Intravascular papillary endothelial hyperplasia in a thrombosed renal allograft vein.

Intravascular papillary endothelial hyperplasia (IPEH) is a benign endothelial proliferation of unclear pathogenesis, usually associated with thrombus as an unusual mode of organization and occasionally coexisting with vascular neoplasms. A 65-year-old white woman with chronic renal disease caused by focal segmental glomerulosclerosis experienced the failure of a cadaveric renal allograft 10 days after implantation. Pathological manifestations in the resected graft included total infarction and thrombi in both the renal artery and vein, the latter of which showed typical histopathologic features of IPEH. Papillary formations with fibrinous cores lined by bland endothelial cells surrounded fresh and organizing thrombus, and the proliferation had a highly cellular peripheral zone not readily recognizable as vascular. Immunohistochemical stains for factor VIII, CD34, and in particular CD31, however, confirmed the nature of both the papillary and solid areas of the proliferation as vascular endothelium. We present the first report of this lesion in an allograft vessel, and we find its rapid development, in association with a thrombus of clinically discernable age, to be strong evidence supporting the hypothesis that IPEH represents an uncommon morphology of organizing thrombus.