Noncoronary CT angiography of the heart is performed with a pulmonary embolism protocol using thin collimation (<1 mm), pitch 1.0 to 1.5, weight-based low-dose milliamperage, and the lowest possible kilovoltage. Studies are performed with nonionic contrast agent, which is administered with a power injector, whenever possible. The flow rate for 2-g catheters is 2 to 2.5 mL per second, and the flow rate for 20-g catheters is 3 to 4 mL per second. Scan delay time is determined with an automatic bolus tracking system using a variable region of interest, depending on the clinical suspicion, and a threshold level of 100 to 120 Hounsfield units (HU) for triggering the scan. Scans are performed in a craniocaudal direction during a single breath-hold in cooperative patients. In patients who are unable to suspend respiration, scans are acquired during quiet respiration.

Electrocardiographic (ECG) gating is usually not needed for the evaluation of congenital and acquired (noncoronary) cardiac abnormalities. The volumetric data are reconstructed at 3- to 5-mm slice thickness for routine viewing and at 1 to 2 mm for multiplanar reformatting and 3D reconstructions. A standard reconstruction algorithm is used for reconstruction.

For adequate visualization of the coronary arterial tree and associated abnormalities, isotropic (i.e., equal voxel dimensions in x, y, and z axes) or near-isotropic in-plane and through-plane spatial resolutions of <1 mm are necessary. Coronary artery CT is performed with submillimter collimation, pitch <1 (0.2 to 0.3), slice thickness <1 mm, and overlapping reconstructions (30% to 50% overlap). High milliamperage and kilovoltage are required. Automatic bolus tracking or a test bolus technique is used to trigger coronary CT angiography (CTA) (10).

Gating is necessary for coronary artery CTA to acquire motionfree images. Coronary artery CTA is usually performed using retrospective ECG gating. Data from specific points in the cardiac cycle, usually during diastole, are then retrospectively referenced to the ECG signal for image reconstruction. Gating is most efficient when the heart rate is <90, but acceptable-quality images can occasionally be obtained at higher heart rates. An important disadvantage of ECG-gated imaging is the higher radiation exposure. Online dose modulation programs can minimize radiation dose via ECG pulsing, which uses high tube current only during diastole, when images are most likely to be reconstructed. Tube current is reduced during systole. Maximum-intensity projection images, curved multiplanar reformations, and volume renderings have proved useful for evaluation of complex anatomy and anomalies (10).

The right atrium consists of a larger quadrangular posterior cavity and a smaller, triangular anterior appendage. The left atrium consists of a larger cuboidal posterior cavity and smaller narrow anterior appendage. The right atrium is divided into the right atrium proper and the right atrial appendage by a vertical muscle ridge, known as the crista terminalis, which extends along the posterolateral aspect of the right atrium. The left atrium contains the ligament of Marshall, also known as the oblique vein of the left atrium. This vein indents the left atrium between the left upper pulmonary vein and left atrial appendage and has attenuation similar to myocardium (Fig, 5.5).

The atria are separated by the interatrial septum. Within the atrial septum is the fossa ovale, which is the thinnest part of the septum and lies in the mid to lower part of the septum. A small slitlike opening may be present in the fossa ovale, termed a patent foramen ovale (see section below on atrial septal defects).

The right ventricle is characterized by coarse trabeculae, which are muscular columns projecting into the ventricular cavity. A commonly identified muscle band is the
moderator band, which extends from the ventricular septum to the right ventricle free wall. The left ventricle is longer than the right and is characterized by fine trabeculation. Because of the fine trabeculae (i.e., fine muscular projections), the endocardial surface of the left ventricle is smoother than that of the right. The left ventricle has two prominent papillary muscles, the anterior lateral and the posterior medial, which arise from the free wall surface (Fig. 5.6) (3).

The right and left ventricles are separated by the interventricular septum (Fig. 5.6). The upper and lower parts of the septum are relatively thin and fibrous and termed
the membranous ventricular septum. The remaining middle part of the septum is thick and muscular and termed the muscular ventricular septum.

