The posterior intercostal arteries are paired vessels running in each intercostal space. The first and second arise from the superior intercostal artery (from the costocervical trunk), and the third through eleventh arise directly from the descending thoracic aorta. Each runs forward along the inferior border of the rib in the subcostal groove, protected by the rib above, giving rise to a collateral branch and then continuing anteriorly to anastomose with the anterior intercostal arteries from the internal thoracic artery.
The neurovascular bundle (artery, vein, and nerve) runs in the subcostal groove at the inferior margin of each rib in the order vein-artery-nerve from superior to inferior. Pleural aspiration, intercostal nerve block, and chest drain insertion must be performed at the superior margin of the rib below the target space to avoid the neurovascular bundle. The posterior intercostal arteries contribute spinal branches to the anterior spinal artery at each level; sacrifice of the arteries of Adamkiewicz level during aortic surgery causes spinal cord ischaemia.
Needle insertion or drain placement at the inferior margin of an intercostal space lacerates the posterior intercostal artery, causing haemothorax; all thoracic procedures requiring rib crossing should be performed over the superior border of the lower rib to avoid the neurovascular bundle in the subcostal groove.
Ligation of posterior intercostal arteries during thoracic surgery or aortic repair can sacrifice spinal medullary branches supplying the anterior spinal artery, causing spinal cord ischaemia if the artery of Adamkiewicz is inadvertently included; preoperative CT angiography identifies the level requiring protection.
