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Erythroblastosis in the peritoneal fluid of a newborn

A female newborn with hydrops fetalis was born by cesarean section at 29 weeks gestation with a birth weight of 1,290 g. Her mother, a recent Somali immigrant, had a history of multiple spontaneous abortions and intrauterine fetal demise due to anti-D antibodies. An abdominal tap of the newborn was performed and yielded 80 ml of orange-colored fluid. A Wright-stained cytospin preparation and a Papanicolaou-stained Surepath preparation were prepared from the peritoneal fluid and showed numerous erythroid precursors in all stages of maturation (Fig. C-1). Most erythroid cells were basophilic, polychromatic, and orthochromatic normoblasts (nucleated red blood cells) (Figs. C-2A–C), but occasional pronormoblasts were also seen (Fig. C-2D). Rare mesothelial cells and foamy histiocytes were also present, but no myeloid or megakaryocytic precursors were identified. The term ‘‘hydrops fetalis’’ denotes excessive fluid accumulation within the fetal extravascular compartments and body cavities (ascitis, pleural, or pericardial effusions) and can be caused by a wide variety of diseases. In the past, most cases of hydrops fetalis were due to Rh alloimmunization. After the introduction of routine immunization of Rhesus (Rh)-negative mothers, Rh alloimmunization causing erythroblastosis fetalis has become rare. At present, only about 4% of all cases of fetal hydrops in the United States are due to Rh alloimmunization. Most cases of hydrops fetalis are caused by nonimmune etiologies such as congenital heart disease, abnormalities in heart rate, hemoglobinopathies, and congenital malformations. Unfortunately, immunization of Rh-negative mothers is not routinely practiced in some parts of the world and Rh-alloimmunization caused by the transplacental passage of maternal anti-D antibodies active against paternally transmitted Rh(D) red blood cell antigens of the fetus may result in hemolytic anemia of variable severity. When mild, hemolytic disease of the newborn manifests only as mild anemia and reticulocytosis. In more severe forms, anemia is accompanied by erythroid hyperplasia and an increase in circulating nucleated red blood cells (erythroblastosis), reticulocytosis and, in very severe forms, by hydrops fetalis. The most severe forms result in spontaneous abortions or intrauterine death due to rapidly developing anemia and congestive heart failure. The peritoneal, pleural, and pericardial effusions found in neonates with erythroblastosis fetalis are caused by a combination of congestive heart failure due to anemia and decreased oncotic pressure. The decreased oncotic pressure is due to a reduction in serum albumin caused by hepatic dysfunction, which in turn is caused by hypoxia and massive hepatic extramedullary hematopoiesis. Hypoxia caused by severe hemolytic anemia activates the production of erythropoietin in the kidney resulting in the increased production of red blood cell precursors. Extramedullary hematopoiesis ensues after the hematopoietic capacity of the bone marrow is exhausted. Extramedullary hematopoiesis occurs predominantly in the liver and spleen, but can also occur in the peritoneum, pleura, or pericardium. In such cases, hematopoietic cells from the erythroid lineage may be found in cytologic preparations from effusions, as seen in the present case. The large number of erythroid precursors seen in the peritoneal fluid in this case rules out a potential contamination of the fluid with circulating nucleated red blood cells from the peripheral blood. Department of Laboratory Medicine and Pathology, University of Minnesota Medical School, Minneapolis, Minnesota *Correspondence to: Stefan E. Pambuccian, M.D., Professor, Department of Laboratory Medicine and Pathology, University of Minnesota Medical Center, Fairview, C422 Mayo MMC 76, 420 Delaware Street SE, Minneapolis MN 55455, USA. Tel.: +(612)-273-4934, (612)-2735920. Fax: +(612)-273-1142. E-mail: pambu001@umn.edu Received 3 October 2011; Accepted 19 November 2011 DOI 10.1002/dc.22823 Published online 1 February 2012 in Wiley Online Library (wileyonlinelibrary.com).