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The thoracic aorta is subdivided into 3 sections: the ascending aorta, the aortic arch, and the descending aorta (see Image. Thoracic Aorta and the Aortic Arch, Computed Tomography Angiography). The ascending thoracic aorta arises from the left ventricle of the heart, anterior to the pulmonary artery, and rises to approximately the level of the fourth thoracic vertebra. The aorta then begins to travel posteriorly and to the left, where it is known as the arch of the aorta. The normal aortic arch gives rise to 3 vessels. The brachiocephalic trunk, also known as the innominate artery, is the first branch, bifurcating into the right subclavian and right common carotid artery. The brachiocephalic trunk is then followed by the left common carotid and subclavian arteries. The 'typical' pattern of aortic arch vessels occurs in approximately 70% of the population. Around the vertebral level of T4, the aorta continues as the descending thoracic aorta until it reaches the diaphragm.[1][2] Development of the Thoracic Aorta The ascending aorta develops as a component of the primitive heart tube. The primitive heart develops from 5 dilations: the truncus arteriosus, conus cordis, primitive ventricle, primitive atrium, and the sinus venosus. The truncus arteriosus forms the basis for developing the ascending aorta and pulmonary trunk, beginning during the fifth week of development. The truncus starts as a single outflow tract from the right and left ventricles but is eventually divided by the aorticopulmonary septum into separate vascular outflow channels. The truncal and conal ridges are invaded by neural crest cells, leading to spiraling that forms the aorticopulmonary septum.[3] The aortic arch develops from multiple structures. The portion of the arch proximal to the brachiocephalic trunk arises directly from the aortic sac. The medial area of the arch, between the brachiocephalic trunk and the left common carotid artery, arises from the left fourth aortic arch. The portion of the arch distal to the left common carotid artery arises from the dorsal aorta.

The aortic arch develops from multiple structures. The portion of the arch proximal to the brachiocephalic trunk arises directly from the aortic sac. The medial area of the arch, between the brachiocephalic trunk and the left common carotid artery, arises from the left fourth aortic arch. The portion of the arch distal to the left common carotid artery arises from the dorsal aorta. The descending aorta arises from the dorsal aorta. Early in development, the paired right and left dorsal aortae are confluent with the aortic sac. The right and left dorsal aortae later fuse along vertebral levels T4 to L4, forming a single, continuous dorsal aorta. The dorsal aorta ultimately gives rise to numerous vital branches, including intersegmental, splanchnic (visceral), and umbilical arteries.[4] The dorsal aorta in this region is later referred to as the descending thoracic and abdominal aorta.

Due to the complexity of aortic arch development, numerous congenital abnormalities are possible. Malformations result from the persistence of structures that typically regress, or from the regression of structures that typically persist.[6] Abnormalities of Aortic Arch Vessels Common Origin of Brachiocephalic Trunk and Left Common Carotid Artery - Instead of arising from the arch of the aorta as distinct branches, the left common carotid artery and the brachiocephalic trunk both arise from a common origin. In this variant, only 2 vessels (the common trunk and the left subclavian) branch directly off the arch of the aorta. This arrangement is the second most common branching pattern, following the 'normal' pattern detailed above, occurring in approximately 13% of the population.[7] This pattern is often incorrectly termed the 'bovine aortic arch.' A true bovine arch consists of a single vessel arising from the aortic arch. This vessel gives rise to the subclavian arteries bilaterally and to a common carotid trunk, which bifurcates into the right and left common carotid arteries. This vessel pattern is not present in humans. Origin of Left Common Carotid Artery from the Brachiocephalic Trunk - This pattern is very similar to the typical origin pattern detailed above. Two vessels arise from the arch of the aorta: the brachiocephalic trunk and the left common carotid artery. However, in this situation, the left common carotid artery arises distally, directly from the brachiocephalic trunk rather than from a common origin. Typically, the common carotid originates less than 1 cm from the aortic arch.[7]

