In patients with TOF with pulmonary atresia, precise preoperative delineation of the presence, size and confluency of the pulmonary arteries, and major aortopulmonary collateral arteries (MAPCAs) is necessary for surgical planning. This diagnostic task can be readily accomplished with cardiac MDCT (Goo et al. 2005a; Greil et al. 2006) (Fig. 4). As a result, the procedure time of catheter angiography and possibility of overlooked MAPCAs can be substantially reduced. Nonetheless, conventional catheter angiography is necessary for identifying communications between pulmonary arterial feeders. Abnormalities of the branch pulmonary arteries that are well depicted on MDCT include an abnormal origin or course such as in truncus arteriosus or pulmonary artery sling (Fig. 5). The branch pulmonary arteries can be atretic, stenotic, or hypoplastic related to decreased blood flow during growth (Fig. 6), extrinsic compression, or as a result of a surgically altered course or anastomosis such as a palliative shunt between the systemic and pulmonary artery circulation (Fig. 7).

Pulmonary embolism (PE) is an uncommonly diagnosed condition in children. The clinical presentation is often subtle because symptoms are nonspecific and can be masked by the underlying clinical condition. Delays in diagnosis are frequent because definite signs of associated pulmonary or cardiac dysfunction appear to be less common in children than in adults. Specific risk factors for PE in the pediatric patient include associated deep venous thrombosis, indwelling central venous catheters, cardiac surgery, thrombotic disorders, vascular malformations, and malignancy and multiple factors are often present in the same patient (Babyn et al. 2005). PE may complicate CHD particularly after surgical treatments, such as cavopulmonary connections (Fig. 8). Diagnostic strategies for detection and treatment of PE in children are mostly extrapolated from evidence that has been compiled in the adult literature.

CT has become the first choice of imaging modalities for detection of PE in symptomatic patients. MDCT has led to improved visualization of peripheral pulmonary arteries for detection of small emboli (Lee et al. 2011), and conventional pulmonary angiography is now rarely performed. Once regarded as the best first noninvasive study for the diagnostic work-up of PE, nuclear medicine perfusion scintigraphy is also now infrequently requested because as many as 73 % of studies are interpreted as indeterminate (PIOPED 1990) and have poor interobserver correlation (Blachere et al. 2000), and there is limited ability to make alternative diagnoses. Despite excellent diagnostic accuracy of MDCT in detecting PE, thromboembolic risk factors should be used as a first-line triage tool to guide more appropriate use of CT pulmonary angiography in children, with associated reductions in radiation exposure and costs (Lee et al. 2012).

MDCT angiography findings of acute pulmonary embolism include intraluminal filling defects in the main and branch pulmonary arteries that can partially or completely fill the lumen (Fig. 9). When the embolus completely fills the lumen of a branch pulmonary artery, the artery can enlarge relative to similar-sized arteries in the hilum. Lung parenchymal findings with PE include peripheral wedge-shaped opacities, hyperlucency, and mosaic perfusion. Findings of acute right ventricular failure, such as right ventricular enlargement and septal flattening, may be present in severe cases.

A classic finding of chronic PE is an intraluminal filling defect that makes an obtuse angle with the vessel wall and creates an appearance of asymmetric wall thickening (Fig. 10). Contrast-enhanced peripheral arteries can have irregular wall thickening related to recanalization and the residual thrombus may be calcified. Enlarged bronchiolar and systemic collateral arteries can also be seen in association with chronic PE.

Recently, dual-energy CT scanning enables us to evaluate PE and lung perfusion defects at the same time (Fig. 11). In addition to the accurate diagnosis of PE, pulmonary blood volume assessment using dual-energy CT can predict right heart strain and clinical outcome (Bauer et al. 2011). This emerging CT imaging technique for evaluating PE may also be useful in pediatric patients (Goo 2010b; Zhang et al. 2012).

MDCT angiography is quite useful and accurate in evaluating anomalous pulmonary venous connections when echocardiography is limited in fully identifying types and obstructions of these total or partial anomalous pulmonary venous connections (Kim et al. 2000). When associated with CHD, pulmonary vein stenosis (PVS) is most often extrinsic due to compression by other vascular structures, or associated with the site of a prior surgical anastomosis (Fig. 12). PVS can rarely be intrinsic and rapidly progressive and refractory to all forms of treatments (Latson and Prieto 2007; Devaney et al. 2006). Progressive PVS can occur in children with or without CHD and MDCT can assess PVS noninvasively and accurately (Ou et al. 2009).

Congenital pulmonary venolobar syndrome or scimitar syndrome is a heterogeneous group of congenital anomalies of the thorax that may occur singly or in combination. The main components of the congenital pulmonary venolobar syndrome are hypogenetic lung (lobar agenesis, aplasia, or hypoplasia), partial anomalous pulmonary venous return, absence of a pulmonary artery, pulmonary sequestration, systemic arterialization of the lung, absence of the inferior vena cava (IVC), and accessory diaphragm (Konen et al. 2003). Horseshoe lung may be rarely associated with this syndrome (Goo et al. 2002). MDCT provides a complete evaluation of all pulmonary and systemic vascular, tracheobronchial and pulmonary parenchymal anomalies, necessary in patients under consideration for surgical repair (Fig. 13).

