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Topic

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Aortic arch

The aortic arch is the curved segment of the thoracic aorta that connects the ascending aorta to the descending thoracic aorta. It is the principal arterial conduit supplying blood to the head, neck, and upper limbs through its major branches.

It is a central structure in thoracic anatomy, cardiovascular imaging, and surgical planning and serves as a key landmark in mediastinal evaluation.

Synonyms

  • Arcus aortae

  • Arch of the aorta

Location

  • Located in the superior mediastinum

  • Begins at the level of the sternal angle (T4–T5)

  • Arches posteriorly, superiorly, and to the left

  • Ends as the descending thoracic aorta

  • Anterior to the tracheal bifurcation

  • Superior to the pulmonary artery bifurcation

  • Left of the trachea and esophagus

Anatomical components

  • Proximal segment:

    • Continuation of the ascending aorta

  • Convex superior surface:

    • Gives rise to major arterial branches

  • Distal segment:

    • Continuous with the descending thoracic aorta

Branches

  • Brachiocephalic trunk:

    • Divides into right common carotid and right subclavian arteries

  • Left common carotid artery

  • Left subclavian artery

Relations

Anteriorly:

  • Manubrium sterni

  • Left brachiocephalic vein

  • Left phrenic nerve and vagus nerve

Posteriorly:

  • Trachea

  • Esophagus

  • Thoracic duct

Inferiorly:

  • Pulmonary artery bifurcation

  • Left main bronchus

Superiorly:

  • Thymic remnants (in adults)

  • Superior mediastinal fat

Laterally:

  • Left lung and pleura

Structures related to the aortic arch

  • Ligamentum arteriosum

  • Left recurrent laryngeal nerve looping beneath the arch

  • Aortic arch lymph nodes

  • Pulmonary artery

Function

  • Systemic distribution: Conducts oxygenated blood from the heart to the body

  • Cerebral and upper limb supply: Provides arterial inflow via its major branches

  • Hemodynamic regulation: Acts as an elastic reservoir smoothing systolic flow

X-ray appearance

Chest radiograph (PA view):

  • Aortic knuckle: Smooth convex contour along the left mediastinal border

  • Arch shadow: Forms the upper left mediastinal outline

  • Position: Seen above the left hilum

  • Silhouette: Well-defined interface with lung

CT appearance

Pre-contrast CT:

  • Aortic lumen: Homogeneous soft-tissue density blood column

  • Aortic wall: Thin, smooth contour

  • Calcification: May be seen in the wall in older individuals

  • Relationship: Clear interface with trachea, esophagus, and pulmonary artery

  • Mediastinal fat planes: Preserved around the arch

Post-contrast CT:

  • Aortic lumen: Intense homogeneous enhancement of contrast-opacified blood

  • Aortic wall: Thin enhancing rim

  • Branch vessels: Well-opacified origins of brachiocephalic, left common carotid, and left subclavian arteries

  • Contour: Smooth, continuous vascular outline

  • Surrounding mediastinum: Clear separation from adjacent structures

MRI appearance

T1-weighted images:

  • Aortic lumen: Flow void or low signal due to rapid blood flow

  • Aortic wall: Thin low-signal rim

  • Surrounding fat: High signal outlining the vessel

T2-weighted images:

  • Aortic lumen: Flow-related signal void or low signal

  • Wall: Low-to-intermediate signal

  • Adjacent mediastinal structures: Intermediate signal

STIR:

  • Aortic lumen: Signal void from flowing blood

  • Mediastinal fat: Suppressed signal

  • Vessel outline: Well delineated against suppressed background

Post-contrast T1-weighted GRE:

  • Aortic lumen: Bright, homogeneous enhancement

  • Aortic wall: Thin enhancing margin

  • Branch origins: Clearly visualized with high spatial resolution

  • Flow-related effects: Minimal signal loss with appropriate timing

  • Utility: Excellent for delineating arch contour and branch anatomy

CT image

Aortic arch CT AXIAL IMAGE

CT image

Aortic arch CT SAG