Morphologic features of chronic rejection in kidney and less commonly transplanted organs

Chronic rejection is characterized by morphological evidence of destruction of the transplanted organ. The injury to the organ is associated with collagenization of variable degree. The destruction and fibrosis of the organ is probably the result of 1) direct alloimmune cytotoxic injury (i.e., acute and/or ongoing rejection) of the organ tissue, and 2) end-organ ischemic injury secondary to fibroproliferative endarteritis (i.e., chronic vascular rejection). The cardinal morphological feature of chronic rejection in all allografts is fibroproliferative endarteritis, which is characterized by widening of the subendothelial space due to a cellular fibrosis which may have an onion-skin appearance with a PAS or silver stain. Macrophages with foamy cytoplasm and lymphocytes may be present in this fibrotic tissue. The smooth muscle wall may show foci of fibrosis as well, if involved by previous necrotizing rejection. These features are commonly found in needle core biopsies of kidney allografts and may involve the interlobular, arcuate, and interlobar arteries. They are less commonly found in pancreatic needle biopsies, and only rarely in hepatic and pulmonary allograft biopsies, rendering the diagnosis of chronic rejection often difficult to establish. Though the vascular lesions may not be apparent in biopsies, they are typically found in explanted organs where larger vessels can be examined. Thus, the diagnosis of chronic rejection may rest upon other and in some instances less specific abnormalities, usually ischemic in origin due to vascular lesions and consequent decreased perfusion of the graft.(ABSTRACT TRUNCATED AT 250 WORDS)