What is the development process of aortic arches?

Development of Aortic Arches

The development of aortic arches involves a complex transformation from initially symmetrical pharyngeal arch arteries to the asymmetrical great vessels of the adult circulation, with the most common configuration being a Type I arch where three major vessels originate directly from the aorta in approximately 70% of adults. 1

Normal Aortic Arch Development

Embryological Origin

• The aortic arch system develops from pharyngeal arch arteries that form in a cranial-to-caudal sequence within the pharyngeal mesenchyme
• Initially symmetrical vessels undergo remodeling to produce the asymmetrical brachiocephalic arteries seen in adults 2

Final Adult Configuration

• Type I arch (70% of population): Three major vessels originate directly from the aorta in the horizontal plane defined by the outer curvature of the arch 1
• The standard configuration includes:
  • Brachiocephalic (innominate) artery
  • Left common carotid artery
  • Left subclavian artery

Common Aortic Arch Variants

Bovine Arch

• Most common variant (22% of population) 1
• Two types:
  • Type II-A (9%): Left common carotid artery arises from the innominate artery
  • Type II-B (13%): Innominate and left common carotid arteries arise from a common origin 1
• Clinical significance: Associated with higher risk of aortic dilation, dissection, and more rapid aortic expansion 1
  • Bovine arch was highly predictive of arch tear in type A aortic dissection (OR 5.9)
  • Annual aortic growth rate was 0.29 cm/y with bovine arch vs. 0.09 cm/y with normal anatomy 1

Aberrant Subclavian Artery

• Most common variant is aberrant right subclavian artery, arising as the last branch of the aortic arch
• Often passes behind the esophagus, potentially causing dysphagia lusoria or respiratory symptoms
• Aberrant left subclavian artery is less common and typically associated with congenital heart defects 1

Kommerell's Diverticulum

• Remnant of the fourth dorsal aortic arch due to incomplete regression
• Found in 20-60% of those with an aberrant subclavian artery
• Surgical intervention advised when diverticulum orifice >30 mm or combined diverticulum and adjacent descending aorta diameter >50 mm 1

Type Classification of Aortic Arches

Type I Arch

• All three major vessels originate in the horizontal plane defined by the outer curvature of the arch 1

Type II Arch

• Brachiocephalic artery originates between the horizontal planes of the outer and inner curvatures of the arch 1

Type III Arch

• Brachiocephalic artery originates below the horizontal plane of the inner curvature of the arch 1

Clinical Implications

Anatomical Variations and Pathology

• Bovine arch variants appear to be markers for thoracic aortic disease and more rapid aortic expansion 1
• Some variations may predispose to aneurysm formation, dissection, and rupture during endovascular procedures 3

Collateral Circulation

• Important collateral pathways exist between the external carotid artery and internal carotid artery:
  • Via the internal maxillary branch of the external carotid artery
  • Via the superficial temporal artery to the ophthalmic branches of the internal carotid artery 1, 4
• Additional collateral pathways:
  • From external carotid artery to vertebral artery (via the occipital branch)
  • From vertebrobasilar system to internal carotid artery (via posterior communicating artery)
  • Between left and right internal carotid arteries (via anterior communicating artery) 1, 4

Diagnostic Considerations

• Cross-sectional imaging with CT or MRI is essential for accurate diagnosis and evaluation of aortic arch anomalies 5
• Understanding embryological development helps in classifying various subtypes of aortic arch anomalies and variants 5

Management Implications

• In patients with bovine arch, imaging to assess for thoracic aortic aneurysm may be reasonable (Class IIb recommendation) 1
• Understanding aortic arch variants is crucial for planning endovascular procedures and interpreting imaging studies 4, 3

Understanding the development and variations of aortic arches is essential for recognizing potential pathologies and planning appropriate interventions, particularly in patients with variants that may predispose to aortic disease.