Origin of Left Common Carotid Artery from the Brachiocephalic Trunk - This pattern is very similar to the typical origin pattern detailed above. Two vessels arise from the arch of the aorta: the brachiocephalic trunk and the left common carotid artery. However, in this situation, the left common carotid artery arises distally, directly from the brachiocephalic trunk rather than from a common origin. Typically, the common carotid originates less than 1 cm from the aortic arch.[7] Aberrant Right Subclavian Artery (ARSA) - Occurring in approximately 1% of the population, the right subclavian artery is the final branch arising off the aortic arch, occurring distal to the takeoff of the left subclavian artery. This formation results from abnormal regression of the right fourth aortic arch, causing loss of the normal proximal portion of the right subclavian artery. The artery arises entirely from the right seventh segmental artery, from the dorsal aorta. To reach the right upper extremity, the aberrant artery most commonly (80% of cases) crosses the midline posterior to the esophagus. The other routes are between the trachea and esophagus (15% of cases) and anterior to the trachea (5%). This condition is generally asymptomatic but can cause esophageal compression or dysphagia, stridor, or recurrent laryngeal nerve compression. One case report describes retroesophageal ARSA presenting with tracheoesophageal fistula formation, suspected to be secondary to chronic compression.[8] Anomalous Origin of Vertebral Artery - In approximately 5% of cases, the left vertebral artery arises from the aortic arch, frequently between the left common carotid and subclavian arteries. The proximal portion can be duplicated, arising from the aortic arch and the left subclavian artery, before merging into a single artery.[9] There have been case reports of bilateral vertebral arteries arising from the aortic arch, both arising between the left common carotid and left subclavian arteries, both arising distal to the left subclavian artery, or the left vertebral artery originating between the left common carotid and left subclavian artery while the right vertebral artery originates distal to the left subclavian artery.[10][11][12]

Anomalous Origin of Vertebral Artery - In approximately 5% of cases, the left vertebral artery arises from the aortic arch, frequently between the left common carotid and subclavian arteries. The proximal portion can be duplicated, arising from the aortic arch and the left subclavian artery, before merging into a single artery.[9] There have been case reports of bilateral vertebral arteries arising from the aortic arch, both arising between the left common carotid and left subclavian arteries, both arising distal to the left subclavian artery, or the left vertebral artery originating between the left common carotid and left subclavian artery while the right vertebral artery originates distal to the left subclavian artery.[10][11][12] Patent Ductus Arteriosus - The ductus arteriosus arises from the dorsal left sixth aortic arch and connects the pulmonary artery to the aorta. This connection is an important aspect of fetal circulation, allowing oxygenated blood to bypass the fluid-filled lungs that do not participate in gas exchange. The ductus arteriosus typically closes in the first 3 days of life, forming a fibrous cord called the ligamentum arteriosum. When the ductus fails to close, it creates a left-to-right shunt because the systemic circulation has higher resistance than the pulmonary circulation. If the defect is large enough, it can lead to pulmonary hypertension and early-onset heart failure. The risk of a persistent ductus arteriosus increases with decreasing birth weight. PDA classically presents with a continuous 'machine-like' murmur radiating to the back.[13][14] Abnormalities of the Arch of the Aorta Truncus Arteriosus - A rare congenital heart defect presenting with a common ventricular outflow tract and a ventricular septal defect. It results from abnormal aorticopulmonary septum formation, frequently attributed to impaired neural crest cell migration. It is frequently associated with 22q11 gene deletions or mutations. During early life, pulmonary vascular resistance is relatively high, leading to right-to-left shunting and cyanosis in the infant. These defects require early surgical repair within the first month of life.[15]

Truncus Arteriosus - A rare congenital heart defect presenting with a common ventricular outflow tract and a ventricular septal defect. It results from abnormal aorticopulmonary septum formation, frequently attributed to impaired neural crest cell migration. It is frequently associated with 22q11 gene deletions or mutations. During early life, pulmonary vascular resistance is relatively high, leading to right-to-left shunting and cyanosis in the infant. These defects require early surgical repair within the first month of life.[15] Coarctation of the Aorta - An area of stenosis in the aorta, most commonly in the thoracic aorta, but it can also occur in the abdominal aorta. This anomaly occurs in less than 0.1% of the population. They are classified as pre-ductal or post-ductal. Post-ductal lesions are the most common and occur distal to the ductus arteriosus. Pre-ductal lesions occur less commonly and present proximally to the ductus arteriosus. Traditionally, coarctation is classified as infantile (pre-ductal) or adult (post-ductal), but this classification has been abandoned because age at presentation is more closely related to stenosis severity than to location. The most common presentation is a difference in blood pressure between the upper and lower extremities. Coarctation is repairable with surgical removal of the stenotic segment or transcatheter stenting.[16] There have also been reports of coarctation in right-sided aortic arches.[17]

