The internal thoracic vein forms from the venae commitantes which surround the internal thoracic artery during its passage through the thorax. At about the level of the third costal cartilage, the venae commitantes merge into a single vessel on each side that passes superiorly and medial to the artery.
Each internal thoracic vein drains into its respective brachiocephalic vein.
The internal thoracic vein on each side has tributaries:
- accompanying the internal thoracic artery branches to each intercostal space
- accompanying the phrenic nerve and pericardiophrenic artery through the thorax