The aortic valve has right, left and noncoronary cusps. The pulmonic valve has right, left, and anterior cusps (Fig. 5.7). The mitral valve has aortic (anterior) and mural (posterior) leaflets. The tricuspid valve has septal, anterior, and posterior leaflets.

The left main coronary artery arises from the left coronary sinus and courses posterior to the pulmonary truck. It bifurcates into the left anterior descending (LAD) and left circumflex (LCX) arteries. The right coronary artery (RCA) arises from the right coronary sinus and passes to the right and posterior to the pulmonary outflow tract and then inferiorly in the right atrioventricular groove. It provides atrial branches (to the right atrium) and marginal branches (to the right ventricle) (Fig. 5.8). The cardiac veins drain into the coronary sinus, which opens into the right atrium.

Coarctation of the aorta accounts for 5% to 8% of all congenital cardiac disease (11). Two main types of coarctation are recognized: preductal (also known as the infantile form) and postductal (adult form). In preductal coarctation, the narrowing is just above the origin of the left subclavian artery near the ligamentum arteriosum (Fig. 5.9). Preductal coarctation is associated with long-segment narrowing of the aortic arch and other congenital heart diseases, including ventricular septal defect, patent ductus arteriosus, and hypoplastic left heart. Collateral vessel formation is usually absent. Affected patients present in the first 6 months of life with heart failure.

In postductal coarctation, the site of narrowing is distal to the left subclavian artery. The CT findings are short-segment aortic narrowing with an infolding or shelflike appearance of the posterior wall, aortic dilatation proximal and distal to the coarctation, and collateral vessel formation (Fig. 5.10) (12). The intercostal arteries (usually third through eighth) and internal thoracic arteries act as collateral pathways. Patients are usually asymptomatic, and the condition is recognized during evaluation of hypertension or a coexistent cardiac anomaly, commonly a bicuspid aortic valve.

Treatment for coarctation is either open surgical repair, such as prosthetic patch aortoplasty and end-to-end anastomosis or catheter interventions, including balloon angioplasty and stent implantation (13,14). The choice of procedure depends on the site and extent of the coarctation and the patient's age. After surgical repair or angioplasty, CT can be used to demonstrate complications, including residual stenosis or restenosis, aneurysm formation, dissection, and rarely, rupture (11) (Fig. 5.11).

Interruption of the aortic arch is a rare anomaly, accounting for about 1.5% of congenital heart disease (15). There are three types of interrupted arch based on the site of interruption. In descending order of frequency, these are the following: Type A, interruption distal to the left subclavian artery; Type B, interruption between the left common carotid artery and the left subclavian artery; and Type C, interruption between the brachiocephalic trunk and the left carotid artery (15). A dilated patent ductus arteriosus supplies the descending aorta beyond the interruption (16,17) (Fig. 5.12). Patients present in the early neonatal period with respiratory distress, cyanosis, and congestive heart failure. Associated cardiac defects include ventricular septal defect, bicuspid aortic valve, aortopulmonary window, truncus arteriosus, transposition of the great arteries, double-outlet right ventricle, and single ventricle.

Hypoplastic left heart syndrome is characterized by underdevelopment of the left ventricle (18). The result is a small left ventricle and ascending aorta; the right heart and main pulmonary artery are enlarged. Atrial and ventricular septal defects and patent ductus arteriosus are common associated defects.

Treatment of hypoplastic left heart includes the Norwood procedure and heart transplantation. The three stages of the Norwood procedure are (a) atrial septectomy; (b) anastomosis of the proximal pulmonary artery to the aorta with homograft augmentation of the aortic arch, creating a neoaorta; and (c) a Fontan-type operation (18). The Fontan operation shunts blood from the right heart to the pulmonary artery (neoaorta), resulting in a single-ventricle physiology. CT usually has no role in diagnosis of this malformation, but postoperatively it can be used to evaluate the morphology of the various stages of the Norwood procedure and size of the great vessels and cardiac chambers (Fig. 5.13).

