Editors: Siegel, Marilyn J.
Title: Pediatric Body CT, 2nd Edition
> Table of Contents > Chapter 4 - Great Vessels
Chapter 4
Great Vessels
The advent of multidetector CT angiography has revolutionized vascular imaging. Faster scanning times, increased anatomic coverage, and high-quality reconstructions owing to the use of thin collimation have enabled CT to become a reliable, widely used tool for the diagnostic evaluation of intrathoracic and abdominal vascular pathology (1,2,3,4,5,6).
Abnormalities of the intrathoracic vessels, including the aorta and its branches, the superior vena cava, and the pulmonary arteries and veins, vary widely in their anatomic spectrum and clinical presentation depending on the site of involvement, type of lesion, and presence or absence of compression of adjacent structures. In many patients, vascular anomalies or pathology may alter the appearance of the mediastinum and be detected on plain radiographs, prompting a CT study. In these circumstances, CT can serve as a relatively noninvasive method for definitive diagnosis. In other cases, an anomaly or abnormality may be detected incidentally on CT scans performed for another indication. In a similar fashion, congenital and acquired abnormalities of the abdominal aorta and inferior vena cava can be identified on sonography, prompting CT, or detected as incidental findings.
Accurate diagnosis of vascular abnormalities depends on an understanding of normal anatomy as well as knowledge of the spectrum of anatomic variants that can occur and mimic pathology. In this chapter, the thoracic vascular structures are discussed, followed by a discussion of the abdominal vessels. For each of these two areas, there are three subsections. First, a brief review of normal vascular anatomy is presented. Second, commonly encountered congenital anomalies are discussed. The third subsection describes noncongenital or acquired pathology of the mediastinal and abdominal vessels.
Technique
CT of the great vessels is performed with a pulmonary embolism protocol using the following parameters: collimation 0.6 to 1.5, pitch 1 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 22-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 not routinely performed for evaluation of the mediastinal great vessels, with the exception of some pulmonary vein studies. Retrospective ECG gating is used for CT angiographic evaluation of the site of insertion of the pulmonary veins into the left atrium and pulmonary vein stenosis. The volumetric data are reconstructed at 3 to 5/mm for routine viewing and at 2 mm for multiplanar reformatting and 3D reconstructions. A standard algorithm is used for reconstruction.
Normal Thoracic Vascular Anatomy
Thoracic Aorta
The thoracic aorta can be divided into five segments: aortic root, ascending aorta, proximal aortic arch, posterior aortic arch, and descending thoracic aorta (Fig. 4.1). The aortic root is the short segment that arises from the base of the heart; it includes the aortic valve, annulus, and sinus of Valsalva. The ascending aorta begins at the aortic root and ends at the right innominate artery. The aortic arch begins at the right innominate artery and extends to the ligamentum arteriosum. This is divided into two segments: the proximal arch extending between the right innominate artery and the origin of the left subclavian artery, and the posterior arch or isthmus extending from the left subclavian artery to the ligamentum arteriosum.
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The descending thoracic aorta begins at the level of the ligamentum arteriosum and extends to the aortic hiatus in the diaphragm.
Figure 4.1. Thoracic aorta and branches, normal anatomy. Sagittal reformation shows the five aortic segments: aortic root (ARo), ascending aorta (AA), aortic arch (Ar), aortic isthmus (Is), and descending aorta (DA).
The normal branching pattern of the aortic arch is the right innominate artery, which in turn bifurcates into the right common carotid and right subclavian arteries, the left carotid artery, and then the left subclavian artery (Fig. 4.2). The ductus arteriosus or ligamentum arteriosum arises distal to the origin of the left subclavian artery. Two common variations of the normal branching pattern are, first, a common brachiocephalic trunk, in which the right innominate and left carotid arteries arise as a single vessel from the arch; and second, separate origin of the left vertebral artery from the aortic arch proximal to the origin of the left subclavian artery rather than from the subclavian artery (7). The frequency of each variant is approximately 10% (7).
Pulmonary Arteries
The main pulmonary artery lies within the pericardium. It divides into the right and left pulmonary arteries behind and to the left of the ascending aorta (Fig. 4.3). The right pulmonary artery is longer and larger than the left. It passes posterior to the ascending aorta, superior vena cava, and right upper lobe pulmonary vein and anterior to the right main bronchus where it divides into two branches. The upper branch supplies the right upper lobe, and the lower branch supplies the middle and lower lobes of the right lung. The left pulmonary artery is shorter and slightly smaller than the left. It courses anterior to the descending aorta and the left main bronchus where it divides into two branches to supply the upper and lower lobes of the left lung.
