Background. Graft losses due to leaks, bleeding, thrombosis, infections, and early pancreatitis are grouped together under the category of technical failure. Among these complications, massive vascular thrombosis continues to be the most important cause of early graft loss due to technical failure. Pathological evaluation of most allografts lost early in the posttransplantation period shows vascular thrombosis with associated proportional parenchymal necrosis. The morphological findings in allografts that are considered to be lost due to technical failure has not been systematically addressed. In particular, the role of acute rejection in early graft loss has not been well studied. Methods. Seventy-four consecutive pancreas graft pancreatectomies were studied histologically to evaluate for thrombosis (recent versus organized), type of vessel involved by thrombosis (arteries, veins, or both), acute rejection grade, chronic rejection grade, endotheliitis, transplant arteritis, coagulation necrosis, acute pancreatitis, presence of infectious organisms, transplant (obliterative) arteriopathy, neoplasia, relative proportions of alpha and beta islet cells, and immunoglobulin and complement deposition. The histological findings were correlated with donor and recipient data as well as clinical presentation. Results. In 23 out of 39 grafts lost in the first 4 weeks posttransplantation, the only pathological changes found were vascular thrombosis and bland ischemic parenchymal necrosis. In these cases, no underlying vascular pathology or any other specific histological change was identified. Most of these grafts (78%) were lost in less than 48 hr and all in the first 2 weeks posttransplantation. Massive vascular thrombosis occurring in an otherwise histologically normal pancreas was the most common cause of graft loss in the first 4 weeks posttransplantation (59%). In most of the remaining cases (33%), although the clinical presentation suggested technical failure, there was clear histological evidence that the massive thrombosis resulted from vascular injury due to immune damage (acute and hyperacute rejection). Increased incidence of early graft thrombosis was seen in grafts from older donors and longer cold ischemia times. After the first month posttransplantation, graft pancreatectomies revealed a wider variety of pathological processes that included severe acute rejection, combined acute and chronic rejection, chronic rejection, and infections. Acute and chronic vascular thrombosis in large and small vessels was commonly seen at all times posttransplantation; chronic, organized thrombosis was strongly associated with chronic rejection. Conclusions. (a) Early acute thrombosis occurring in a histologically normal pancreas defines a true technical failure. This study showed that acute rejection leading to massive thrombosis, which clinically simulates technical failure, results in a significant proportion of early graft losses. (b) Systematic histological evaluation of failed grafts is absolutely necessary for the accurate classification of the cause of graft loss. (c) There is morphological evidence that chronically ongoing thrombosis is an important, common, contributing factor for late graft loss.
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