EP11.20: Prenatal diagnosis of Trisomy 21 and transient abnormal myelopoiesis

Hepatosplenomegaly diagnosed on prenatal ultrasound has several etiologies, the most common being intrauterine infection with the TORCH group of pathogens, and anemia. Rarer diagnoses of primary fetal tumours or myeloproliferative disorders are more difficult to diagnose prenatally but should be considered. We present the case of a 33-year-old woman with a fetus at 31 weeks gestation referred with hepatosplenomegaly (size and volume parameters >95th centile). The fetus also had hydrops; with ascites, placentomegaly, and pericardial effusion. The middle cerebral artery peak systolic velocity was greater than 1.5 MoM, consistent with fetal anemia. Amniocentesis was performed for QF-PCR, chromosomal microarray and viral studies. Antenatal corticosteroids were administered. The woman presented a day later with reduced fetal movements, and cardiotocography showed a sinister trace. The fetus was found to have Trisomy 21 on QF-PCR, and the likely diagnosis of transient abnormal myelopoiesis (TAM) was made. An emergency Caesarean section was performed as per the family’s wishes, with birth of a vigorous female at 31.3 weeks gestation. The initial Full Blood Picture and blood film showed a hemoglobin of 7.8g/dL, white cell count of 68 x 109/L, with CD61+ megakaryoblasts of 78 per cent, confirming likely TAM, or myeloid leukemia associated with Trisomy 21. The neonate was coagulopathic and thrombocytopenic at birth. Additional diagnoses were duodenal atresia and large patent ductus arteriosus. The neonate received blood products and chemotherapy with some improvement, but unfortunately succumbed to complications of prematurity and sepsis at day 26 of life. This case demonstrates the ultrasound features associated with the rare antenatal diagnosis of TAM, with fewer than 50 documented cases in the literature so far. When faced with this ultrasound sign, it is important to consider TAM in a fetus with Trisomy 21.