Coarctation of the Aorta - An area of stenosis in the aorta, most commonly in the thoracic aorta, but it can also occur in the abdominal aorta. This anomaly occurs in less than 0.1% of the population. They are classified as pre-ductal or post-ductal. Post-ductal lesions are the most common and occur distal to the ductus arteriosus. Pre-ductal lesions occur less commonly and present proximally to the ductus arteriosus. Traditionally, coarctation is classified as infantile (pre-ductal) or adult (post-ductal), but this classification has been abandoned because age at presentation is more closely related to stenosis severity than to location. The most common presentation is a difference in blood pressure between the upper and lower extremities. Coarctation is repairable with surgical removal of the stenotic segment or transcatheter stenting.[16] There have also been reports of coarctation in right-sided aortic arches.[17] Interrupted Aortic Arch (IAA) - A severe version of coarctation of the aorta, which presents with a complete luminal interruption between the ascending and descending aorta. This malformation is incompatible with life in the absence of a patent ductus arteriosus, which is required for left ventricular outflow and systemic blood flow. Interrupted arches get classified by the site of disruption, with type A occurring distal to the left subclavian (13% of cases), type B between the left subclavian and left common carotid (84% of cases), and type C occurring proximal to the left common carotid artery. IAA most commonly presents in infancy due to absent blood flow to the extremities. PGE1 is necessary to maintain patency of the ductus arteriosus, which requires surgical repair.[18] One case report details a case of isolated Type B IAA discovered in a 70-year-old patient who had never undergone intervention. CTA demonstrated extensive collateral blood flow, and conservative therapy was followed.[19]

Interrupted Aortic Arch (IAA) - A severe version of coarctation of the aorta, which presents with a complete luminal interruption between the ascending and descending aorta. This malformation is incompatible with life in the absence of a patent ductus arteriosus, which is required for left ventricular outflow and systemic blood flow. Interrupted arches get classified by the site of disruption, with type A occurring distal to the left subclavian (13% of cases), type B between the left subclavian and left common carotid (84% of cases), and type C occurring proximal to the left common carotid artery. IAA most commonly presents in infancy due to absent blood flow to the extremities. PGE1 is necessary to maintain patency of the ductus arteriosus, which requires surgical repair.[18] One case report details a case of isolated Type B IAA discovered in a 70-year-old patient who had never undergone intervention. CTA demonstrated extensive collateral blood flow, and conservative therapy was followed.[19] Right-Sided Aortic Arch - An uncommon anomaly (presenting in less than 0.1% of the population) where the aortic arch traverses the right bronchus instead of the left bronchus. This condition occurs due to the persistence of the right dorsal aorta with the regression of the left dorsal aorta. The most common presentation (approximately 60%) is the 'mirror-type,' with a right-sided arch and a left brachiocephalic trunk, right common carotid, and right subclavian arteries. The 'mirror type' is strongly associated with other congenital heart defects. The next most common presentation (approximately 40%) is a right-sided aortic arch with an aberrant left subclavian artery; this mimics the ARSA pattern, with the left common carotid arising first, followed by the right common carotid, right subclavian, and then left subclavian arteries. As with traditional ARSA, this leads to the formation of a vascular ring and symptoms of tracheal or esophageal compression. Patients with a right-sided arch but a left-sided ligamentum arteriosum may also present with symptoms of a vascular ring.[20] See Image. Right Aortic Arch.

