Blood finds a way: pictorial review of thoracic collateral vessels.

In the healthy patient, blood returns to the heart via classic venous pathways. Obstruction of any one of these pathways will result in blood flow finding new collateral pathways to return to the heart. Although significant anatomic variation exists and multiple collateral vessels are often present in the same patient, it is a general rule that the collateral pathways formed are a function of the site of venous blockage. Therefore, knowledge of typical collateral vessel systems can provide insight in localizing venous obstruction and characterizing its severity and chronicity. In addition, knowledge of collateral anatomy can be essential in interventional procedural and/or surgical planning, especially when placing catheters in patients with venous blockage. In this pictorial review, we provide a systematic approach to understanding collateral pathways in patients with venous obstruction in the upper body.