Vascular Malformations of the Pediatric Chest M.J. Siegel

Aortic Anomalies

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 0.5-2% of the pop- ulation [1, 2] (Fig. 1). The right subclavian artery is the last of the major arteries to arise from the aortic arch; thus, the order of branching is right common carotid, left com- mon carotid, left subclavian, and right subclavian. A di- verticulum-like outpouching, referred to as a Kommerell diverticulum, may be seen at the site of origin of the aber- rant vessel. Patients are usually asymptomatic, since this lesion does not represent a true vascular-ring anomaly.

Double Aortic Arch

The term ‘vascular ring’ refers to encirclement of the tra- chea and esophagus by vascular and/or ligamentous

structures. These anomalies of the aorta and its branch vessels are found in 0.5-3% of the population [1, 2]. The two common vascular rings are the double aortic arch and the right arch with an aberrant left subclavian artery.

A double arch occurs in 0.05-3% of the population.

Double aortic arch is characterized by the presence of two aortic arches arising from a single ascending aorta. Each arch usually gives rises to a subclavian and carotid artery, before reuniting to form a single descending aorta, which is usually left-sided. As a result, the great vessels have a symmetric appearance in the superior mediastinum. Both limbs of the aorta are usually patent and functioning, with the right limb being larger and more cephalad than the left (Fig. 2). Occasionally, one limb, usually the left, contains an atretic segment [3]. The descending aorta may be on the left (more common) or right side. The double arch is generally an isolated anomaly and associated heart disease is rare. Patients are symptomatic because the two compo- nents of the arch encircle the trachea and esophagus.

IDKD 2007

Vascular Malformations of the Pediatric Chest

M.J. Siegel

Washington University School of Medicine, Mallinckrodt Institute of Radiology, St. Louis, MO, USA

Fig. 2. Double aortic arch in a 6-month-old boy. Axial maximal in- tensity projection demonstrates right (R) and left (L) arches encir- cling the trachea. The high attenuation structure within the trachea is an endotracheal tube

Fig. 1.Left aortic arch with aberrant right subclavian artery in an adolescent male. Axial CT image shows a left aortic arch (A) and an aberrant right subclavian artery (arrow) coursing posterior to the trachea and esophagus

Right Aortic Arch Right Aortic Arch Anomalies

A right aortic arch occurs in approximately 0.05-0.2% of the population [1, 2]. There are two main types of right arch: one with an aberrant left subclavian artery and the other with mirror-image branching.

Right Aortic Arch with Aberrant Left Subclavian Artery

In this anomaly, the aortic arch is right-sided and the great arteries arise from the arch in the following order: left common carotid artery, right common carotid artery, right subclavian artery, and left subclavian artery. The left sub- clavian artery courses cephalad from right to left and pass- es behind the esophagus to reach the left arm (Fig. 3). An

aortic diverticulum may be present at the point of origin of the left subclavian artery. The descending aorta is right- sided. Patients may be symptomatic because the mediasti- nal vessels encircle the trachea and esophagus. This anomaly is rarely associated with congenital heart disease.

Right Aortic Arch with Mirror-Image Branching

In this anomaly, the aortic arch passes to the right of the trachea and esophagus and over the right main-stem bronchus (Fig. 4). The great arteries originate from the arch in the following order: left innominate artery, right carotid artery, and right subclavian artery. Since this is not a true vascular ring, symptoms of airway or esophageal compression are absent. A mirror-image right arch is al- most always associated with congenital heart disease.

Cervical Aortic Arch (High-Riding Aortic Arch)

A cervical aortic arch is characterized by a high-riding elongated aortic arch, which extends cephalad in the me- diastinum anterior to the brachiocephalic vein, usually to the level of the subclavian arteries; it may extend above the level of the clavicles into the cervical soft tissues (Fig. 5).

Associated anomalies include absence of the innominate artery, origin of the contralateral subclavian artery from the descending proximal aorta, and a retro-esophageal course of the descending aorta with the aorta descending on the right side contralateral to the arch. A right-sided cervical arch is more common than a left-sided one [4].

Most patients are asymptomatic and the diagnosis is an in- cidental finding on imaging examinations.

Innominate Artery Compression

The innominate artery arises from the left aortic arch and crosses anterior and to the right of the trachea. As it crosses the mediastinum, it can compress the trachea

year-old girl. Axial CT scan demonstrates a right aortic arch (A) with the aberrant left subclavian artery (arrow) crossing the medi- astinum posteriorly

Fig. 4a, b. Right arch, mirror-image branching in a young adult. a, b Axial images show a right aortic arch (A) without a crossing vessel.

The pulmonary artery (PA) is dilated following a patch-graft procedure for repair of pulmonic stenosis associated with tetralogy of Fallot

a b

anteriorly, resulting in stridor, cough, and dyspnea [5].

At CT, anterior compression of the trachea by the in- nominate artery is seen at or just below the level of the thoracic inlet (Fig. 6). Tracheomalacia is an associated anomaly.

