Chapter30 Aorta

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Chapter 30: Thoracic Aorta

L common carotid

*

L subclavian

*

Brachiocephalic

Figure 30.9.  Two-Vessel Arch. 3D volume-rendered image of the aortic arch shows common origin ( * ) of the brachiocephalic artery and left common carotid artery.

Figure 30.8.  Sagittal MIP CT demonstrates focal narrowing of the distal aortic arch corresponding to the aortic isthmus ( black arrow ), just distal to the left subclavian artery takeoff (*). Note the focal prom- inence of the aorta ( dashed line ) at the origin of the ligamentum arte- riosum ( white arrow ) which extends toward the left pulmonary artery. This is often referred to as a “ductus bump” or “ductus diverticulum.”

diverticulum of Kommerell and vascular ring, an aberrant right subclavian artery is typically asymptomatic, but about 10% of patients can have dysphagia (aka “dysphagia luso- ria”) secondary to extrinsic compression of the esophagus. Right Arch Variants Right aortic arch has a prevalence of 0.05%. On frontal pro- jection chest radiograph, the normal indentation of the left aortic arch on the left aspect of the trachea is absent, replaced

abutting the left aspect of the thoracic spine and becoming the abdominal aorta at the diaphragmatic hiatus.

Left Arch Variants Left aortic arch variants are common incidental findings usu- ally of little clinical significance. Two-vessel aortic arch is characterized by common origin of the right brachiocephalic and left common carotid arteries and occurs in 13% to 20% of the population (Fig. 30.9). Although this is often termed a “bovine arch,” this is a misnomer as a true bovine arch has only a single vessel from the aortic arch. A four-vessel arch in which the left vertebral artery has an independent origin from the aortic arch occurs in 5% to 6% of the population. In this case, the left vertebral artery originates between the left com- mon carotid and subclavian arteries (Fig. 30.10). Left aortic arch with aberrant right subclavian artery has a prevalence of 0.5% to 2%. Instead of the normal origin from the right brachiocephalic artery, the right subclavian artery arises distal to the left subclavian artery from the distal aortic arch and travels through the mediastinum behind the esophagus to supply the right upper extremity. On esopha- gram, the aberrant subclavian artery indents the posterior aspect of the esophagus (Fig. 30.11). In approximately 15% of cases, the aberrant right subclavian artery is associated with an aneurysm at its origin, termed a diverticulum of Kommerell. The diverticulum of Kommerell is an embryologic remnant of the dorsal aortic arch and can cause compressive symptoms on the esophagus if large. However, in most instances of an aberrant right subclavian artery, this diverticulum is absent or small. Additionally, this configuration does not form a vascu- lar ring in the vast majority of instances. Only in the setting of a very rare right ligamentum arteriosum, which is a fibrous remnant of the ductus arteriosum, does a vascular ring occur with an aberrant right subclavian artery. In the absence of a

2 3 4

1

Figure 30.10.  Four-Vessel Arch. Oblique sagittal MIP CT demon- strates separate origin of the left vertebral artery ( 3 ) between the left common carotid artery ( 2 ) and left subclavian artery ( 4 ). The brachio- cephalic artery ( 1 ) is the first branch off the arch.