Figure 4.2. Arch vessel anatomy. The order of arterial branching from the aortic arch is right innominate artery (IA), which bifurcates into the right subclavian (RS) and right carotid (RC) arteries, left carotid (LC) artery and left subclavian (LS) artery. (See color insert.)
Pulmonary Veins
There are typically four pulmonary veins—single right and left superior and inferior pulmonary veins (Fig. 4.4). The right superior pulmonary vein receives blood from the right upper and middle lobes. The left superior vein receives blood from the left upper lobe, including the lingula. The right and left inferior veins receive blood from the corresponding lower lobes.
Two common anatomic variations are conjoined veins and accessory veins (Fig. 4.5). A conjoined vein occurs when superior and inferior veins open into the left atrium via a common ostium. Conjoined veins are more common on the left side (Fig. 4.5A). Accessory or supernumerary pulmonary veins are extra veins with independent junctions with the left atrium separate from the superior and
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inferior pulmonary veins. They occur more frequently on the right side, with separate drainage of the right middle lobe or superior segment of the right lower lobe occurring most often (Fig. 4.5B).
Figure 4.3. Pulmonary arteries, normal anatomy. A: Axial CT scan. After arising from the main pulmonary artery (M), the right pulmonary artery (R) extends posteriorly and to the right, coursing behind the ascending aorta (A) and superior vena cava (S). The left pulmonary artery (L) extends posteriorly and to the left of the main pulmonary artery, coursing anterior to the descending aorta (D). B: 3D volume-rendered CT scan showing the main pulmonary artery (MPA), right (RPA) and left (LPA) pulmonary arteries, and branch arteries. (See color insert.)
Figure 4.4. Pulmonary veins, anatomy. A: Normal anatomy. 3D reconstruction (posterior view) shows the four pulmonary veins draining into the left atrium. Right superior (RS), right inferior (RI), left superior (LS), left inferior (LI) pulmonary veins.
Superior Vena Cava and Azygos Venous System
The superior vena cava is formed by the left and right innominate veins (also referred to as the brachiocephalic veins), which receive blood from the extremities and the head and neck.
The azygos vein penetrates the diaphragm via a small opening and ascends in the right paravertebral area. At the level of the T5-6 vertebrae, it curves to the right and then passes anterior to the right main-stem bronchus to drain into the posterior aspect of the superior vena cava. The curved part of the azygos vein that enters the superior vena cava is termed the azygos arch. The hemiazygos vein penetrates the diaphragm through the aortic hiatus, ascends on the left, and then at about the T8 level crosses the midline, coursing anterior to the vertebra and posterior to the aorta to drain into the azygos vein (Fig. 4.6).
Thoracic Vascular Anomalies
Aortic Anomalies
Anomalies of the aorta and its branch vessels are found in 0.5% to 3% of the population (8,9). Aortic anomalies can be classified into five groups: left aortic arch, right aortic arch, double aortic arch, cervical arch, and innominate artery.
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Figure 4.5. Pulmonary veins, anatomic variations. A: Conjoined vein. Coronal 3D reconstruction shows common ostia of the left pulmonary veins (arrow) where they enter the left atrium (LA). B: Accessory vein. Coronal 3D reconstruction shows separate drainage of the right middle lobe vein (arrow) into the left atrium.
Left Arch with Aberrant Right Subclavian Artery
The left aortic arch with an aberrant right subclavian artery is the most common congenital abnormality of the aortic arch vessels and occurs in about 0.5% to 2% of the population (8,9,10). It is nearly always asymptomatic, except in the rare cases where there is a vascular ring produced by a right ductus arteriosus or ligamentum arteriosum arising from the descending aorta and extending to the ipsilateral pulmonary artery. In these cases, patients may present with dysphagia or stridor. Treatment in symptomatic patients is surgical division of the ductus or ligamentum.
Figure 4.6. Azygos system. Posterior coronal reformation shows the hemiazygos vein (arrow) crossing the midline to enter the azygos vein (A) which enters the superior vena cava (S).
The anomalous right subclavian artery is seen on CT as the last of the major arteries to arise from the aortic arch, and so the order of branching is right common carotid, left common carotid, left subclavian, and right subclavian arteries. The aberrant artery originates from the proximal descending aorta and crosses the mediastinum from left to right, passing behind the esophagus to reach the right arm (Fig. 4.7). It may be dilated at its site of origin
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(so-called diverticulum of Kommerell), and the underlying esophagus may be compressed. In this circumstance, patients may complain of dysphagia.
Figure 4.7. Left aortic arch with aberrant right subclavian artery. Axial CT image shows a left aortic arch (A) and an aberrant right subclavian artery (arrow) coursing posterior to the esophagus (e) and trachea. Note also a left superior vena cava (S).