Aortic Coarctation

Two major types of coarctation are recognized: pre-duc- tal (also known as the infantile form) and post-ductal (adult form) [6]. In the pre-ductal form of coarctation, narrowing of the aorta occurs immediately above the lev- el of the origins of the left subclavian artery and the lig- amentum arteriosum. This form of coarctation is associ- ated with long segment narrowing of the aortic arch and other congenital heart disease. Collateral vessel forma- tion is usually absent. Affected patients usually present in the first six months of life with heart failure.

In the post-ductal form, the coarctation is almost always located at the junction of the distal aortic arch and the de- scending aorta, immediately below the obliterated ductus arteriosus. The ascending aorta is usually dilated while the descending aorta just below the coarctation shows post- stenotic dilatation (Fig. 7) [7]. Collateral circulation be- tween the proximal and distal parts of the aorta is estab- lished via large intercostal and internal thoracic arteries.

Patients are usually asymptomatic and the condition is rec- ognized during evaluation of hypertension or a coexistent cardiac anomaly, usually a bicuspid aortic valve.

Pulmonary Arteries

Absence or Proximal Interruption

Proximal interruption or the absence of a main pulmonary artery is characterized by interruption of the right or left pulmonary artery, usually within 1 cm of its origin from the main pulmonary artery [8] (Fig. 8). The peripheral pul- monary arteries distally are diminutive and supplied by sys- temic collateral vessels. Collateral pathways include aor- topulmonary anastomoses from the thoracic aorta, direct origin of a pulmonary artery from the aorta, and coronary

vical arch in a 5- year-old boy. Axial (a) and sagittal (b) multiplanar refor- matted CT scans show a right-sided aortic arch (A) as- cending to the level of the thoracic inlet a

b

Fig. 6. Innominate artery compression in a 5-year-old boy. Tracheal compression by the right innominate artery (arrow) is seen just be- low the level of the thoracic inlet

Fig. 7.Aortic coarctation, post-ductal type, in a 4- year-old boy. Sagittal multiplanar reformation demonstrates high-grade focal constriction (arrow) of the aortic lumen just below the origin of the left subclavian artery (S).

The posterior intercostal and internal mammary arteries are enlarged

to left pulmonary artery anastomoses. The affected lung is hypoplastic. 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. Interruption of the right pulmonary artery is usually an isolated finding. Patients may be asymp- tomatic and the diagnosis made as an incidental detection on imaging studies obtained for other clinical indications.

Pulmonary Sling

In pulmonary sling, the left pulmonary artery arises from the right pulmonary artery, passes above the right main bronchus, and then crosses between the trachea and esophagus to reach the left hilum [9] (Fig. 9). In most

cases, the anomalous artery compresses the right main- stem bronchus. The pulmonary sling usually comes to clinical attention in infants because of the compressive effect of the artery on the airway and/or associated tra- cheal or bronchial stenosis due to cartilaginous rings [9- 11]. Cartilaginous rings cause long segment tracheal nar- rowing and a horizontal course of the main bronchi (i.e., T-shaped carina). The malformation may be asympto- matic in older individuals.

Patent Ductus Arteriosus

The ductus arteriosus represents persistence of part of the sixth aortic arch. Except for neonates, most pa- tients with patent ductus arteriosus are asymptomatic and the lesion is usually diagnosed by the discovery of a murmur. The CT finding is that of a small tubular structure connecting the descending proximal aorta with the distal main or proximal left pulmonary artery (Fig. 10).

Pulmonary Veins

Partial Anomalous Venous Connection

In a partial anomalous venous connection, the pulmonary veins from one or more lobes have an anomalous con- nection, producing shunting of oxygenated blood into the right-heart circulation. The condition can be an isolated anomaly or associated with other anomalies of the lung or cardiovascular system [12, 13].

Partial Anomalous Drainage of the Left Upper Lung

The left upper lobe pulmonary vein usually empties into the left brachiocephalic or innominate vein. CT shows a

right (R) and main (M) pulmonary artery crossing over to the left hemithorax and herniation of the right lung across the midline an- teriorly. The left lung and left pulmonary artery are absent

Fig. 9. Pulmonary artery sling in a 5-month-old girl. Axial CT demonstrates the left pulmonary artery (L) arising from the proxi- mal right pulmonary artery (R), before crossing behind the trachea to reach the left lung

Fig. 10.Patent ductus arteriosus in an adolescent boy. Axial CT im- age demonstrates an enhancing tubular structure (arrow) arising from the descending aorta (A)

vertical vein coursing lateral to the aortic arch and aor- topulmonary window. A normal left superior pulmonary vein is not identified in the left hilum; instead, a small lingular vein will be seen anterior to the left main bronchus (Fig. 11). Blood flow is caudocranial. Partial anomalous venous return needs to be distinguished from a persistent left superior vena cava [14]. Two vessels will be seen in the left hilum in the latter anomaly (the left ca- va and left pulmonary vein), whereas only one will be found in this location in anomalous venous return. In ad- dition, the persistent left superior vena cava drains into the coronary sinus.

