The contribution of extramedullary hematopoiesis to hepatomegaly in anemic hydrops fetalis: a study in alpha-thalassemia hydrops fetalis

Fetal Hepatomegaly: Causes and Associations

Fetal hepatomegaly is associated with significant fetal morbidity and mortality. However, hepatomegaly might be overlooked when numerous other fetal anomalies are present, or it might not be noticed when it is an isolated entity. As the largest solid organ in the abdomen, the liver can be seen well with US or MRI, and the normal imaging characteristics are well described. The length of the fetal liver, which can be used to identify hepatomegaly, can be determined by measuring the liver from the diaphragm to the tip of the right lobe in the sagittal plane. Fetal hepatomegaly is seen with infection, transient abnormal myelopoiesis, liver storage and deposition diseases, some syndromes, large liver tumors, biliary atresia, and anemia. Some of these diagnoses are treatable during the fetal period. Attention to the associated findings and specific hepatic and nonhepatic imaging characteristics can help facilitate more accurate diagnoses and appropriate patient counseling.^©RSNA, 2020.

Pulmonary Neuroendocrine Cell Hyperplasia in Hemoglobin Bart-induced Hydrops Fetalis: A model for Chronic Intrauterine Hypoxia

The pulmonary neuroendocrine system includes pulmonary neuroendocrine cells (PNECs) and neuroepithelial bodies (NEBs) that are distributed throughout respiratory epithelium and regulate lung growth and maturation antenatally. Abnormalities in this system have been linked to many hypoxia-associated pediatric pulmonary disorders. Hemoglobin (Hb) Bart disease is a severe form of α-thalassemia resulting in marked intrauterine hypoxia with hydrops fetalis (HF) and usually death in utero. Affected fetuses can serve as a naturally occurring human model for the effects of intrauterine hypoxia, and we postulated that these effects should include changes in the pulmonary neuroendocrine system. Bombesin immunostaining was used to assess PNECs and NEBs in stillborn fetuses with Hb Bart HF ( n = 16) and with HF from other causes ( n = 14) in comparison to non-HF controls. Hb Bart HF showed a significant increase in the proportion of PNECs in respiratory epithelium ( P = .002), mean number of NEB nuclei ( P = .03), and mean size of NEBs ( P = .002), compared to normal non-HF controls. Significant differences were not observed between HF due to other causes and non-HF controls with normal lungs. Non-HF controls with pulmonary hypoplasia showed significant increases in PNECs compared to HF cases not due to Hb Bart HF, implying HF alone does not cause such increases. In contrast, no significant differences were noted between non-HF controls with pulmonary hypoplasia and Hb Bart cases. Hb Bart HF may provide a useful model for studying the pulmonary neuroendocrine system under chronic intrauterine hypoxia.

Hemoglobin Bart hydrops fetalis: A model for studying vascular changes in placental hypoxia

INTRODUCTION

Placental ischemia can be pre-placental (maternal), placental or post-placental (fetal), with corresponding changes in villous vasculature. Hydrops fetalis (HF) resulting from hemoglobin (Hb) Bart disease can serve as a model for intrauterine hypoxia, and placentas from such cases show a distinctive peripheral villous stromal myofibroblastic hypercellularity (PVSH). We hypothesized that Hb Bart disease, which results in profound fetal hypoxia, would lead to placental hypoxia on a post-placental basis.

METHODS

We assessed villous vasculature using computerized morphometry, comparing placentas in 14 Hb Bart HF cases to 18 non-Hb Bart HF cases. Morphometric parameters were matched as closely as possible to those reported in the literature for comparison purposes.

RESULTS

Villous vessels of Hb Bart HF showed significantly increased numbers of vessels (p = 0.001), longer vascular perimeter (p = 0.002), thickening of vascular endothelial layer (p = 0.038) and higher shape coefficient (p = 0.042) indicating a more branching pattern of vessels. In addition, placental villi of Hb Bart HF containing PVSH showed a longer vascular perimeter (p = 0.008) and narrower lumen (p = 0.002), with a higher shape coefficient (p = 0.03), in comparison to villi lacking PVSH.

DISCUSSION

Contrary to expectations, the overall pattern of vascular changes in Hb Bart HF suggested multifactorial hypoxia: pre-placental, on the basis of the marked placentomegaly, compromising blood flow from uterine distention; placental, from hydropic villi causing a generalized diminished intervillous space; and post-placental from the greatly reduced capacity of Hb Bart to extract oxygen from the intervillous space. Standardized vascular morphometry will facilitate comparison between different conditions, for a better understanding of placental hypoxia.