Superior vena cava obstruction: a venographic classification.

Analysis of venacavograms in 27 patients with superior vena caval obstruction revealed the following four patterns of venous collateral return: type I, partial obstruction (up to 90% stenosis) of the superior vena cava with patency of the azygos vein; type II, near-complete to complete obstruction (90-100%) of the superior vena cava with patency and antegrade flow through the azygos vein and into the right atrium; type III, near-complete to complete obstruction (90-100%) of the superior vena cava with reversal of azygos blood flow; type IV, complete obstruction of the superior vena cava and one or more of the major caval tributaries, including the azygos system. These patterns correlate well with the patients' clinical courses and can be used to identify patients who are at risk of developing cerebral and airway compromise and therefore would benefit from superior vena cava bypass surgery.