Coarctation of the aorta is a congenital obstructive aortic arch anomaly presenting with arch hypoplasia and focal narrowing of the aortic isthmus at the junction of the ductus arteriosus and the aorta. MDCT can demonstrate anatomic features of the anomaly and collateral arteries, if present (Fig. 14), that are helpful for optimal surgical planning. It should be noted that the anomaly is a dynamic process showing progressive obstruction in young infants when the patent ductus arteriosus (PDA) is present. Following surgical repair of coarctation, MDCT can be used to detect residual stenosis, recoarctation, or aneurysm formation at the repair site. In order to avoid radiation exposure in children, MRI may be favored for long-term follow-up after surgical repair. MDCT is the imaging method of choice for evaluating associated airway abnormalities and in-stent stenosis after stent placement. In addition, MDCT is also useful for assessing early post-procedural complications, such as pseudoaneurysm formation and dissection (Fig. 15).

Interrupted aortic arch (IAA) is a rare aortic anomaly defined as a complete luminal and anatomic discontinuity of the aortic arch. The anomaly is classified as three types depending on the site of interruption, i.e., distal to the subclavian artery in type A, between the second carotid and ipsilateral subclavian arteries in type B, and between two carotid arteries in type C. Type B is most common in the Western population (Fig. 16), while type A is most common in the Asian population (Lee et al. 2006). Each type may be further divided into three subtypes depending on the origin of the subclavian artery, i.e., normal in subtype 1, aberrant in subtype 2, and isolated in subtype 3. In addition to the anatomic types of IAA, cardiac CT may be used to evaluate the distance between the proximal and distal segments of IAA, the sizes of a PDA, the aorta and the thymus, the presence of subaortic stenosis, and other cardiac defects (Yang et al. 2008). In IAA, a right aortic arch is almost always associated with DiGeorge syndrome and/or chromosome 22q11 deletion (McElhinney et al. 1999b). As in coarctation of the aorta, IAA may be associated with the bicuspid aortic valve and other components of Shone complex including supravalvular mitral membrane, parachute mitral valve, and subaortic stenosis.

Valvular aortic stenosis occurs in approximately 3–6 % of patients with CHD and is often associated with a congenital bicuspid aortic valve. Although the effective valve area can be reduced at birth, the stenosis of a bicuspid valve is progressive and clinical symptoms do not usually develop until young adulthood. MDCT is seldom used for evaluating valvular aortic stenosis because anatomic details of the aortic valve in children are not well-seen on CT and high radiation dose is necessary for the complete assessment of the aortic valve. The surgical approach to aortic valve replacement for severe congenital aortic stenosis in young patients is difficult because placement of a mechanical valve is not a good option because of the risk of long-term anticoagulation. Other options include placement of homograft or xenograft valves. In the Ross procedure, the stenotic aortic valve is replaced with the patient’s pulmonary valve, and a right ventricle to pulmonary artery conduit is placed.

Supravalvular aortic stenosis (SVAS) may be non-syndromic or associated with Williams syndrome. ECG-synchronized cardiac CT can show not only SVAS, but also the bicuspid aortic valve, dilated coronary arteries, coronary ostial stenosis, and left ventricular hypertrophy (Liu et al. 2007). SVAS may be focal (the “hourglass” appearance) (Fig. 17) or diffuse (10–30 % of cases), starting at the sino-tubular junction. Aortoplasty is indicated in symptomatic patients or in those with a transaortic valve gradient greater than or equal to 50 mmHg (Scott et al. 2009).

Marfan syndrome and type IV Ehlers-Danlos syndrome are connective tissue disorders that can have cardiovascular manifestations. Both are associated with cystic medial necrosis of the aortic wall, which adversely affects the ability of the aortic wall to withstand systemic pressures, leading to dilatation. The characteristic findings of the aorta include dilatation of the aortic root and proximal ascending aorta and effacement of the sino-tubular junction. The dilatation of the aortic root results in suboptimal coaptation of the aortic valve cusps, which can lead to aortic regurgitation that can further weaken the aortic wall as more throughput volume is needed to maintain cardiac output. Both echocardiography and MRI can be used for serial follow-up of ascending aorta size and aortic regurgitation in patients with Marfan syndrome. CT may be used in some patients with severe chest wall deformity limiting echocardiographic evaluation or who cannot tolerate lengthy MRI evaluation (Ha et al. 2007). In general, when the maximum diameter of the ascending aorta is 1.5 times that of the descending thoracic aorta at the level of the diaphragm, an aneurysm is considered to be present. In addition to the maximal diameter of the aortic root, its growth rate should be considered in determining the optimal timing for surgical replacement of the aortic root and/or ascending aorta. Serious complications of Marfan’s or type IV Ehlers-Danlos syndrome include dissection and rupture of the ascending aorta (Fig. 18). Although transesophageal echocardiography (TEE) or MRI could be performed urgently if dissection is suspected, MDCT angiography with multiplanar reconstruction is a highly sensitive and specific technique for the detection and characterization of the extent and orientation of the intimal flap, delineation of the true and false lumens, presence of intramural hematoma, and involvement of the major aortic branches and coronary arteries (McMahon and Squirrell 2010).