Coarctation of the aorta is the 6th most common type of congenital heart disease, accounting for approximately 7 % of all congenital heart anomalies in children with a male–female ratio of 2:1 (Tanous et al. 2009; Restrepo et al. 2012; Murillo et al. 2012). Coarctation of the aorta is defined as a hemodynamically significant, focal, shelf-like narrowing of the descending aorta typically distal to the takeoff of the left subclavian artery in the region of the ligamentum arteriosum. The shelf of the coarctation is most often juxtaductal, but it may be pre- or postductal (Backer and Mavroudis 2000; Tanous et al. 2009; Murillo et al. 2012). Coarctation of the aorta may be a feature of Turner’s syndrome and is associated with a bicuspid aortic valve in more than 70 % of patients (Tanous et al. 2009; Murillo et al. 2012). Other intracardiac abnormalities may also be found in association with coarctation, especially in patients who present in infancy and are more likely to have associated left ventricular outflow obstruction and/or associated ventricular septal defects, which may be perimembranous, muscular or misalignment. Mitral valve abnormalities resulting in mitral stenosis, such as a supravalvular mitral ring, dysplastic mitral valve leaflets, or a parachute mitral valve may also be present in patients with coarctation. Subaortic stenosis is also a potentially associated lesion. When this group of left-sided obstructive lesions occurs together, they are referred to as the Shone complex (Moene et al. 1987; Rosenquist 1974; Shone et al. 1963; Moulaert et al. 1976).

Unless corrected in infancy, collateral circulation gradually develops between the proximal aorta and the distal aorta to bypass the coarctation. The vessels contributing to the collateral circulation may become markedly enlarged and tortuous by early adulthood (Hellinger et al. 2011; Restrepo et al. 2012).

The age of presentation and symptoms depends on the severity, rather than on the site, of the coarctation, the presence or absence of associated lesions and, most importantly, the patency of the ductus arteriosus, as the ductus acts as a bypass for blood distal to the coarctation. Once the ductus closes, in cases of high-grade stenosis, congestive heart failure symptoms develop. The blood pressure is elevated in the vessels originating proximal to the coarctation; the blood pressure as well as the pulse pressure below the coarctation are typically lower (Epelman and MacDonald 2010; Jenkins and Ward 1999). Coarctation of the aorta recognized after infancy is rarely associated with significant symptoms. Older children are frequently referred to a cardiologist when they are found to be hypertensive on routine physical examination. Arterial pulses in the legs are either absent or weak and delayed, and there is hypertension in the arm, or blood pressure readings in the arm are higher than those in the leg. In normal children, the systolic pressures in the thigh or calf are higher by 5–10 mm Hg than that in the arm.

If aortic coarctation is left untreated, it is expected that 90 % of the patients will die before the age of 50 (Campbell 1970). The most common causes of death are congestive heart failure, aortic rupture, bacterial endocarditis, and intracranial hemorrhage (Campbell 1970).

On chest radiography, the findings will vary according to the severity of the coarctation and the presence of the associated pathology. Abnormality in the contour of the isthmus region is the most important sign in coarctation, and it may be the only finding. The contour of the proximal descending aorta may resemble a number 3 (“Figure of 3 sign”); the upper portion of the 3 is related to the combined shadows of the pre-stenotic aortic knob and the dilated proximal portion of the left subclavian artery; the waist of the “figure of 3” represents the coarctation itself; and the lower portion corresponds to the poststenotic dilatation of the descending aorta (Epelman and MacDonald 2010). Rib notching between the fourth and eighth ribs may be observed in older children but rarely before the age of seven. Rib notching is the result of pressure erosion caused by dilated or tortuous intercostal arteries, which serve as collaterals between the internal mammary arteries and the descending aorta. The first, second, and third ribs do not typically exhibit rib notching, as the intercostal arteries at these level originate from the thyrocervical trunk, which originates above the coarctation (Epelman and MacDonald 2010).

