Azygous and Hemi-Azygous

The azygous and hemi-azygous systems are the major routes for diversion of blood flow. These dilated vessels often widen the mediastinum on CXR and can be mistakenly interpreted to represent mass lesions.

When the obstruction is above the azygous vein, this major axillary channel takes over the function of the SVC.

When the obstruction occurs below the azygous arch or includes it, the patient tolerates this with far more difficulty. The venous pressure is much higher and the immediate prognosis more serious. The route of venous blood flow is now much more circuitous and complex and involves the support of the inferior vena cava.
SVC
SVC
SVC
SVC