Aortic stenosis can be classified as valvular (most common), subvalvular, or supravalvular depending on the level of obstruction. Valvular stenosis is usually the result of a congenital bicuspid aortic valve. Less commonly, the valve is unicuspid or tricuspid; unicuspid and trileaflet valves are severely dysplastic and inherently stenotic at birth (19).

The bicuspid valve is usually functionally competent in children, although occasionally it may be associated with stenosis or regurgitation. It also may be associated with coarctation of the aorta and ventricular septal defect. Patients with aortic valve stenosis commonly come to clinical attention because of a murmur. CT findings include a bicuspid valve, thickened valve leaflets, poststenotic jetting of contrast or blood, poststenotic dilatation of the aorta, and left ventricular hypertrophy (Figs. 5.1 and 5.14).

Treatment of valve stenosis has included percutaneous balloon valvuloplasty, surgical valvotomy, prosthetic valve replacement, and more recently, the Ross procedure. In the Ross procedure, the stenotic aortic valve is replaced with the native pulmonary valve, annulus, and outflow trunk (autograft transplantation). The right ventricular outflow tract is reconstructed using an autograft.

Supravalvular aortic stenosis is nearly always associated with Williams syndrome (hypercalcemia, elfin facies, variable mental retardation). Congenital subvalvular stenosis can be due to a simple fibrous membrane or a tunnel-like fibromuscular band in the left ventricular outlet tract.

Pulmonary valve stenosis is most often secondary to fusion of the leaflets, resulting in a bicuspid valve with a narrowed opening at its apex. Less often, the valve is dysplastic; the leaflets are thick but not fused (20). Patients are commonly asymptomatic, and the diagnosis is suspected where there is dilatation of the pulmonary artery on plain chest radiographs. CT findings of pulmonary valve stenosis include main and left pulmonary artery dilatation, a normal-sized right pulmonary artery (Fig. 5.15), thickened valve leaflets, and right ventricular hypertrophy. Treatment is either surgical valvulotomy or balloon valvuloplasty.

Peripheral pulmonary artery stenosis is associated with congenital syndromes, including Williams, Noonan (hypertelorism, downslanting eyes, webbed neck, short stature, and pectus deformity), Alagille (jaundice in early infancy, abnormal facies, butterfly vertebrae, growth and mental retardation, and hypogonadism), and Ehlers–Danlos syndrome (joint laxity, hyperextensible skin). Patients with mild stenosis are usually asymptomatic. Patients with stenoses of multiple arteries may present with right heart failure.

Congenital absence of the pulmonic valve may be an isolated lesion or it may be associated with tetralogy of Fallot. Patients have marked pulmonic regurgitation associated with massive dilatation of the pulmonary arteries, right atrial and ventricular enlargement, and almost always a ventricular septal defect (Fig. 5.16).

Ventricular septal defect (VSD) is the most common congenital heart lesion, accounting for 20% to 25% of all congenital heart defects in children (21). VSDs may be isolated or they can be associated with other defects, such as tetralogy of Fallot, coarctation of the aorta, truncus arteriosus, and tricuspid atresia. They also are commonly associated with chromosomal disorders, including trisomies 13, 18, and 21.

VSDs are named by their location in the septum as follows: perimembranous (in the subaortic region), muscular (in the muscular septum), supracristal or outlet (below the pulmonary valve), and inlet (near the mitral and tricuspid valves and part of the atrioventricular canal defect) (Fig. 5.17). CT findings include interruption of the interventricular septum with contrast-enhanced blood in the septal defect; main, right, and left pulmonary artery enlargement; right or biventricular enlargement; and left atrial enlargement (Fig. 5.18).

Small isolated VSDs often close spontaneously. Small VSDs that fail to close spontaneously may be closed with a percutaneous septal occluder device. Large lesions are usually closed surgically with a patch graft.