Critical preoperative information to be evaluated with cross-sectional imaging (Figs. 10 and 11) includes (1) the anatomy of the transverse aorta and the aortic isthmus, including the orthogonal dimensions and the relationship to other arch vessels; (2) the presence and extent of any pre-coarctation hypoplasia; (3) the severity of the obstruction and hemodynamics, including quantification of collateral flow, flow velocity, flow volume, and pressure gradients across the stenosis, by phase contrast MR imaging; (4) the presence of previously mentioned associated intracardiac anomalies, such as bicuspid aortic valve and mitral valve abnormalities (Konen et al. 2004); and (5) the presence of aneurysm, particularly in cases after prior surgical or endovascular interventions (Weinberg and Whitehead 2010; Restrepo et al. 2012; Konen et al. 2004; Hom et al. 2008).

While surgery is the mainstay of treatment in infants, endovascular repair with balloon angioplasty and stenting is being increasingly used, particularly in older children (Holzer et al. 2010). Commonly used surgical procedures include resection and end-to-end anastomosis, subclavian flap aortoplasty, synthetic patch repair, and aortic bypass interposition grafting or bypass grafting (Jenkins and Ward 1999). The continued monitoring of patients with stents is required to assess for complications such as aneurysm formation or the need for reintervention (Holzer et al. 2010).

Tubular hypoplasia of the aortic arch may involve one or all segments and characteristically presents in association with other intracardiac anomalies, ranging in severity from a bicuspid aortic valve to a more complex left-sided obstructive lesion or hypoplastic left heart syndrome (Brown et al. 2009). A common rule of thumb for determining aortic arch hypoplasia in neonates on echocardiography is an internal luminal diameter of less 1 mm/kg (Brown et al. 2009). This finding may coexist with associated discrete, focal coarctation in nearly 30 % of the cases (Brown et al. 2009). The narrowing is smooth and usually affects the isthmus, although in rare occasions, it may affect the entire arch (Brown et al. 2009; Matsui et al. 2007). Recognition of this instance is important, as it may affect the operative approach, and in some complex patients, the surgeon may opt for a median sternotomy instead of the classic left thoracotomy (Brown et al. 2009) (Fig. 12).

Interruption of the aortic arch (IAA) is an uncommon, hemodynamically critical, obstructive aortic arch anomaly. In this condition, the left and right fourth embryonic arches have regressed and there is lack of luminal continuity between the ascending and descending aorta. It accounts for 1.5 % of all congenital heart disease. In IAA, the flow between the ascending and descending aorta and the lower body is maintained only by a ductal arch (patent ductus arteriosus) or collateral circulation once the ductus closes (Kellenberger 2010; Hellinger et al. 2011; Weinberg and Whitehead 2010; Weinberg et al. 1998; Mishra 2009). The affected neonates are typically not cyanotic and normal appearing at birth, but they present usually later on, characteristically during the first 2 weeks of life, with congestive heart failure that worsens as the ductus closes (Hellinger et al. 2011; Kellenberger 2010).

The classification system proposed by Celoria and Patton (Celoria and Patton 1959) is the most widely accepted and classifies these anomalies in three types according to the point of interruption: (1) in type A, the interruption occurs distal to the left subclavian artery origin at the aortic isthmus; (2) in type B, the interruption takes place between the origins of the left common carotid artery and the left subclavian artery (Fig. 13); and (3) in type C, the interruption takes place proximal to the left common carotid artery, between the origins of the innominate and left common carotid arteries (Weinberg and Whitehead 2010; Kellenberger 2010; Hellinger et al. 2011). Type B is the most common type, and it accounts for approximately two-thirds of the cases. Type C is the least common type, occurring in less than 2 % of the cases (Collins-Nakai et al. 1976; Norwood et al. 1983; Vouhe et al. 1990; Jonas et al. 1994; Serraf et al. 1996; Tlaskal et al. 1998; Brown et al. 2006; Flint et al. 2010; Hellinger et al. 2011). Similar to other arch anomalies involving the fourth embryonic arch, Type B interruption is commonly observed in patients with DiGeorge syndrome (Goldmuntz et al. 1998; Momma 2010). In addition, IAA rarely occurs in isolation and a patent ductus arteriosus is always present. VSD, as well as a left ventricular outflow tract obstruction, are commonly present. Less commonly, IAA may be associated with aorto-pulmonary window, truncus arteriosus, and double outlet right ventricle (Mishra 2009; Restrepo et al. 2012). These patients are surgically treated early in life; if left untreated, death may ensue at a median age of 4–10 days (Kellenberger 2010; Mishra 2009). Imaging should be tailored to identify the precise type of IAA, to measure the distance between the segments, to assess the dimensions of the left ventricular outflow tract, and to describe the morphological characteristics of the patent ductus arteriosus and any associated anomalies.

