Fetal megakaryocytic dyshemopoiesis in Down syndrome: association with hepatic and pancreatic fibrosis.

Trisomy 21 was diagnosed by prenatal blood sampling at 30 and 31 weeks of gestation, respectively, in two fetuses with hepatosplenomegaly. In both, the fetal blood contained blast cells and cells showing megakaryocytic differentiation. Case 1 died neonatally 1 week later and the cellular infiltration causing enlargement of liver and spleen had a megakaryocytic/megakaryoblastic component staining positively for von Willebrand factor and binding to Ulex europaeus 1. Case 2, when stillborn 4 weeks later, had remarkably severe hepatic and pancreatic fibrosis. Cells in pulmonary vessels had morphology and immunohistochemical reactions consistent with megakaryocytic/megakaryoblastic differentiation. Comparison of the two cases suggests that the visceral fibrosis of perinatal Down syndrome may progress very rapidly in utero. They demonstrate further the association of the fibrosis with a dyshemopoiesis in which there is proliferation of cells of megakaryocytic lineage and a close relationship to the transient leukemia of neonatal Down syndrome.