Right Aortic Arch Anomalies
A right aortic arch occurs in approximately 0.05% to 0.2% of the population (8,9). Although there are at least five potential right arch anomalies, only two are relatively common: the right arch with aberrant left subclavian artery and the right arch with mirror-image branching (10).
In the right arch anomaly with an aberrant left subclavian artery, which is rarely associated with congenital heart disease, the aberrant artery arises from the arch as its last branch. The order of arterial branching is as follows: left common carotid artery, right common carotid artery, right subclavian artery, and left subclavian artery. The left subclavian artery courses cephalad from right to left and passes behind the esophagus to reach the left arm (Fig. 4.8). Like its counterpart on the right side, the vessel can dilate at its origin. Patients are symptomatic when the trachea and esophagus are compressed by the surrounding mediastinal vessels (Fig. 4.8C). In symptomatic patients, treatment is surgical division of the ductus or ligamentum.
Figure 4.8. Right aortic arch with aberrant left subclavian artery. A: Axial CT scan demonstrates a right aortic arch (A) with the aberrant left subclavian artery (arrow) crossing the mediastinum posteriorly. B: Coronal 3D reconstruction (posterior view). The left subclavian artery (arrow) is the last vessel arising from the aorta. LCA, left common carotid artery; RCA, right carotid artery; right subclavian artery (arrowhead). C: Coronal 3D airway reconstruction shows focal compression of the trachea (arrow) by the anomalous subclavian artery. (See color insert.)
A mirror-image right arch is almost always associated with congenital heart disease, especially with tetralogy of Fallot. In this anomaly, the great arteries arise in the
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following order: left innominate artery (giving rise to the left subclavian and carotid arteries), right carotid artery, and right subclavian artery (Fig. 4.9). Because there is no vascular ring, stridor and dysphagia are absent. Treatment may be needed for the associated congenital heart disease but not for the mirror image arch per se.
Figure 4.9. Right arch, mirror-imaging branching. A: Axial image shows a right aortic arch (A) without a crossing vessel. B: 3D volume-rendered reconstruction (posterior view) shows the right arch and origins of the arch vessels: left innominate (IA) giving rise to the left subclavian (LS) and left carotid (LC), right carotid (RC), and right subclavian (RS) arteries. (See color insert.)
Figure 4.10. Double aortic arch. Axial (A) and coronal (B) maximal-intensity projections demonstrate patent right (R) and left (L) arches encircling the trachea. The high-attenuation structure within the trachea is an endotracheal tube.
Double Aortic Arch
Double arch occurs in 0.05% to 3% of the population (8,9). This anomaly is characterized by the presence of two aortic arches arising from a single ascending aorta (Fig. 4.10). Each arch gives rises to its own subclavian and carotid arteries, and then they reunite to form a single descending
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aorta. The descending aorta may be on the left (more common) or right side. Typically, the right arch is larger and more cephalad than the left arch. Both limbs of the aorta may be patent and functioning, or one limb may be atretic or hypoplastic, usually the left one (Fig. 4.11) (11). Treatment is surgical division of the smaller arch (Fig. 4.12). Following surgery, some patients may have persistent airway obstruction related to tracheomalacia
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as a result of long-standing extrinsic airway compression (12).
Figure 4.11. Double aortic arch: Axial CT scan (A) and 3D volume-rendered image (B) show a dominant right arch (A) and area of atresia (arrow) in the smaller left arch. (See color insert.)
Figure 4.12. Double arch. A: Preoperative posterior 3D reconstruction shows patent right (R) and left (L) arches. B: Postoperative posterior 3D reconstruction following ligation of the left arch. (Reprinted with permission from
Chan MSM, Chu WCW, Cheung KL, et al. Angiography and dynamic airway evaluation with MDCT in the diagnosis of double aortic arch associated with tracheomalacia. AJR Am J Roentgenol 2005;185:1248–1251.
) (See color insert.)
Figure 4.13. Cervical arch. A: Coronal multiplanar reformation shows a right-sided aortic arch (A) ascending to the level of the thoracic inlet, the so-called cervical arch. B: Axial scan showing the aorta (A) crossing the mediastinum posterior to the trachea and esophagus to descend on the left.
Cervical Aortic Arch
Cervical aortic arch is a rare anomaly characterized by a high-riding ascending aorta, which extends above the level of the clavicles before making a sharp downward turn to descend through the thorax (Fig. 4.13). A right-sided cervical arch is more common than a left-sided cervical arch (13). Associated anomalies include absence of the innominate artery, origin of the contralateral subclavian artery from the descending proximal aorta, and a retroesophageal course of the descending aorta with the aorta descending on the side contralateral to the arch. Most patients are asymptomatic; rarely, patients present with dysphagia from esophageal compression by the retroesophageal aorta. Stridor may be a presenting finding if there is a vascular ring, produced by a ductus arteriosus or ligamentum arteriosum arising from the upper descending aorta and extending to the ipsilateral pulmonary artery.
