Summary
Highlights
The video introduces the four main arterial groups that irrigate the thoracic wall: internal mammary arteries, superior intercostal arteries, posterior intercostal arteries, and subcostal arteries. It also notes that venous drainage follows similar naming conventions.
The internal mammary artery, also known as the internal thoracic artery, is a branch of the subclavian artery. It descends, resting on the pleural cupula, then runs anterior to the costal parietal pleura and between the costal cartilages. It passes in front of the transversus thoracis muscle and terminates at the sixth intercostal space, dividing into the superior epigastric artery and the musculophrenic artery.
The internal mammary artery gives off several branches: the pericardiacophrenic artery (accompanying the phrenic nerve to irrigate the pericardium, parietal pleura, and diaphragm), anterior intercostal arteries (superior and inferior branches for each of the first six intercostal spaces), and anterior perforating branches (going forward into the chest, particularly for the mammary gland in the 2nd, 3rd, and 4th spaces).
The musculophrenic artery is considered a continuation of the internal mammary artery, supplying the anterior intercostal arteries and anterior perforating branches for the 7th, 8th, and 9th intercostal spaces after the internal mammary artery terminates.
The posterior thoracic wall is irrigated by posterior intercostal arteries. The first two posterior intercostal arteries are branches of the superior intercostal artery, which itself is a branch of the costocervical trunk from the subclavian artery. From the third to the eleventh intercostal spaces, the posterior intercostal arteries are direct branches of the thoracic aorta.
Due to the thoracic aorta's position on the left, right posterior intercostal arteries are longer. Each posterior intercostal artery gives a dorsal branch (subdividing into spinal and muscular branches) and a ventral branch (the proper intercostal artery). The muscular branch further divides into medial cutaneous and external branches. The main ventral branch also gives a collateral branch that anastomoses with the inferior branch of the anterior intercostal artery, while its superior branch anastomoses with the anterior intercostal artery itself.
The subcostal artery is the twelfth posterior intercostal artery but is named subcostal because it runs below the twelfth rib, not between intercostal spaces. Additionally, the video mentions bronchial arteries: two left bronchial arteries (direct branches of the thoracic aorta) and one right bronchial artery, which is a branch of the third right posterior intercostal artery.
Anterior intercostal veins join to form satellite veins, which then form the internal mammary vein (or internal thoracic vein). This vein drains directly into the brachiocephalic venous trunks.
The posterior venous drainage is more complex. On the right side, the superior intercostal vein drains the first three or four intercostal spaces and empties into the azygos vein. The remaining posterior intercostal veins on the right also drain directly into the azygos vein.
On the left side, the superior intercostal vein drains the first three or four intercostal spaces but empties into the left brachiocephalic vein. The intercostal veins from the 4th to 7th spaces form the accessory hemiazygos vein, which typically crosses the midline to drain into the azygos vein. The more inferior intercostal veins (8th to 11th) form the hemiazygos vein, which also crosses the midline to drain into the azygos vein. The subcostal vein assists in forming the azygos vein on the right and the hemiazygos vein on the left.