Lecture 3- Thoracic Aorta


Thoracic Aorta Segments

  • Divided into three main portions:

    • Ascending Aorta: starts in the middle mediastinum.

    • Arch of Aorta: continues from the ascending aorta.

    • Descending (Thoracic) Aorta: follows the arch.

Ascending Aorta

  • Length: ~5 cm; Diameter: ~2.5 cm.

  • Located intrapericardially below the transverse thoracic plane.

  • Ascends from the left ventricle to the sternal angle (CC3 to CC2).

  • Branches:

    • Right and left coronary arteries, which acquire blood during ventricular diastole.

Aortic Arch

Structure and Position

  • Curved continuation of the ascending aorta.

  • Arches superoposteriorly to the left, positioned behind the 2nd right sternocostal joint at the sternal angle.

  • Ends behind the 2nd left sternocostal joint(T4-T5)transitioning to the descending thoracic aorta.

  • Pulmonary trunk bifurcates beneath arch

  • Arches over left bronchus

Major Branches

  1. Brachiocephalic trunk

  2. Left common carotid artery

  3. Left subclavian artery

Brachiocephalic Trunk Details

  • Largest branch of the aorta, originates behind the manubrium of the sternum.

Aortic Arch Variations

  • Notable variations observed in a study of 1000 cadavers (Liechty et al., 1957), mostly relevant during surgery.

Subclavian Arteries

  • Divided into three parts by the scalenus anterior muscles:

    • 1st part: most branches arise here.

    • 2nd part: lies posterior to scalenus anterior.

    • 3rd part: continues as the axillary artery to the upper limb.

Ligamentum Arteriosum

  • An adult remnant of the ductus arteriosus, crucial for fetal circulation.

  • Connects the root of the pulmonary trunk to the aortic arch and closes after birth.

Recurrent Laryngeal Nerves

  • Positions differ between right and left due to embryological development.

  • The left recurrent laryngeal nerve has a longer course and is more susceptible to damage.

Clinical Observations

Coronary Artery Disease

  • Leading cause of global mortality.

  • Involves atherosclerotic plaques leading to reduced blood flow to the heart muscle.

  • Symptoms: Sudden chest pain, often radiating to the left arm or neck.

  • Treatment options: Stenting or bypass using grafts.

Ascending Aorta Aneurysm

  • Localized dilatation may occur; not reinforced by fibrous pericardium.

  • Risk of dissection or rupture: dissection refers to blood entering the wall of the aorta.

  • Associated with conditions like Marfan's syndrome.

Mediastinal Hematoma

  • Most commonly due to trauma (e.g., deceleration or blunt chest injuries).

Cardiac Tamponade

  • Occurs when fluid accumulation compresses the heart within the pericardial space.

Posterior Mediastinum

  • Location: anterior to T5-T12, positioned behind the pericardium and diaphragm, between the parietal pleurae.

Thoracic Aorta

  • Initiates on the left side at T4 and descends to T12.

  • Moves toward midline while remaining anterior to the vertebral column and displacing the esophagus to the right.

  • Surrounded by the thoracic aortic plexus and enters the abdomen through the aortic hiatus to continue as the abdominal aorta.

Thoracic Aorta Relations

  • Posterior: vertebrae and hemiazygos veins.

  • Anterior: root of the left lung, pericardium, left arteries, and esophagus from above down.

  • Right: Esophagus, thoracic duct, azygos veins.

  • Left: Left lung and pleura.

  • T12: Aortic hiatus (contains aorta, thoracic duct, azygos veins).

Thoracic Aorta Branches

  • To airways: bronchial arteries (1 right, 2 left).

  • To esophagus: middle esophageal arteries.

  • To mediastinum: branches to nodes and connective tissue.

  • To pericardium: pericardial branches.

  • To diaphragm: superior phrenic arteries.

  • To body wall: 9 pairs of posterior intercostal arteries (3rd – 11th intercostal spaces) and subcostal arteries.

Intercostal Arteries

  • Upper two posterior intercostal arteries originate from the supreme intercostal artery, a branch of the costocervical trunk from the subclavian artery.

Coarctation of the Aorta

  • Refers to the narrowing of a segment of the aorta.

  • Results in collateral circulation bringing blood through branches from the subclavian, internal thoracic, scapular, and intercostal arteries.

  • Classic signs include arterial hypertension in the right arm and normal pressure in lower extremities, along with a delay in radio-femoral pulse.