Significance of paravertebral venous collaterals on excretory urography

The visualization of paravertebral venous collateral vessels during excretory urography may be normal when a foot vein has been injected. This finding reflects the abundant intercommunications between the caval, vertebral, and azygos venous systems and should not be mistaken for vena caval occlusion unless strong clinical suspicion of deep venous thrombosis exists.