Extramedullary hematopoiesis in the allograft liver

The clinicopathologic correlates of extramedullary hematopoiesis were studied in 77 allograft biopsies from 27 patients who underwent liver transplantation for end-stage liver disease. The patient cohort consisted of 19 men and 8 women, ranging in age from 23 to 75 yr (median 41). The causes of end-stage liver disease included viral hepatitis (n = 20), ethanol abuse (n = 6), and congenital hepatic fibrosis (n = 1). Most patients (23 of 27) had significant septic complications in the postoperative period. The hematocrit was typically low (25 to 31%), and a history of allograft hepatectomy with retransplantation was available in 10 of 27 (37%) patients. Extramedullary hematopoiesis was first diagnosed 5 to 461 days (median 275) post-transplant and persisted 7 days to 36 mo (median 1 mo) thereafter. Pathologic findings concurrent with extramedullary hematopoiesis were acute cellular rejection/central venulitis (n = 7), ischemic preservation injury (n = 10), chronic rejection (n = 5), and chronic hepatitis/cirrhosis (n = 5). The pathogenesis of extramedullary hematopoiesis in these cases is not clear, but a low hematocrit may have been a stimulant for the observed hematopoiesis. In addition, the frequent coexistence of infectious, immunologic, or ischemic injury within the allograft suggests that reparative responses can stimulate intrahepatic stem cells to undergo hematopoietic differentiation. The cytokines likely involved in this process are discussed.