Perinatal visceral fibrosis accompanying the megakaryoblastic leukemoid reaction of Down syndrome.

Two infants with Down syndrome, one 4 weeks old and the other stillborn, at necropsy showed hepatic and pancreatic fibrosis, which was very severe in the liver of the liveborn infant and in the pancreas of the stillbirth. The liveborn infant had typical hematological features of the transient congenital leukemoid reaction of Down syndrome, and the identification of a megakaryoblastic component was consistent with recent opinion that this is a spontaneously-remitting congenital megakaryoblastic leukemia. The hydropic stillborn infant had intense extramedullary megakaryocytosis. The visceral fibrosis may have had a pathogenesis similar to that postulated for the myelofibrosis of megakaryoblastic leukemia in older children.