Fig.7.27 ),andlesserdegreesofedemasuchasisolatedpleural,peritoneal,orpostnuchalfluidcollectionscanoccur.Accordingly,infantsmaybestillborn,diewithinthefirstfewdays,orrecovercompletely.Thepresenceofdysmorphicfeaturessuggestsunderlyingconstitutionalchromosomalabnormalities;postmortemexaminationmayshowacardiacanomaly.Inhydropsassociatedwithfetalanemia,bothfetusandplacentaarecharacteristicallypale;inmostcases,theliverandspleenareenlargedasaconsequenceofcardiac failure andcongestion.Additionally,thebonemarrowshowscompensatoryhyperplasiaoferythroidprecursors(parvovirus-associatedaplasticanemiabeinganotableexception),andextramedullary hematopoiesis ispresentintheliver,thespleen,andpossiblyinothertissuessuchasthekidneys,thelungs,thelymphnodes,andeventheheart(
Fig.7.29 ).Theincreasedhematopoieticactivityaccountsforthepresenceintheperipheralcirculationoflargenumbersofnormoblasts,andevenmoreimmatureerythroblasts(erythroblastosis fetalis).
ThepresenceofhemolysisinRhorABOincompatibilityisassociatedwiththeaddedcomplicationofincreasedcirculatingbilirubinfromtheredcellbreakdown.TheCNSmaybedamagedwhenhyperbilirubinemiaismarked(usuallygreaterthan20mg/dLinfull-terminfants,butoftenlessinprematureinfants).Thecirculatingunconjugatedbilirubinistakenupintothebrain,onwhichitapparentlyexertsatoxiceffect.Thebasalgangliaandbrainstemareparticularlypronetodepositionofbilirubinpigment,whichimpartsacharacteristicyellowhuetotheparenchyma(kernicterus) (
Fig.7.30
Early recognition of fetal hydrops is imperative, because even severe cases can sometimes be salvaged with timely therapy. Immune hydrops that results from Rh incompatibility can be predicted with reasonable certainty, because its severity correlates well with rapidly rising Rh antibody titers in the mother during pregnancy. Antenatal identification and management of the at-risk fetus have been facilitated by amniocentesis and the advent of chorionic villus and fetal blood sampling. The direct anti-globulin test (direct Coombs test) (Chapter 12) using fetal cord blood yields a positive result if the red cells have been coated by maternal antibody. In addition, cloning of the RHD gene has resulted in efforts to determine fetal Rh status by sequencing cell free DNA in maternal blood. When identified, cases of severe intrauterine hemolysis may be treated by fetal intravascular transfusions via the umbilical cord and early delivery. Postnatally, phototherapy is helpful, because visible light converts bilirubin to readily excreted dipyrroles. As already discussed, in an overwhelming majority of cases, administration of RhIg to the mother can prevent the occurrence of immune hydrops in subsequent pregnancies. Group ABO hemolytic disease is more difficult to predict but is readily anticipated by awareness of the blood incompatibility between mother and father and by hemoglobin and bilirubin determinations in the vulnerable newborn. In fatal cases of fetal hydrops, a thorough postmortem examination is imperative to determine the cause and to exclude a potentially recurring cause such as a chromosomal abnormality.
Fig. 7.29 Numerousislandsofextramedullaryhematopoiesis(small blue cells) arescatteredamongmaturehepatocytesinthishistologicpreparationfromaninfantwithnonimmunehydropsfetalis.