Atrial septal defect (ASD) accounts for about 10% of all congenital heart defects in children (22). They usually occur in isolation, but they can be associated with the Holt–Oram syndrome (upper limb and cardiac anomalies) and mitral valve prolapse. There are four types of ASD depending on their sites: in the septum secundum (most common), sinus venosus, primum, and unroofed coronary sinus (least common) (23) (Fig. 5.19).

Secundum ASD is located in the region of the fossa ovale, which is in the midportion of the septum (Fig. 5.20). Sinus venosus is usually located high in the septum at the
ostium of the superior vena cava and is commonly associated with anomalous right upper venous return into the superior vena cava (Fig. 5.21). Less commonly, a sinus venosus ASD occurs in the lower septum, bordering the ostium of the inferior vena cava. The primum ASD is found in the lower part of the atrial septum, bordering the atrioventricular valves. It is associated with the atrioventricular canal defect (Fig. 5.22). The unroofed coronary sinus ASD results when the wall between the coronary sinus and the left atrium is fenestrated or absent. The coronary sinus is in the right atrium, but if there is a hole in the roof of the sinus, the right and left atria will be in continuity.

The CT features of atrial septal defects are discontinuity of a portion of the interatrial septum with contrast-enhanced blood seen in the defect, large pulmonary arteries, right or biatrial enlargement, and right ventricular enlargement. Transcatheter closure with a septal occluder device is the treatment for small ASDs (Fig. 5.23) (24). Surgical closure is necessary for large or multiple defects.

The differential diagnostic consideration for secundum ASD is a patent foramen ovale. The patent foramen ovale results when the valve of the foramen ovale fails to fuse with the fossa ovalis after birth. There is no structural deficiency of septal tissue. The patent foramen is small and acts like a flaplike valve. It stays closed as long as left atrial pressure is greater than right atrial pressure, but it can reopen when right atrial pressure increases, such as with a Valsalva maneuver, coughing, or sneezing. In this case, blood may flow from the right to left atrium. The CT finding is a jet of contrast crossing from the right to the
left atrium at the level of the midseptum (Fig. 5.24). The jet is small and thus often seen on only one image. Differentiation from a small atrial septal defect can be difficult.

Atrioventricular (AV) canal, also known as atrioventricular septal defect and endocardial cushion defect, is characterized by defects in the atrioventricular valves and variable involvement of the adjacent atrial and ventricular septa. This anomaly may be complete or incomplete (25). In the complete form, there is a primum ASD, inlet VSD, and a single atrioventricular valve, which allows blood to flow freely between the ventricles and the atria (Fig. 5.22). The more common incomplete AV canal is characterized by a primum ASD and a cleft mitral valve, causing varying degrees of mitral regurgitation. Occasionally there is a cleft in the tricuspid valve. There is no ventricular septal defect. Associated findings in both types of AV canal include atrial enlargement, dilated pulmonary arteries, and a small aorta. Surgical repair is patch closure of the ASD and VSD and reconstruction of the atrioventricular valve.

Patent ductus arteriosus (PDA) is defined as persistence of the ductus arteriosus beyond the functional closure that usually occurs within 24 hours of birth. The diagnosis is suspected because of a murmur on physical examination. Small PDAs also can be detected incidentally by CT (26). At CT, the PDA is seen as a tubular structure connecting the proximal descending aorta to the left pulmonary
artery near its origin (26) (Fig. 5.25). With large shunts, there is dilatation of the left atrium, left ventricle, aortic arch, and pulmonary arteries. Punctate calcification may be noted in the ligamentum arteriosum after ductal closure (Fig. 5.25C).

Infants with PDAs are treated with prostaglandin inhibitors (indomethacin), and if this fails, surgical closure with suture ligation is performed. PDAs in older children may be treated with percutaneous occluder devices.

Cardiac surgery can be reparative or palliative. Reparative surgery refers to an operation that corrects the basic abnormalities and improves physiologic consequences. Palliative surgery refers to an operation that improves pulmonary circulation but leaves the underlying malformations unchanged. The common palliative procedures are the Blalock–Taussig and Glenn shunts. Less commonly, Waterston or Potts shunts are performed.

