Hepatosplenomegaly Associated with Transient Abnormal Myelopoiesis in Down Syndrome: An Autopsy Case of a Stillborn Fetus

A 38-year-old primiparous mother (gravida 1, para 0) at 27 weeks and 6 days' gestation reported that fetal movements had been absent for 6 days. All serological markers for infection were negative. Chorionic villus sampling at stillbirth delivery revealed trisomy 21 (47, XX, +21), indicative of Down syndrome. The macerated baby was female and weighed 1,290 g. There was no evidence of hydrops fetalis. Proliferating blast cells expressing megakaryoblastic/megakaryocytic antigen CD61 were mainly seen within the vessels, and some cells infiltrated outside of the vessels in almost all organs. Vessels of the umbilical cord and chorionic villi were filled with proliferating blast cells, but the blast cells were not apparent in the bone marrow. The diagnosis of transient abnormal myelopoiesis in Down syndrome was made. Hepatomegaly (64.5 g) was due to congestion and infiltration of CD61-positive blast cells within the vascular lumina and expanding outside the lumina accompanied by fibrotic change. The cause of death was attributed to liver insufficiency caused by liver fibrosis. An umbilical cord and chorionic villi examination may be helpful in the diagnosis of transient abnormal myelopoiesis when post-mortem examination is not permitted