Partial Anomalous Drainage of the Right Upper Lobe

The right upper lobe drains into the superior vena cava, usually near the caval-right-atrial junction. A communi- cation located posterosuperior to the oval fossa, termed a sinus venosus defect, is a common associated finding [15, 16]. Less often, anomalous drainage from the right lung is into the right atrium or azygos vein or to the azy- gos arch.

Abnormal Drainage of the Right Lower Lobe

The anomalous pulmonary vein from the right lower lobe usually drains to the inferior vena cava, although it may join with the suprahepatic part of the inferior vena cava, hepatic vein, portal vein, azygos vein, coronary sinus, or right atrium [17, 18] (Fig. 12). The scimitar or hypoge- netic lung syndrome is a special form of anomalous pul- monary venous return from the right lung that is associ- ated with a hypoplastic right lung and pulmonary artery, and mediastinal shift. Other associated anomalies include systemic arterial blood supply from the thoracic or ab- dominal aorta to the hypogenetic lung and horseshoe lung. The latter is a rare anomaly in which the poster- obasal segments of both lungs are fused behind the peri- cardial sac [19].

Pulmonary Varix

Varicosity of the pulmonary vein can be congenital or the result of chronic pulmonary hypertension. Patients may be asymptomatic or present with hemoptysis. 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 (Fig. 13).

Fig. 11a, b. Anomalous left upper lobe pulmonary venous return in a young adult. a Axial CT image demonstrates an enlarged vein (arrow) lying lateral to the aortic arch. b Coronal 3D reconstruc- tion shows the anomalous connection between the left superior pul- monary lobe vein (arrows) and brachiocephalic vein (V)

a

b

Fig. 12. Anomalous venous return from the right lower lobe.

Coronal maximal intensity projection shows the anomalous pul- monary veins (arrow) emptying into the inferior vena cava

Systemic Venous Anomalies Persistent Left Superior Vena Cava

Left superior vena cava occurs in 1-3% of the general pop- ulation [20, 21]. The persistent left superior vena cava lies lateral to the aortic arch and descends along the left side of the mediastinum, anterior to the left hilum, to enter the coro- nary sinus (Fig. 14). In most cases, there is an associated right superior vena cava, which is usually smaller than the left. The persistent left superior vena cava is usually an iso- lated finding, but it can be associated with congenital heart disease, usually atrial septal defects. The superior vena cava and coronary sinus may enhance intensely if contrast agent is injected into the left arm. The differential diagnostic con- siderations of the left superior vena cava include anomalous pulmonary venous drainage from the left upper lobe and su- perior intercostal vein, which is a normal finding.

Azygos Continuation of the Inferior Vena Cava

In azygos continuation of the inferior vena cava, the in- frahepatic segment of the inferior vena cava between the liver and renal veins fails to develop and the hemiazy- gos or azygos veins act as collateral vessels to return blood from the renal veins to the heart. The prevalence of this anomaly is about 0.6% [20, 22]. This anomaly may be isolated or associated with other anomalies, in- cluding situs abnormalities and polysplenia. CT find- ings include dilatation of the azygos arch, the azygos vein, and the superior vena cava caudal to the azygos junction, enlargement of the azygos and hemiazygos veins in the paraspinal and retrocrural areas, and ab- sence of the suprarenal and intrahepatic portions of the inferior vena cava (Fig. 15). The hepatic veins drain in- to the right atrium.

Fig. 14.Left superior vena cava. Sagittal multiplanar reformation shows the longitudinal course of the left superior vena cava (arrows), which extends from the left subclavian vein to the coronary sinus

Fig. 13. Pulmonary vein varix. Axial CT shows a dilated pulmonary vein (arrow) entering the left atrium (LA)

Fig. 15a, b.Azygos continuation of the inferior vena cava. a Contrast- enhanced CT demonstrates a dilated azygos vein arch (arrow) drain- ing into the superior vena cava (S). b A more caudal scan shows the dilated azygos vein (arrow) lateral to the descending aorta (A)

a

b

Congenital Heart Disease with Abnormal Vascular Connections

Truncus Arteriosus

In this malformation, a single arterial trunk with a single valve arises from the heart to supply the pulmonary, sys- temic, and coronary arteries. The pulmonary arteries can arise as a single short vessel from the posterior aspect of the truncus (type I, most common form) or they can have separate origins from the posterior aspect of the truncus (type II), sides of the truncus (type III), or the descend- ing aorta (type IV). Truncus arteriosus is one of the few cyanotic heart diseases in which CT can be used as the primary imaging study for diagnosis (Fig. 16).

Transposition of the Great Arteries

Dextro-transposition of the great arteries (D-TGA), also termed complete transposition, is an abnormality of ven- triculoarterial connection. The ascending aorta lies to the right and anterior to the pulmonary artery (Fig. 17). Levo-

transposition (L-transposition), also referred to as correct- ed transposition, is characterized by both ventriculoarter- ial and atrioventricular connections. The pulmonary artery arises from the anatomic left ventricle and the aorta from the anatomic right ventricle. The aorta lies anterior and to the right of the pulmonary artery (Fig. 18).

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Printed in March 2007