The Blalock–Taussig shunt connects a subclavian artery to the ipsilateral pulmonary artery either directly with an end-to-side anastomosis or using an interposition tube graft (modified Blalock–Taussig shunt) (Fig. 5.26). The classic Glenn shunt connected the superior vena cava to the distal end of the divided right pulmonary artery. Acquired arteriovenous malformations with arterial desaturation were a complication of this procedure. The classic Glenn shunt has been replaced by the bidirectional Glenn shunt in which the superior vena cava is anastomosed to the undivided main pulmonary artery (Fig. 5.27). The Waterston shunt is a communication between the main pulmonary artery and the ascending aorta. The Potts shunt involves creating a communication between a pulmonary artery and the ipsilateral descending aorta. Both the Waterston and Potts shunts are complicated by the development of pulmonary vascular obstructive disease.

Tetralogy of Fallot, the most common cyanotic congenital heart defect, is characterized by subpulmonic infundibular stenosis, ventricular septal defect, an aorta that overrides the right and left ventricles, and right ventricular hypertrophy (28) (Fig. 5.28). Associated abnormalities include a right aortic arch in about 20% to 25% of patients, an atrial septal defect (termed pentalogy of Fallot) in 10%, and coronary artery anomalies in 10% (29).

Previously, patients with tetralogy of Fallot underwent a palliative procedure prior to definitive repair. At present, patients often undergo primary repair at presentation, which involves closure of the ventricular septal
defect and relief of the right ventricular outflow tract obstruction (30). Repair of the outflow tract obstruction may involve pulmonary valvotomy, resection of the infundibular muscle, or placement of a patch across the outflow tract of pulmonary valve annulus. Complications following repair include aneurysmal dilatation of the right ventricular outflow repair (Fig. 5.29), residual or recurrent obstruction of the outflow tract, residual VSD, and pulmonary regurgitation.

Pulmonary atresia can occur with or without a ventricular septal defect. Both forms are characterized by absence of the pulmonary valve and hypoplastic or absent native pulmonary arteries; the right and left pulmonary arteries may or may not communicate with each other (31). Pulmonary blood flow is via collateral arteries from the aorta; bronchial, pleural, intercostal, or coronary arteries; or a patent ductus arteriosus. CT can be useful to demonstrate the size and confluence or nonconfluence of the pulmonary arteries and the presence and number of collateral vessels (Fig. 5.30) (32).

In tricuspid atresia, there is absence of a direct communication between the right atrium and right ventricle. The
tricuspid valve and the inflow portion of the right ventricle are absent, and fatty tissue usually fills the atrioventricular groove (Fig. 5.31). The right ventricle is small. An atrial septal defect or patent foramen ovale and a ventricular septal defect are common (33). Dextrotransposition of the great vessels is present in 30% of patients, and a right-sided aortic arch in 5% to 10% of patients (34).

Patients with tricuspid atresia (i.e., univentricular circulation) are treated with a Fontan procedure, which is a palliative operation involving diversion of the systemic venous return to the pulmonary artery, bypassing the right ventricle. There are many variations of this operation. The classic or original Fontan used a valved conduit between the right atrium and the pulmonary artery. Subsequently this was converted to a direct anastomosis of the right atrium or appendage to the pulmonary artery (Fig. 5.31). The classic and modified Fontan procedures are no longer performed because they result in a dilated right atrium and atrial arrhythmias. In the extracardiac Fontan, the inferior vena cava is connected to the pulmonary artery via an extracardiac conduit. The superior vena cava is anastomosed to the main pulmonary artery as in the bidirectional Glenn shunt. In the total cavopulmonary Fontan, a baffle links the inferior vena cava and superior vena cava to each other, and it is then connected to the pulmonary artery (35) (Fig. 5.32). The total cavopulmonary and extracardiac Fontan procedures are currently the preferred methods of cavopulmonary connection.