Innominate Artery Compression of the Trachea
Innominate artery compression of the trachea is an abnormality in which there is anterior compression of the trachea by the innominate artery. The site of compression is usually at or just below the thoracic inlet (Fig. 4.14). Affected patients can present with stridor, cough, and dyspnea (14). The treatment for severely symptomatic patients is surgical suspension of the innominate artery from the sternum. Following surgery, some patients may remain symptomatic because of associated tracheomalacia.
Pulmonary Artery Anomalies
Absence or Proximal Interruption of the Pulmonary Artery
In this anomaly, the right or left pulmonary artery is interrupted proximally, usually within 1 cm of its origin from the main pulmonary artery (9,15,16). The pulmonary arteries distally are diminutive and supplied by systemic collateral vessels. Interruption of the left pulmonary artery is commonly associated with other anomalies, including right aortic arch, septal defects, patent ductus arteriosus, and tetralogy of Fallot. Right pulmonary artery interruption is usually an isolated finding. Most patients come to clinical attention in the first year of life, presenting with dyspnea or recurrent pulmonary infections. In older patients, the anomaly can be detected incidentally on CT scans obtained for other reasons.
CT findings include abrupt termination of the proximal pulmonary artery, collateral vessel formation, and a small or absent ipsilateral lung (Fig. 4.15). Collateral pathways include aortopulmonary anastomoses from
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the thoracic aorta, direct origin of a pulmonary artery from the aorta, and coronary to left pulmonary artery anastomoses.
Figure 4.14. Innominate artery compression. A: Tracheal compression by the right innominate artery (arrow) is seen just below the level of the thoracic inlet. B: Sagittal multiplanar reformation of the airway demonstrates anterior compression of the trachea (arrow).
Pulmonary Artery Sling
In pulmonary sling, the left pulmonary artery arises from the posterior part of the right pulmonary artery, passes lateral to the trachea above the right main bronchus, and then crosses the mediastinum between the trachea and esophagus to reach the left hilum. Respiratory distress is a common presentation in infants and young children. Airway obstruction may be related to tracheobronchial compression by the crossing vessel, tracheomalacia, or complete cartilaginous rings, the latter causing long-segment tracheal narrowing and a horizontal course of the main bronchi (i.e., T-shaped carina) (17,18,19,20) (Figs. 4.16 and 4.17). Treatment is surgical division of the anomalous pulmonary artery and reanastomosis to the main pulmonary artery (21). Tracheoplasty may also be required in patients with complete cartilaginous rings.
Figure 4.15. Interrupted main pulmonary artery. Axial CT image shows the right (R) and main (M) pulmonary artery crossing over to the left hemithorax and herniation of the right lung across the midline anteriorly. The left lung and left pulmonary artery are absent.
Pulmonary Venous Anomalies
Partial Anomalous Pulmonary Venous Drainage
In this condition, one or more pulmonary veins have an anomalous connection, producing shunting of oxygenated blood into the right heart circulation. This can be an isolated anomaly or it can be associated with other anomalies of the lung or cardiovascular system. In children, right-sided anomalous connection is twice as common as left-sided anomalous connection (22,23). The CT diagnosis of anomalous return is based on recognition of the abnormal course of an intraparenchymal pulmonary vein (24,25,26,27). This is especially well seen on 3D reconstructions (28).
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Figure 4.16. Pulmonary artery sling. Axial CT (A) and 3D volume rendering (B) demonstrate the left pulmonary artery (L) arising from the proximal right pulmonary artery (R) before crossing behind the trachea to reach the left lung. C: Coronal 3D reconstruction of the airway shows minimal compression of the right tracheal wall (arrow) just above the carina. (See color insert.)
Figure 4.17. Pulmonary sling with cartilaginous rings. 3D CT lumenogram demonstrates long-segment tracheal narrowing (arrows) and a T-shaped carina. (Case courtesy of Joseph Schoepf, M.D.)
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Figure 4.18. Anomalous venous return from the right upper lobe. Axial CT scan (A) and coronal 3D volume-rendered image (B) show the anomalous right superior pulmonary vein (arrow) emptying into the superior vena cava (S). (See color insert.)