Right-Sided Aortic Arch - An uncommon anomaly (presenting in less than 0.1% of the population) where the aortic arch traverses the right bronchus instead of the left bronchus. This condition occurs due to the persistence of the right dorsal aorta with the regression of the left dorsal aorta. The most common presentation (approximately 60%) is the 'mirror-type,' with a right-sided arch and a left brachiocephalic trunk, right common carotid, and right subclavian arteries. The 'mirror type' is strongly associated with other congenital heart defects. The next most common presentation (approximately 40%) is a right-sided aortic arch with an aberrant left subclavian artery; this mimics the ARSA pattern, with the left common carotid arising first, followed by the right common carotid, right subclavian, and then left subclavian arteries. As with traditional ARSA, this leads to the formation of a vascular ring and symptoms of tracheal or esophageal compression. Patients with a right-sided arch but a left-sided ligamentum arteriosum may also present with symptoms of a vascular ring.[20] See Image. Right Aortic Arch. Double Aortic Arch - A rare malformation of the aorta, with a division of the ascending aorta into 2 arches. These arches generally surround the trachea/esophagus, forming a vascular ring, which most commonly results from persistence of the right fourth aortic arch. Generally, the arches are asymmetric, with 70% right-sided dominant and 25% left-sided dominant. Balanced arches occur in only 5% of cases, and the typical presentation in the neonate is with symptoms of esophageal or tracheal compression (swallowing disorders, expiratory stridor). Swallowing difficulty can present with respiratory symptoms secondary to recurrent aspiration. Surgical division of the vascular ring is indicated for symptomatic patients; however, persistent respiratory symptoms are common due to abnormal tracheal development.[21][22] See Image. Cardiac Computed Tomography, Double Aortic Arch.

Double Aortic Arch - A rare malformation of the aorta, with a division of the ascending aorta into 2 arches. These arches generally surround the trachea/esophagus, forming a vascular ring, which most commonly results from persistence of the right fourth aortic arch. Generally, the arches are asymmetric, with 70% right-sided dominant and 25% left-sided dominant. Balanced arches occur in only 5% of cases, and the typical presentation in the neonate is with symptoms of esophageal or tracheal compression (swallowing disorders, expiratory stridor). Swallowing difficulty can present with respiratory symptoms secondary to recurrent aspiration. Surgical division of the vascular ring is indicated for symptomatic patients; however, persistent respiratory symptoms are common due to abnormal tracheal development.[21][22] See Image. Cardiac Computed Tomography, Double Aortic Arch. Persistent Fifth Aortic Arch (PFAA) - This is a rare congenital condition where the fifth aortic arch fails to degenerate unilaterally.[23] Some suspect that the condition is underrecognized rather than truly uncommon.[24] Others doubt that the condition exists at all.[25] PFAA can present in 2 primary fashions. In the first type, the persistent arch connects the ascending and descending aorta underneath the fourth arch. This results in a double aortic arch that does not encircle the trachea or esophagus. This type has limited functional or hemodynamic consequences. One case report details a case of a PFAA in a patient associated with aortic coarctation. The surgical repair involved a side-to-side anastomosis, thereby enlarging the coarctation and eliminating the double aortic arch.[26] In the second type, the persistent fifth arch fuses with a portion of the sixth aortic arch, resulting in a systemic-pulmonary shunt. It most commonly occurs in conjunction with other congenital heart defects, including pulmonary atresia and truncus arteriosus. Thus, the shunt is beneficial because it increases blood flow to the pulmonary system in these conditions. In patients without an associated defect, this shunt can lead to heart failure in patients as young as 2 months.[27]

In the second type, the persistent fifth arch fuses with a portion of the sixth aortic arch, resulting in a systemic-pulmonary shunt. It most commonly occurs in conjunction with other congenital heart defects, including pulmonary atresia and truncus arteriosus. Thus, the shunt is beneficial because it increases blood flow to the pulmonary system in these conditions. In patients without an associated defect, this shunt can lead to heart failure in patients as young as 2 months.[27] There have been suggestions that rare cases of the left pulmonary artery arising from the ascending aorta can be attributed to PFAA. The belief is that the sixth aortic arch fails to develop, and the left fifth aortic arch persists, resulting in an anomalous pulmonary artery.[28] One case report details a patient with a double-lumen aortic arch and an anomalous left pulmonary artery originating from the ascending aorta. The authors suggest it is a case of bilateral PFAA, with the right fifth aortic arch forming the double-lumen aorta and the left fifth aortic arch forming the anomalous pulmonary artery.[29] Cervical Aortic Arch - A rare aortic arch anomaly with a very high location of the aortic arch; this occurs due to the persistence of the third aortic arch, with regression of the fourth aortic arch during development. The arch is typically located in the mid-neck and commonly presents with a right-sided aortic arch. These are frequently asymptomatic but may present with tracheal compression, esophageal compression, or a pulsatile neck mass.[30][31]