QS Study

The thoracic cage or wall is the skeleton of the thoracic wall. It is formed by the 12 thoracic vertebrae, 12 pairs of ribs and associated costal cartilages and the sternum. It has a significant role play for raising or reducing the intrathoracic pressure to ensure a crucial mechanism of respiration.

Arterial supply of thoracic wall: a Thoracic wall is supplied by anterior and posterior intercostal arteries. Each intercostal space contains:

  1. Two anterior intercostal arteries – The two internal thoracic arteries can be differentiated as left and right. One on either side of the sternum and is located deep towards the anterior chest wall.
  2. One posterior intercostal artery – here are 11 arteries on each side, 1 on each space.

(i) Anterior intercostal artery: It finishes in the 6th intercostal space by breaking up into superior epigastric and musculophrenic arteries.

Number

9 pairs on each side, 1 pair on each intercostal space, 10th and 11th spaces don’t have any.

Origin

(1) 1st – 6th arise from the internal thoracic artery, which is a branch of 1st part of the subclavian artery.

(2) 7th – 9th arise from a musculophrenic artery, a branch of the internal thoracic artery.

Fig – Arterial supply of the thoracic wall

(ii) Posterior intercostal artery:

Number

11 on each side, one in each intercostal space.

Origin

  • 1 st and 2nd arise from the superior intercostal artery, a branch of costocervical trunk.
  • Others arise from descending thoracic aorta. In lower 9 spaces, they arise from descending thoracic aorta.

Branches

  1. A dorsal branch.
  2. A collateral branch.
  3. Muscular arteries.
  4. A lateral cutaneous branch.
  5. Mammary branches.
  6. Right bronchial artery.

Venous drainage

Thoracic wall is drained by anterior and posterior intercostal veins.  There are 2 anterior intercostal veins in each of the 9 spaces. From upper 6 spaces the veins drain into internal thoracic vein & the lower 3 spaces they drain into the musculophrenic vein.

(A) Anterior intercostal vein: The anterior intercostal veins originate from the intercostal space just inferior to anterior aspects of their respective ribs and drain into the internal thoracic and musculophrenic veins.

Number

9 pairs on each side, 1 pair in each intercostal space, 10th Sc 11 th spaces don’t have any. There are 11 posterior intercostal veins, 1 on each intercostal space. The mode of termination of the posterior intercostal veins is different in right & left side.

Termination

(i) 1st to 6th drain into an internal thoracic vein.

(ii) 7th to 9th drain into a musculophrenic vein.

(B) Posterior intercostal vein: The posterior aspect is drained by the azygos system into the SVC. The posterior intercostal veins originate from the intercostal space just inferior to posterior aspects of their respective ribs

Number – One in each intercostal space. In the right side, the 4th to 11th posterior intercostal veins and subcostal vein drain into the azygos vein.