Background
Hydrops fetalis (HF), also known as congenital edema or fetal anasarca, is not a diagnosis itself, but a syndrome that can accompany many diseases. The term refers to an excessive accumulation of fetal fluid in body cavities (abdominal and/or pleural cavity and/or pericardial sac) and subcutaneous edema. This congenital condition has been described both in the veterinary and human medical literature. It has been reported in cows, sheep , goat, cats and dogs. In dogs, this syndrome is also referred to as swollen puppies, water puppies or walrus puppies. English and French Bulldogs, Pugs, Pekingese, and Boston Terriers are considered as predisposed breeds, however the syndrome has also been reported in a Briard-Beagle crossbred dog and a Flat-coated Retriever [12]. HF may develop in one or more fetuses in the litter and can cause obstructive dystocia. Most of affected puppies die, usually shortly after birth. In human medicine, HF may be either immune-mediated or non-immune syndrome.
The former had been mostly caused by Rhesus isoimmunization, however, effective prophylaxis led to a substantial decrease in its incidence. Currently, it is estimated that non-immune HF accounts for up to 90% of all reported cases. Recent studies on human fetuses with HF have revealed the following causes: heart disease (15.2%) including cardiomyopathy, Ebstein’s anomaly, pulmonary valve stenosis, coarctation of aorta, aortic valvular stenosis, hypoplastic left heart, atrioventricular canal defect syndrome, mitral valve insufficiency, pulmonary artery anomaly, pulmonary artery atresia, double outlet right ventricle, single ventricle, myocarditis, tetralogy of Fallot, truncus arteriosus, coronary artery fistula, hypoplastic right heart, total anomalous pulmonary venous return, tricuspid valve atresia, aortic malformations, interrupted aortic arch, transposition of the great vessels (TGA), genetic causes (12.5%), arrhythmias (8.2%), infectious diseases of the fetus (7.6%), congenital anemia (5.2%), hemolytic anemia (3.8%), and twin-to-twin transfusion syndrome (3.8%). In nearly 30% of cases, the cause remains unknown. HF in humans may also be caused by heart tumors of the fetus. In the presence of pathological masses in the heart,
HF occurs due to impaired blood flow. The most commonly diagnosed heart tumor is rhabdomyoma and much less common fibroma, teratoma, and hemangioma. Based on very limited data from veterinary medicine cardiac malformations appear to be the most common cause of HF, but little data is available in animals. Both in humans and animals, HF can be diagnosed in the prenatal ultrasound.