest radiography in an infant show massive cardiomegaly with decreased pulmonary flow. (c) Frontal view (same as a with a superimposed drawing) best depicts the box-shaped heart, an appearance caused by enlargement of the right atrium and hypoplasia of the pulmonary trunk. (d) Drawing shows the pattern of blood flow (arrows) caused by downward displacement of the tricuspid valve (1), with resultant formation of a common chamber (3) consisting of the right ventricle (2) and the dilated right atrium (4), and by the right-to-left shunt of blood through a defect at the atrial level (5). 6 = left atrium, 7 = left ventricle, 8 = aorta, 9 = pulmonary artery.
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Figure 9c. Ebstein anomaly. (a, b) Frontal (a) and lateral (b) views obtained with chest radiography in an infant show massive cardiomegaly with decreased pulmonary flow. (c) Frontal view (same as a with a superimposed drawing) best depicts the box-shaped heart, an appearance caused by enlargement of the right atrium and hypoplasia of the pulmonary trunk. (d) Drawing shows the pattern of blood flow (arrows) caused by downward displacement of the tricuspid valve (1), with resultant formation of a common chamber (3) consisting of the right ventricle (2) and the dilated right atrium (4), and by the right-to-left shunt of blood through a defect at the atrial level (5). 6 = left atrium, 7 = left ventricle, 8 = aorta, 9 = pulmonary artery.
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Figure 9d. Ebstein anomaly. (a, b) Frontal (a) and lateral (b) views obtained with chest radiography in an infant show massive cardiomegaly with decreased pulmonary flow. (c) Frontal view (same as a with a superimposed drawing) best depicts the box-shaped heart, an appearance caused by enlargement of the right atrium and hypoplasia of the pulmonary trunk. (d) Drawing shows the pattern of blood flow (arrows) caused by downward displacement of the tricuspid valve (1), with resultant formation of a common chamber (3) consisting of the right ventricle (2) and the dilated right atrium (4), and by the right-to-left shunt of blood through a defect at the atrial level (5). 6 = left atrium, 7 = left ventricle, 8 = aorta, 9 = pulmonary artery.
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Summary
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The field of cardiovascular imaging is rapidly expanding, and it is important that radiologists be familiar with the classic signs of congenital cardiovascular abnormalities in both pediatric and adult patients. An understanding of the origin and pathophysiologic significance of each of these signs is essential in daily radiologic practice.
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Footnotes
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Abbreviations: TAPVR = total anomalous pulmonary venous return
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References
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M. S. Parker, M. H. Chasen, and N. Paul
Radiologic Signs in Thoracic Imaging: Case-Based Review and Self-Assessment Module
Am. J. Roentgenol.,
March 1, 2009;
192(3_Supplement):
S34 - S48.
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Abstract
LEARNING OBJECTIVES
