death during the critical developmental period (i.e., 1 month to 1 year). These vulnerability factors may be specific to the parents or the infant, whereas the exogenous stressor or stressors are attributable to the environment (
Table 7.7 ). Although numerous factors have been proposed to account for a vulnerable infant, the most compelling hypothesis is that SIDS reflects a delayed development of arousal and cardiorespiratory control. The brain stem and, in particular, the medulla oblongata play a critical role in the body’s “arousal” response to noxious stimuli such as episodic hypercarbia, hypoxia, and thermal stress encountered during sleep. The serotonergic (5-HT) system of the medulla is implicated in these “arousal” responses as well as regulation of other critical homeostatic functions such
Anatomicstudiesofvictimshaveyieldedinconsistenthistologicfindings.Multiple petechiae arethemostcommonfindinginthetypicalSIDSautopsy(inapproximately80%ofcases);theseusuallyarepresentonthethymus,visceralandparietalpleura,andepicardium.Thelungsusuallyarecongested,andvascularengorgementwithorwithoutpulmonary edema ispresentinamajorityofcases.Sophisticatedmorphometricstudieshaveshownquantitativebrainstemabnormalitiessuchashypoplasia of the arcuate nucleus orasubtledecreaseinbrainstemneuronalpopulationsinseveralcases;theseobservationsarenotuniform,however,andtheuseofsuchstudiesisnotfeasibleinmost“routine”autopsyprocedures.
•SIDSisadisorderofunknowncause,definedasthesuddendeathofaninfantyoungerthan1yearofagethatremainsunexplainedafterathoroughcaseinvestigationincludingperformanceofanautopsy.MostSIDSdeathsoccurbetweentheagesof2and4months.
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ThemostlikelybasisforSIDSisadelayeddevelopmentofarousalreflexesandcardiorespiratorycontrol.
Numerousenvironmentalriskfactorshavebeenproposed,ofwhichthepronesleepingpositionisbestrecognized—hencethesuccessofthe“BacktoSleep”programinreducingtheincidenceofSIDS.
Fetal hydrops refers to the accumulation of edema fluid in the fetus during intrauterine growth. The causes of fetal hydrops are manifold; the most important are listed in
Table 7.8 . In the past, hemolytic anemia caused by Rh blood group incompatibility between mother and fetus (immune hydrops) was the most common cause, but with the successful prophylaxis of this disorder during pregnancy, other causes of nonimmune hydrops have emerged as the principal culprits. The fluid accumulation can be quite variable, ranging in degree from progressive, generalized edema of the fetus (hydrops fetalis), a usually lethal condition, to more localized and less marked edematous processes, such as isolated pleural and peritoneal effusions or postnuchal fluid collections (cystic hygroma), that often are compatible with life (
Fig. 7.27 ). The mechanism of immune hydrops is discussed first, followed by other important causes of fetal hydrops.
Table 7.8 Major Causes of Fetal Hydrops
TurnersyndromeTrisomy21,trisomy18 *Thecauseoffetalhydropsmaybeundetermined(“idiopathic”)inupto20%ofcases.DatafromMachinGA:Hydrops,cystichygroma,hydrothorax,pericardialeffusions,andfetalascites.InGilbert-BarnessE,etal,editors:Potter’s pathology of the fetus, infant, and child, St.Louis,2007,Mosby,pp33.