Obliterative phlebitis in a retroperitoneal mass from a patient with IgG4-related disease

Elastin stain of a retroperitoneal biopsy from a patient with classic retroperitoneal fibrosis. The arteries and veins course in proximity to each other at most anatomic sites, including in the retroperitoneum. This elastin stain shows normal, orderly staining of the internal elastic lamina of the thick-walled artery. By contrast, the elastin within the wall of the vein (situated just above the artery in this picture) is highly disorganized, and the lumen of the vessel can no longer be visualized. The vein has been destroyed (obliterated) by the inflammatory process.