Ebstein anomaly is characterized by displacement of the septal and posterior leaflets of the tricuspid valve into the
right ventricle with resultant atrialization of portions of the right ventricle. The anterior leaflet is usually malformed and abnormally tethered to the right ventricular free wall (36,37). The functional outlet part of the right ventricle is small (Fig. 5.33). The right atrium dilates because right ventricular function is impaired. A patent foramen ovale or secundum ASD, associated with a right to left shunt, is common (36). Patients with severe leaflet displacement present in the neonatal period with cyanosis owing to right-to-left shunting at the atrial level or right-sided heart failure. Patients with mild tricuspid leaflet displacement can have normal valvular function, and in these cases, the anomaly can be discovered incidentally on an imaging study.

Treatment for patients with more severe Ebstein anomaly is reduction and plication of the right atrial free wall and tricuspid valve reconstruction. Patients with milder malformations may need no interevention.

Dextrotransposition of the great arteries (D-TGA), also termed complete transposition, is characterized by atrioventricular concordance and ventriculoarterial discordance. The pulmonary artery arises from the morphologic left ventricle, and the aorta arises from the morphologic right ventricle. The altered origin of the great arteries results in an abnormal relationship of
the two vessels, with the aorta lying in an anterior and rightward position relative to the pulmonary artery (28,38) (Fig. 5.34). The pulmonary and systemic circulations are in parallel rather than in series, and survival depends on some type of communication at the atrial, ventricular, or great artery level.

The first definitive repair for D-TGA was the atrial-switch operation (the Mustard or Senning operation) (39). The atrial septum was excised, and a baffle was constructed within the atria to direct systemic venous blood across the mitral valve into the left ventricle and pulmonary venous blood across the tricuspid valve into the right ventricle (Fig. 5.35). Complications of the atrial-switch operation include leakage or obstruction of the baffle and caval or pulmonary stenosis at the reconnection sites (40). The atrial-switch operation has been replaced
by the arterial-switch operation, in which the pulmonary artery and ascending aorta are transected above the semilunar valves and then switched, so that the aorta and coronary arteries are connected to the left ventricle and the pulmonary artery is connected to the right ventricle (Fig. 5.36) (41,42,43).

In double-outlet right ventricle, >50% of the aorta and pulmonary artery arise from the right ventricle (Fig. 5.38). The aorta is positioned anterior and to the right of the pulmonary artery (28). A VSD is always present, and pulmonic stenosis is frequently present. Double-outlet left
ventricle is a rare anomaly in which both arteries originate from the morphologic left ventricle.

In double-inlet ventricle, >50% of both atria are connected to one dominant ventricle. The communication can be via two separate atrioventricular valves or through a common atrioventricular valve. Double-inlet ventricle has also been referred to as single ventricle, but this is somewhat of a misnomer, since in most instances, a rudimentary second ventricle is present. The dominant ventricle can be either the left (most common) (Fig. 5.39) or the right. Associated cardiac lesions include pulmonary stenosis or atresia, subaortic stenosis, and coarctation.

Truncus arteriosus is the result of failure of truncoconal septation. In this malformation, a single arterial trunk with a single valve arises from the heart to supply the pulmonary, systemic, and coronary arteries. The truncus straddles a high membranous VSD. The single semilunar valve or truncal valve is malformed with the number of cusps varying from two to six, resulting in truncal valvular stenosis or insufficiency. A right arch is present in about 25% of cases (44).

The pulmonary arteries can arise as a single short vessel from the posterior aspect of the truncus (type I, most common form) (Fig. 5.40) or they can have separate origins from the posterior aspect of the truncus (type II) (Fig. 5.41), sides of the truncus (type III), or the descending aorta (type IV) (44,45). Treatment is surgical division of the common trunk and reimplantation of the right and
left pulmonary arteries to the main pulmonary artery (Fig. 5.42).

In hemitruncus, one of the two pulmonary arteries arises from the ascending aorta and the other arises from the main pulmonary artery (Fig. 5.43). Anomalous origin of the right pulmonary artery is more common than anomalous origin of the left pulmonary artery.