An anomalous right superior pulmonary vein usually drains to the superior vena cava, although it may join with the azygous vein, azygous arch, or right atrium (Figs. 4.18 and 4.19). This type of venous anomaly can be associated with a sinus venosus atrial septal defect. An anomalous left superior pulmonary vein drains into the left brachiocephalic vein (Fig. 4.20). It courses laterally to the aortic arch and aorticopulmonary window.
Figure 4.19. Anomalous venous return from the right upper and right lower lobes. Posterior coronal 3D volume-rendered image shows the anomalous right superior (open arrow) and right inferior (white arrow) pulmonary veins emptying into the superior vena cava (S). (See color insert.)
An anomalous right lower lobe vein can drain into the subdiaphragmatic inferior vena cava, portal or hepatic vein, or azygos vein (Fig. 4.21). This can be an isolated finding or it can be associated with hypoplasia of the right lung and pulmonary artery (Fig. 4.21) (referred to as the scimitar, venolobar, or hypogenetic lung syndrome) (22,25,26,29). Other associated anomalies include systemic arterial blood supply to the hypogenetic lung, extralobar sequestration, and horseshoe lung (30).
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Figure 4.20. Anomalous left upper lobe pulmonary venous return, young adult. A: Axial CT image demonstrates an enlarged vein (arrow) lying lateral to the aortic arch (A). B: Coronal 3D reconstruction shows the anomalous connection between the left superior pulmonary vein (arrow) and brachiocephalic vein (BC). (See color insert.)
Stenosis of the Pulmonary Veins
In stenosis of an individual pulmonary vein, one or more pulmonary veins have a localized stenosis at the junction with the left atrium (Fig. 4.22). This may be an isolated finding or it may be associated with cardiac anomalies. The cause is thought to be abnormal incorporation of the vein into the left atrium (31).
Figure 4.21. Anomalous right lower lobe venous return. A: Axial CT scan shows an anomalous vessel (arrow) in the right lower lobe, a small right lung, and rightward mediastinal shift in this patient with scimitar syndrome. B: 3D volume-rendered image (posterior view) shows the anomalous right inferior pulmonary vein (arrow) draining into the inferior vena cava (arrowhead). (See color insert.)
Pulmonary Varix
Pulmonary varix can be congenital or the result of chronic pulmonary hypertension. On CT, the varix enhances concurrently with the pulmonary veins, and there is continuity between the varix and the adjacent pulmonary veins or the left atrium (see Chapter 3, Fig. 3.27).
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Figure 4.22. Pulmonary vein stenosis. Posterior 3D volume-rendered image shows stenosis of the left inferior pulmonary vein (arrow). The patient had undergone a prior ablation for atrial fibrillation. (See color insert.)
Left Superior Vena Cava
A persistent left superior vena cava occurs in 1% to 3% of the general population (32). It can be an isolated finding, but more often it is found in patients with congenital heart disease. The left vena cava lies anterior to the left subclavian artery and lateral to the left common carotid artery. It descends lateral to the aortic arch, anterior to the left hilum and lateral to the main pulmonary artery, and empties into a dilated coronary sinus (Fig. 4.23) (33). On rare occasions, it drains into the left atrium, which results in a right-to-left shunt. In most patients, a right-sided superior vena cava is also present and is usually smaller than the left superior vena cava. The superior vena cava and coronary sinus enhance intensely if contrast agent is injected into the left arm. This anomaly needs to be differentiated from anomalous venous return from the left upper lobe (see above) and the normal superior intercostal vein (see following).
The left superior intercostal vein drains the left second to fourth intercostal veins. It courses along the superolateral border of the aortic arch and then empties into the left brachiocephalic vein (Fig. 4.24). Inferiorly it connects with the accessory hemiazygos vein. The left superior intercostal vein produces the “aortic nipple” shadow on frontal chest radiographs.
Thoracic Vessels: Noncongenital Pathology
Aortic Aneurysm
An aneurysm is a permanent dilatation of the aortic wall. Age-related normal standards for the ascending and descending thoracic aorta in children have been established and can be used for reference when aortic enlargement is suspected (34).
Aneurysms Associated with Connective Tissue Disorders
The two inherited fibrillopathies that can affect the aorta and its branches are Marfan syndrome and Ehlers–Danlos syndrome (35,36,37). These diseases result from molecular defects in the fibrillin gene, which is responsible for the structural integrity of vascular smooth muscle. In Marfan syndrome, the abnormality in the fibrillin gene is located on chromosome 15q21 (35,36). Changes of cystic medial degeneration also can be seen in these syndromes. On CT, there is typically fusiform dilatation of the ascending aorta, which decreases in size as it approaches the arch (Fig. 4.25). Dilatation of the sinuses of Valsalva and the aortic root or aortic annulus, termed annuloaortic ectasia, also can be seen with Marfan syndrome.