Patent ductus arteriosus (PDA) is the most common heart defect in neonates, and it is defined as incomplete closure of the ductus arteriosus beyond functional closure after birth. Its incidence is quite high in premature infants, being as high as 60 % in those born before 28 weeks of gestation (Corno and Festa 2009b). PDA consists of a vascular connection usually between the left proximal pulmonary artery and the descending thoracic aorta (Fig. 14), just distal and opposite to the left subclavian artery ostium bypassing the deflated lungs. However, the precise point of connections can vary substantially (Backer and Mavroudis 2000; Berko and Haramati 2012; Kondrachuk et al. 2012). Rarely, the PDA can insert onto the right pulmonary artery. The PDA usually connects to the left pulmonary artery, even in the presence of a right aortic arch. Bilateral patent ducti have also been rarely described (Corno and Festa 2009b). The ductus arteriosus usually closes within 72 h of birth, but if it does not, it is considered unlikely that it will close spontaneously (Berko and Haramati 2012). It typically closes beginning from the pulmonary end, leaving a diverticulum on the aortic side, which eventually closes as well (Corno and Festa 2009b). This anomaly usually persists in patients with underlying congenital heart disease, commonly ASD or VSD, but it is also seen in diseases that are ductus-dependent, such as hypoplastic left heart syndrome, aortic arch interruption, and pulmonary atresia with or without an intact ventricular septum (Corno and Festa 2009b). On cross-sectional imaging, the ductus arteriosus appears as a tubular structure joining the aorta and the proximal left pulmonary artery (Fig. 14), which can be easily missed if only axial imaging is used (Kondrachuk et al. 2012). Conversely, the location, caliber, and morphology of the PDA can be easily depicted with multiplanar reconstructions in isolated defects or in complex cardiac malformations. PDA in older patients may be potentially complicated by aneurysm formation, calcification, and rupture. An increased risk for bacterial endarteritis has also been reported (Moore and Brook 2012; Berko and Haramati 2012). Premature infants are given a trial of prostaglandin inhibitors. If this fails, surgical ligation is performed via a left posterolateral thoracotomy. Percutaneous coil occlusion is reserved for older children (Kondrachuk et al. 2012; Corno and Festa 2009b).

Major aortopulmonary (systemic to pulmonary) collateral arteries (MAPCAs) characteristically develop in the setting of severe pulmonary stenosis/atresia or right ventricular outflow tract obstruction serving as the primary source of blood flow to the lungs (Kondrachuk et al. 2012; Flamm 2010). MAPCAs are highly variable in their presence, size, and origin. They may originate more frequently from the descending aorta or, less frequently, from the arch vessels, or the subclavian, internal mammary or intercostal arteries (Lofland 2004; Kondrachuk et al. 2012). MAPCAs may be diminutive or extremely large, resulting in over-circulation to the portion of the lung supplied by them. They may exhibit focal areas of stenosis either at their origin or anywhere along their course. MAPCAs may also have connections with the native pulmonary arteries (Lofland 2004, 2009). Multidetector CT or contrast-enhanced MRI with 3D reconstructions are extremely helpful for their full depiction and mapping prior to unifocalization or interventional embolization (Fig. 15) (Corno and Festa 2009c; Lofland 2004, 2009).