The intercostal space is the space between the ribs, and it is comprised of three muscular layers and a neurovascular bundle which runs between the intermediate and inner layers of these muscles. In this article we will discuss the gross and functional anatomy of the intercostal veins. We will also discuss the clinical relevance of the structure, and provide a summary of key points at the end of the article. We will finally conclude with some review questions to test the reader’s understanding of the article content.
AnatomyThe neurovascular bundle of each rib consists of the intercostal artery, vein and nerve. The neurovascular bundle runs directly under the lower border of each rib. The vein is the superior most of the three, with the artery below, and the nerve lowest.
Each space contains one posterior and two anterior intercostal veins which runs with the arteries of the same name. The anterior intercostal veins follow the same course as the arteries, and drain into internal thoracic and musculophrenic veins.
The posterior intercostal veins drain into the azygous (right side) and hemiazygous and accessory hemiazygous vein (left side). The name azygous originates from the Greek word ‘Zyg’ meaning paired and A means not. The azygous vein does not have a pair (instead there are two separate veins that drain the left posterior thorax and abdomen i.e. the hemiazygous and accessory hemiazygous). Posterior intercostal vein of the first space drains into vertebral vein or brachiocephalic vein of the same side. Superior intercostal vein is formed by the union of second, third and sometimes fourth posterior intercostal veins which drain into azygous vein on right side and left brachiocephalic vein on left side. Left superior intercostal vein passes over the arch of aorta medial to phrenic and lateral to vagus nerve on its way to brachiocephalic. In the remaining lower eight spaces right sided posterior intercostal veins open into azygous and left sided drain into hemiazygous and accessory hemiazygous. The azygous vein drains the posterior thoracic and abdominal wall, and is formed by the confluence of the ascending lumbar veins and the right subcostal vein at vertebral level T12. The azygous vein arches over the right main bronchus, in order to join the superior vena cava. The azygous vein also drains the pericardial veins, bronchial veins and vertebral venous plexuses.
The hemiazygous vein mirrors the lower part of the azygous vein, and receives the 9th to 11th posterior intercostal veins as well as the subcostal vein. The accessory hemiazygous vein receives posterior intercostal veins from 4th to 8th space and left bronchial veins. The hemiazygous and accessory hemiazygous vein drain into the azygous vein at the level of T7-8 that drains into the superior vena cava (at T5-T6).
Pleural drain- For pleural drainage a needle is inserted just above the rib in order to avoid damage to the neurovascular bundle which runs at the lower border of the rib.
Enlarged azygous vein- This can result from overhydration, pregnancy, aortoazygous fistula, constrictive pericarditis, Superior vena cava obstruction, inferior vena cava obstruction, portal hypertension and any other cause of right heart output failure. CT scan is useful technique to diagnose this condition and can also be useful to evaluate the etiology.
- The anterior intercostal veins follow the arteries.
- The intercostal veins run above the intercostal arteries, which run above the intercostal nerves.
- The posterior intercostal veins drain into the azygous vein (right side), and hemiazygous and accessory hemiazygous veins (left side). The latter two veins ultimately drain into the azygous vein.
- The azygous vein then drains into the superior vena cava.