Aneurysms Associated with Aortitis
Noninfective aortitis, such as Takayasu disease, may be a cause of an aortic aneurysm. Takayasu arteritis is a large vessel vasculitis that results in chronic inflammation of the arterial wall. Although wall damage can lead to aneurysm formation, it more often results in stenoses and vascular occlusion (see below).
Infected Aneurysms
Infected aortic aneurysm, also known as mycotic aneurysm, is an endarteritis that is usually of bacterial origin. It
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most often is secondary to hematogenous dissemination, but it may occur via local spread of adjacent infection. Factors predisposing to mycotic aneurysm include indwelling umbilical artery catheters, bacterial endocarditis, and intravenous drug use. Mycotic aneurysms are typically saccular and involve the descending aorta and thoracoabdominal junction above the level of the renal arteries (Fig. 4.26). Periaortic soft tissue stranding and fluid may also be noted.
Figure 4.23. Left superior vena cava. A: Axial CT scan shows a left superior vena cava (arrow) lateral to the aortic arch (A). B: At a lower level, the cava (arrow) courses anterior to the left hilum. C: At the base of the heart, the left-sided cava empties into the coronary sinus (arrow). D: Coronal multiplanar reformation shows the longitudinal course of the left superior vena cava (S). Note also a right superior vena cava (white arrow) and anomalous insertion of the hepatic veins (black arrows) into the right atrium.
Figure 4.24. Left superior intercostal vein. The superior intercostal vein (arrow) is seen coursing lateral to the aortic arch.
Figure 4.25. Marfan disease with associated aortic aneurysm. Coronal reformatted CT shows fusiform dilatation of the ascending aorta (AA).
Figure 4.26. Mycotic aneurysm. Axial CT scan (A) and sagittal 3D reconstruction (B) show a saccular aneurysm (arrow) of the descending aorta in a 5-year-old girl who had an umbilical artery catheter as a neonate. (Case courtesy of Jose Domingo Arce, Santiago, Chile.)
Posttraumatic Aneurysms
Posttraumatic aneurysms can be a sequela of blunt trauma or a complication of cardiac surgery. They are false (pseudo) aneurysms contained by adventitia. Posttraumatic aneurysms usually arise near the aortic isthmus (38) (Fig. 4.27). Postsurgical aneurysms usually occur at the cannulation site for cardiopulmonary bypass. Both types of aneurysms are typically saccular, may calcify, and may enlarge over time.
Aortic Dissection
Aortic dissection is rare in children. Factors predisposing to dissection include weakness of the media associated with coarctation, inherited connective tissue disorders (e.g., Marfan and Ehlers–Danlos syndromes), and Takayasu disease. Typically patients present with acute onset of chest or back pain. Dissections almost always occur in the ascending aorta (type A Stanford classification). Descending aortic dissections (type B) can occur in Marfan syndrome and are almost always an extension of an ascending aortic dissection.
Figure 4.27. Posttraumatic aneursym. Sagittal multiplanar reformation shows saccular dilatation (arrow) of the aorta near the isthmus.
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Figure 4.28. Aortic dissection as a complication of Marfan syndrome, 20-year-old woman. A, B: Two axial CT sections through the lower mediastinum show an intimal flap (arrow) in the descending aorta separating inner true (T) and outer false (F) lumina. C: Sagittal multiplanar reformation shows the full extent of the dissection, which begins in the mid descending aorta and extends to the level of the celiac axis.
The classic CT finding of acute aortic dissection is two contrast-filled channels—a true and a false lumen—separated by an intimal flap (39,40). The true lumen can be recognized by its intense early enhancement, continuity with the lumen of the nondissected aorta, sometimes smaller diameter, and its location on the inner curvature of the aorta. The false lumen is typically located on the outer curvature of the aorta (Fig. 4.28). It may contain cobwebs, which represent strands of media tissue, and thrombus, and it may have attenuation lower than that of the true lumen reflecting slower flow. Absence of contrast enhancement of the false channel suggests that it is thrombosed.
Aortic Stenosis or Occlusive Disease
The most common causes of aortic occlusion are Takayasu arteritis and midaortic dysplastic syndrome.
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Figure 4.29. Takayasu arteritis, 4-year-old girl with hypertension. A, B: Two axial CT scans show luminal narrowing of the thoracic and abdominal aorta with associated thickening of the aortic walls (arrows). The descending thoracic aorta narrowed to a maximal diameter of 3.5 mm and the abdominal aorta to a diameter of 2 mm. C: Sagittal multiplanar reformation show diffuse, irregular narrowing of the thoracic and abdominal aorta. In addition, there is involvement of the left common carotid artery (white arrow). Note also multiple posterior collateral vessels (black arrows).