In total anomalous pulmonary venous connection (TAPVC), the pulmonary veins have no connection with the left atrium and drain directly into a systemic vein or the right heart (46). The anomaly is classified into four types based on site of connection: (a) supracardiac to the left brachiocephalic vein, right superior vena cava, or azygous vein; (b) cardiac to the coronary sinus or the right atrium; (c) infracardiac to the portal vein, hepatic veins, or inferior vena cava; and (d) mixed. Common associated defects include atrial septal defect and patent foramen ovale. Pulmonary overcirculation is present except in the infracardiac type, where the drainage is obstructed, resulting in pulmonary edema.

Surgery is anastomosis of the common pulmonary venous channel to the back of the left atrium. The postoperative anaotomy of the reimplanted veins, including the complication of stenosis at the site of reimplantion, can be easily shown by CT (Fig. 5.44).

Patients with Eisenmenger physiology have large left-to-right shunts that cause pulmonary vascular disease and pulmonary hypertension, with consequent reversal of the direction of shunting. The chronic exposure of the pulmonary vessels to increased blow flow leads to vascular obstructive disease (47). As the pulmonary vascular resistance increases and exceeds systemic resistance, right ventricular pressure increases and the shunt is reversed. As right-to-left shunting develops, cyanosis appears. CT findings include (a) enlarged central and main pulmonary arteries, which may be calcified; (b) small peripheral vessels; and (c) right heart enlargement (Fig. 5.45). Treatment for severe Eisenmenger physiology is either lung transplantation with repair of the cardiac defect or combined heart–lung transplantation.

Although either coronary artery can arise from the pulmonary artery, the left coronary artery is more often abnormal. Affected patients present in infancy with symptoms of heart failure. Immediately after birth there is physiologic pulmonary hypertension, so that blood flows from the pulmonary artery into the anomalous coronary artery. As pulmonary vascular pressure drops, antegrade flow through the left coronary artery diminishes and the right coronary artery provides retrograde flow to the left coronary artery via collateral vessels. Rather than perfusing the ventricular myocardium, blood in the left coronary artery flows into the lower-resistance pulmonary artery, leading to myocardial ischemia, infarction, and failure. CT findings include aberrant origin of the left coronary artery from the pulmonary artery and collateral circulation between the right and left coronary arteries (Fig. 5.46). Treatment is surgical reimplantation of the anomalous coronary artery into the aorta or creation of a conduit from the left coronary ostia to the aorta.

Anomalous origin and course of the coronary arteries can be benign or life threatening and associated with sudden death during exercise. In the pediatric population, these anomalies are most commonly associated with congenital heart diseases, such as transposition of the great arteries, single ventricle, and tetralogy of Fallot, but they can be isolated findings.

The four identifiable patterns of anomalous origin of the coronary arteries are (a) right coronary artery arising from the left coronary sinus, (b) left coronary artery arising from the right coronary sinus, (c) left circumflex and left anterior descending arteries arising from the right coronary sinus, and (d) left or right coronary artery arising from the noncoronary sinus. A coronary artery arising from the opposite coronary sinus can have four courses, based on its relationship to the aorta and pulmonary artery (a) between the aorta and pulmonary artery (interarterial), (b) posterior to the aorta (retroarotic), (c) anterior to the pulmonary artery (prepulmonic), or (d) beneath the right ventricular outflow tract (subpulmonic) (Fig. 5.47). The interarterial course is associated with a high risk for sudden cardiac death; the other courses appear to be benign (50) (Fig. 5.48).

With non-ECG-gated cardiac CT, the sensitivity of visualizing the origin of the proximal coronary arteries is about 82% in children and adolescents (51). Although data are not available in large series of children, studies in adults using ECG-gated-multislice CT have shown that the sensitivity for detecting the coronary arteries exceeds 90% (52).

