Transient Abnormal Myelopoiesis with Myeloid Cell Thrombus in a Case of Down Syndrome: A Rare Placental Finding

This study was aimed to underscore the value of placental examination in identifying transient abnormal myelopoiesis (TAM), particularly in neonates with previously unsuspected Down syndrome (DS), and to demonstrate how such placental findings can guide timely clinical diagnosis when there is no antenatal suspicion.

This short communication describes the clinical, hematological, and placental pathological findings in a neonate born without prior antenatal suspicion of DS. Particular emphasis is placed on the identification of TAM and associated myeloid cell thrombus (MCT) within the placenta and their relevance in prompting further clinical evaluation.

The placental weight and dimensions were 330 g and 13 cm × 12 cm, and the disc was unremarkable on macroscopic examination. The umbilical cord showed thrombus in one of the vessels. On microscopy, the muscularized placental fetal vessels showed evidence of leukocytosis with left shift of hematopoietic elements inclusive of blast forms. Many nucleated red blood cells along with platelets and fibrin were also noted. These hematopoietic precursors were seen forming organized thrombi causing segmental high-grade lesions of fetal vascular malperfusion. The umbilical artery in the umbilical cord showed MCT (positive for CD 34 and CD 117 on immunohistochemistry). Hematological investigations with flow cytometry assisted in diagnosis, which was confirmed by genetic testing.

In situations where DS is not clinically suspected antenatally, recognition of TAM-especially when accompanied by MCT-on placental examination may serve as the first and only clue prompting clinicians to investigate for DS. This case underscores the pivotal role of placental pathology in facilitating early detection and appropriate management of such neonates.

· Placental transient abnormal myelopoiesis in an unsuspected case of Down syndrome.. · Myeloid cell thrombus in placental and umbilical cord vessels.. · Flowcytometry along with genetic testing, confirming diagnosis of Transient abnormal myelopoiesis and Down syndrome..