Takayasu arteritis is a large vessel vasculitis that affects the aorta and its major branches as well as the pulmonary artery (41). Clinical findings include absent pulses, hypertension, angina, claudication, syncope, and visual impairment. CT findings in the early phase of the disease are abnormal wall thickening and enhancement. During the late or occlusive phase of the disease, findings include stenosis, occlusion, wall thickening, mural calcification, intraluminal thrombus, and less often aneurysmal dilatation (41,42,43,44) (Fig. 4.29). Collateral vessel formation may also be noted. The stenoses are usually long segment. Aortic involvement may be limited to the arch or it may involve the descending aorta or both the thoracic and abdominal aorta.
Midaortic syndrome is thought to be congenital and due to a noninflammatory aortitis, leading to hypoplasia. It usually manifests in the second decade of life, presenting as hypertension, abdominal pain, and/or weakness or absence of the femoral pulses (45,46). Commonly, the stenosis is limited to the thoracoabdominal junction, but it may extend into the descending abdominal aorta, and it may involve the visceral branches of the aorta, such as the
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superior mesenteric and renal arteries (Fig. 4.30). Treatment of midaortic syndrome is surgical revascularization with prosthetic or autologous venous grafts (Fig. 4.31). This syndrome can be distinguished from Takayasu arteritis by absence of arterial wall thickening, which is present in Takayasu arteritis but not in the midaortic syndrome.
Figure 4.30. Midaortic syndrome. Coronal (A) and sagittal (B) multiplanar reformations show stenosis of the thoracoabdominal aorta (arrows). The area of stenosis includes the ostium of the superior mesenteric artery (arrowhead).
Idiopathic Arterial Calcification
Idiopathic arterial calcification of infancy is a rare and usually fatal disease of unknown cause (47). Histologically, it is characterized by calcification within the internal elastic laminae, intimal proliferation and fibrosis, and luminal narrowing. Calcifications can occur in systemic, pulmonary, and coronary arteries. Most patients present in early infancy with cardiac failure and respiratory distress. Death is usually in the first year of life from myocardial ischemia owing to coronary artery involvement, although longer survival has been described (47). The calcium–phosphate profile is usually normal.
Superior Vena Cava Obstruction
The causes of superior vena cava obstruction include intrinsic lesions, usually catheter-induced intraluminal thrombus; malignant neoplasms, such as lymphoma; and fibrosing mediastinitis. The characteristic CT finding of superior vena caval obstruction is absent enhancement of the caval lumen, which may be associated with extrinsic compression or encasement by neoplasm or inflammatory tissue. Collateral venous channels also may be noted (Fig. 4.32). Collateral pathways include the azygos/hemiazygos, internal mammary, lateral thoracic, paravertebral, superficial thoracoabdominal, and epigastric veins.
Normal Abdominal Vascular Anatomy
The inferior vena cava (IVC) arises from the confluence of the two common iliac veins at the level of the fifth lumbar
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vertebra. It then ascends to the right of the aorta to enter the chest and eventually the right atrium. On transverse CT, the IVC appears as a thin-walled tubular structure with a round or flat shape and a size that varies among individuals as well as in the same individual at different levels. Performance of a Valsalva maneuver usually results in a more distended IVC. A small, flat IVC at multiple levels may be a sign of hypovolemic shock. The blood within the lumen of the cava has an attenuation similar to that of the abdominal aorta.
Figure 4.31. Midaortic syndrome. A: Coronal volume-rendered image shows long-segment stenosis (arrows) of the abdominal aorta. B: Posterior coronal image following surgery shows the left-sided aortic bypass (arrowheads) and the native aortic stenosis (arrows). (See color insert.) (Case courtesy of Edward Lee, MD, Boston, MA.)
Figure 4.32. Superior vena caval obstruction. CT scan demonstrates a small superior vena cava (arrow), multiple mediastinal collateral vessels, and an enlarged azygos vein (arrowhead). The cause of the obstruction was fibrosing mediastinitis.
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Figure 4.33. Congenital venous anomalies. Diagram shows relationship of inferior vena cava (IVC), aorta (Ao), and left renal vein (LRV) in various anomalies. AZV, azygos vein; SVC, superior vena cava; T,. (Reprinted from
Warshauer DM, Lee JKT, Patel H. Retroperitoneum. In: Lee KTL, Sagel SS, Stanley RJ, et al. Computed Body Tomography with MRI Correlation. Philadelphia: Lippincott Williams & Wilkins; 2006:1155–1232, with permission.
