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Intercostal veins
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.
Anatomy
Topography
The 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. An easy way to remember this is to learn the mnemonic VAN (from superior to inferior: Vein, Artery and Nerve).
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.
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Drainage
The posterior intercostal veins drain into the azygos (right side) and hemiazygos and accessory hemiazygos vein (left side). The name azygos originates from the Greek word ‘Zyg’ meaning paired and A means not. The azygos vein does not have a pair (instead there are two separate veins that drain the left posterior thorax and abdomen i.e. the hemiazygos and accessory hemiazygos). The posterior intercostal vein of the first space drains into vertebral vein or brachiocephalic vein of the same side.
The superior intercostal vein is formed by the union of second, third and sometimes fourth posterior intercostal veins which drain into azygos vein on right side and left brachiocephalic vein on left side. The 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 the azygos and left sided drain into hemiazygos and accessory hemiazygos veins.
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The azygos 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 azygos vein arches over the right main bronchus, in order to join the superior vena cava. The azygos vein also drains the pericardial veins, bronchial veins and vertebral venous plexuses.
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The hemiazygos vein mirrors the lower part of the azygos vein, and receives the 9th to 11th posterior intercostal veins as well as the subcostal vein. The accessory hemiazygos vein receives posterior intercostal veins from 4th to 8th space and left bronchial veins. The hemiazygos and accessory hemiazygos vein drain into the azygos vein at the level of T7-8 that drains into the superior vena cava (at T5-T6).
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Clinical aspects
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 azygos 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.
Summary
- 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 azygos vein (right side), and hemiazygos and accessory hemiazygos veins (left side). The latter two veins ultimately drain into the azygos vein.
- The azygos vein then drains into the superior vena cava.
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