Coronary artery aneurysms in children are usually a complication of Kawasaki disease. Kawasaki disease, also known as mucocutaneous lymph node syndrome, is an acute vasculitis of unknown cause involving small and
medium-sized arteries (53,54,55). Clinical findings include fever, rash, conjunctivitis, stomatitis, erythema, which is often most intense on the hands and feet, and cervical adenopathy. Coronary artery aneurysms tend to arise in the proximal parts of the coronary arteries; they may be fusiform, saccular, or cylindrical, and they may calcify (Fig. 5.49). Other sites for aneurysm formation include the iliac, femoral, and axillary arteries.

Causes of pericardial effusions in children include heart failure, cardiac surgery, viral pericarditis, collagen vascular
diseases, metastatic disease, and renal insufficiency. On CT, pericardial effusion appears as a layer of fluid, partially or totally surrounding the heart. Simple effusions or transudates have near-water attenuation. Hemorrhagic or more proteinaceous fluid (exudates, malignant effusions) have attenuation greater than that of water. Small effusions accumulate posterior to the left ventricle and left atrium. Larger effusions extend ventral and lateral to the right ventricle and atrium and cephalad to the origin of the great vessels (Fig. 5.50). Associated findings, such as tamponade, pericardial thickening, and tumor, also may be detected by CT. CT findings of tamponade are flattening of the right ventricle and atrium and dilatation of the inferior vena cava. Recognition of tamponade is important as it can lead to rapid hemodynamic compromise.

The causes of pericarditis include infectious, inflammatory, or idiopathic causes; radiation therapy; cardiac surgery; and cardiac trauma. CT findings of acute and chronic pericarditis include pericardial thickening and effusion. Chronic pericardial inflammation can lead to constrictive pericarditis, which is characterized by reduced ventricular filling. The CT features of constrictive pericarditis are a tubular or conical ventricular shape, thickened pericardium, and pericardial effusion; secondary sequelae include dilated atria, hepatic veins, and inferior vena cava (Fig. 5.51). Pericardial calcification is a late finding.

Pericardial cysts may be congenital or acquired. Most cysts are asymptomatic and detected incidentally on chest radiography or echocardiography. Acquired cysts are usually encapsulated or loculated pericardial effusions caused by infection, pericarditis, trauma, or cardiac surgery. Congenital cysts are formed when a portion of the pericardium is pinched off during early development (56). They commonly have thin smooth walls, occur along the right cardiophrenic angle, and do not communicate with the pericardial cavity. On CT, simple pericardial cysts filled with serous fluid have the same attenuation as water and do not enhance after administration of intravenous contrast agents (Fig. 5.52). Cysts containing highly proteinaceous fluid or blood may have greater attenuation on CT and may contain debris or septations.

Pericardial tumors are much more likely to be metastatic than primary (56,57). Sources of pericardial metastases in children are leukemia, lymphoma, neuroblastoma, hepatoblastoma, Wilms tumor, and Ewing sarcoma. CT findings of metastases are irregularly thickened pericardium or a pericardial mass and effusion. Primary pericardial tumors are usually benign and include pericardial cyst (Fig. 5.52), teratoma, lipoma, fibroma, angioma, and lymphangioma. Lipomas typically have fat attenuation on CT. Teratomas usually contain calcium or fat as well as some low-attenuation fluid. Fibromas are soft tissue masses, whereas angiomas are vascular masses. Lymphangiomas appear as septated fluid attenuation lesions. Malignant tumors include lymphoma and sarcoma; they appear as soft tissue masses. Malignant neoplasms can be associated with high-attenuation serosanguineous pericardial effusion.

Polysplenia syndrome is associated with acyanotic heart lesions (commonly VSD, double-outlet right ventricle,
anomalous pulmonary venous connection), azygous return of the inferior vena cava, left isomerism, normal or horizontal liver, and polysplenia (Fig. 5.56). Malrotation is also common.

The asplenia syndrome is associated with cyanotic heart diseases (commonly artrioventricular canal, single ventricle, pulmonic stenosis or atresia, D-TGA), right-sided isomerism, horizontal liver, small midline stomach, and absence of the spleen.