)
Abdominal Vascular Anomalies
Developmental anomalies of the venous system (Fig. 4.33) are usually discovered as incidental findings on CT performed for other clinical indications. Their recognition is essential so that they are not misinterpreted for lymphadenopathy. Careful scrutiny of serial scans and the administration of intravenous contrast medium will help to clarify the vascular nature of these structures (48,49,50,51).
Azygos Continuation of the Inferior Vena Cava
In this anomaly, also referred to as interrupted inferior vena cava, the suprarenal segment of the vena cava fails to develop and blood returns to the heart through the azygous and hemiazygous systems. This anomaly may be isolated or associated with other anomalies, including situs abnormalities and polysplenia.
On CT, a normal IVC extends from the union of the common iliac veins to the level of the renal veins. On more cephalic scans, the inferior vena cava is absent. In its place, there is an enlarged azygos vein and often an enlarged hemiazygos vein (Fig. 4.34). The azygos and hemiazygos veins course cephalad in the retrocrural area to join with the superior vena cava. The hepatic veins drain directly into the right atrium.
Transposition of the Inferior Vena Cava (Left IVC)
This condition is characterized by a single, right-sided IVC above the level of the renal veins, a vascular channel crossing either anterior or posterior to the aorta connecting the renal veins, and a single left-sided IVC below the level of the renal veins (Fig. 4.35).
Duplication of the Inferior Vena Cava
This anomaly is characterized by a single, right-sided IVC, smaller than usual, above the level of the renal
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veins and two cavae below the level of the renal veins. Proximally, the left cava joins with the left renal vein; distally, the left cava ends at the level of the common iliac veins. The right and left cavae join via a vascular channel that courses either anterior or posterior to the aorta at the level of the renal veins.
Figure 4.34. Azygous continuation of inferior vena cava. A: Contrast-enhanced CT demonstrates a dilated azygos vein arch (arrowheads) draining into the superior vena cava (S). B: A more caudal scan shows the dilated azygous vein (V) lateral to the descending aorta (A). Note the absence of the intrahepatic inferior vena cava.
Figure 4.35. Left inferior vena cava. A: Contrast-enhanced CT shows a right-sided IVC. B: At a lower level, the IVC crosses to the left. C: More inferiorly, the IVC is positioned to the left of the aorta. Black arrow, IVC. Perihepatic fluid is related to a ventriculoperitoneal shunt. White arrow, shunt catheter.
Figure 4.36. Inferior vena caval thrombus. Axial CT (A) and coronal reformation (B) scans. A large hypoattenuating thrombus (white arrows) from a Wilms tumor (T) distends the intrahepatic part of the inferior vena cava. Note also hepatic metastases (M), omental metastases (black arrows), and pelvic lymphadenopathy.
Retrocaval (Circumcaval) Ureter
Retrocaval ureter almost invariably occurs on the right. In this anomaly, the right ureter passes posterior to the IVC and then around its medial aspect, usually at the L3 vertebral level, to partially encircle the IVC.
Abdominal Vessels: Noncongenital Pathology
Caval Thrombosis and Tumor Extension
Inferior vena caval thrombosis in children is most often associated with malignancies, usually Wilms tumor and hepatic neoplasms. Other causes include a deficiency of protein C or protein S (52), an indwelling venous catheter, vascular stasis, nephrotic syndrome, and extension of renal vein thrombosis or adrenal hemorrhage.
CT diagnosis of venous thrombosis is based on demonstration of an intraluminal filling defect, often associated with luminal enlargement and wall enhancement (Fig 4.36). In partial occlusion, the intraluminal thrombus is surrounded by contrast-enhanced blood. In chronic occlusion, the IVC may atrophy and calcify and dilated collateral vessels, such as the azygos and hemiazygos veins, may be seen (Fig. 4.37). Enhancement of the thrombus following the intravenous administration of contrast medium suggests tumoral rather than bland (hemorrhagic) thrombus.
Caution must be taken not to mistake a pseudothrombus artifact caused by laminar flow with a true thrombus. Flow artifacts are caused by the mixing of densely opacified renal venous blood and less densely opacified
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infrarenal caval blood; they are usually seen above the level of the renal veins. Pseudothrombus can be differentiated from a true thrombus by its ill-defined borders and by the use of delayed scans.
Figure 4.37. Calcified thrombus. Coronal multiplanar reformation shows a calcified thrombus in the inferior vena cava (arrow) in this patient with a history of an indwelling umbilical venous catheter as an infant. Note also dilated azygos (A) and hemiazygos (H) veins.
Abdominal Aortic Stenosis
Abdominal aortic stenosis may be the result of Takayasu arteritis (Fig. 4.29) or midaortic dysplastic syndrome (Figs. 4.30 and 4.31).
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