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Veins - Trunk & Abdominal Walls

Veins of the Trunk

Here we’ll learn about venous drainage of the thoracic and abdominal walls; we’ll focus on the posterior wall veins because the anterior vessels mirror the arterial pathways.

Be aware that there is extensive variation in venous pathways, particularly in the posterior wall.

Overview

We’ll begin with an overview of key veins, then we’ll draw them in anatomical context; notice which veins are paired and symmetrical, and which veins are not.

Starting distally:

The common iliac veins drain into the inferior vena cava.
The iliolumbar veins and the ascending lumbar veins.
At their proximal ends, the ascending lumbar veins meet the subcostal veins.
On the right side only, these two veins drain into the azygos vein, which ascends along the posterior trunk wall and empties into the superior vena cava.
On the left side only, the ascending lumbar and subcostal veins drain into the hemiazygos vein, which ascends along the trunk wall before traveling to the right and draining into the azygos vein.
The accessory hemiazygos vein arises superiorly and descends to drain into the azygos vein.
The superior vena cava receives the right and left brachiocephalic veins.
On the right side, the superior intercostal vein drains into the azygos vein.
On the left side, show that this vein drains into the left brachiocephalic vein.
The superior intercostal veins drain two or three of the posterior intercostal veins; the rest of the posterior intercostal veins drain directly into larger veins.
The internal intercostal vein, which drains the anterior intercostal veins.

Detailed Diagram

We show the vertebral column and pelvis, with the ventral surfaces of the posterior thoracic cage (in other words, we’ve removed the ventral portion of the thoracic cage). We’ve numbered the intercostal spaces.

Superiorly, the brachiocephalic veins merge to form the superior vena cava; distally, the common iliac veins merge to form the inferior vena cava.
The iliolumbar veins drain into the common iliac veins; these veins drain the lumbar and sacral regions.
The ascending lumbar veins ascending along both sides of the vertebral column. The ascending lumbar veins form multiple venous channels to connect the veins of the lumbar and pelvic region with the azygos and hemiazygos veins; thus, they are important alternative routes if the inferior vena cava is blocked.
5 pairs of lumbar veins, as follows:

A fifth pair may drain into the iliolumbar veins, but this is variable. The 3rd and 4th pairs drain into the inferior vena cava, whereas the 1st and 2nd pairs drain into the ascending lumbar veins (but they may drain into the inferior vena cava, instead). The lumbar veins drain the lumbar segments of the spinal cord, back muscles and skin, and posterior abdominal wall.

The subcostal veins travel below the 12th ribs (“sub” means under or below; this vein is below the ribs).
On the right side, the subcostal and ascending lumbar veins drain into the azygos vein, which ascends along the posterior thoracic wall until it drains into the superior vena cava, at approximately T4 (drainage of the azygos vein into the brachiocephalic vein is a normal variant).
The azygos vein directly and indirectly receives blood from 10 of the 11 right-side posterior intercostal veins: veins 5-11 drain directly into the azygos vein, and veins 2, 3, and 4 merge to form the superior intercostal vein, which then drains into the azygos vein.
The azygos vein also receives blood from the pericardial, esophageal, and bronchial veins.
The first posterior intercostal vein is the anomaly: on both sides of the body, it drains directly into the brachiocephalic vein (alternatively, it may drain into the vertebral vein).
The posterior intercostal veins drain the posterior thoracic wall.
The internal thoracic vein drains into the brachiocephalic vein; this vein is an anterior thoracic wall vessel, but we’re showing it for context.
The subcostal and ascending lumbar veins drain into the hemiazygos vein, which ascends along the thoracic wall until approximately T8, where it crosses over the vertebral column and drains into the azygos vein.
Posterior intercostal veins 8-11 drain into the hemiazygos vein.
Posterior intercostal veins 4-7 drain into the accessory hemiazygos vein, which also crosses over the vertebral column to drain into the azygos vein at approximately level T7.
There may be a connection between the hemiazygos and accessory hemiazygos veins.
Posterior intercostal veins 2 and 3 merge to form left superior intercostal vein, which drains into the brachiocephalic vein.
The 1st posterior intercostal vein draining directly into the brachiocephalic vein.

Notes on the anterior thoracic wall:

The internal thoracic vein drains the anterior intercostal, musculophrenic, and superior epigastric veins; the inferior epigastric vein drains into the external iliac vein.

Veins - Trunk & Abdominal Walls

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