In this prospective multicenter study, we conclude that hydropic CDH is rare, only 2.8% of all prenatally diagnosed cases, and more commonly occurring in right sided CDH. Survival rates are low, with higher rates of non-repair. Hydrops is a clinical entity characterized by the presence of skin and scalp edema or fluid in two or more body compartments. In cases of fetal thoracic anomalies, such as CDH, it is thought to be caused by obstruction of venous return to the heart leading to elevated systemic venous pressures.
When using the term ‘hydrops’ in CDH, effusions in the thoracic cavity and abdominal cavity concomitant to the side of the defect, should be considered as one compartment for obvious reasons, avoiding confusion. Thus, true hydrops in CDH should refer to patients with excess fluid in at least two non-concomitant compartments.
However, the presence of excess of fluid in only one compartment is associated with worse outcome. Even if the association is rare, nearly 3% of all prenatally diagnosed CDH will present with fluid in 1 compartment, the survival rates are low (47.3%, Table 3). True hydropic CDH is even more rare, only identified in 0.35% of the prenatally diagnosed CDH cases, and more commonly occurring in right sided CDH. Survival rates for true hydropic CDH are very low: 78% of patients with true hydrops will not survive to discharge.
Malformations are present in half of the CDH with fluid / edema, true hydrops (fluid in at least two compartments) or non-true hydrops (fluid in 1 compartment), and more common among those who died before discharge (56% vs 42%, Table 2).
Skin edema seems to be an independent risk factor for worse outcome, with higher mortality. However, even though the pathophysiological mechanisms underlying this event remain unknown, an increased central venous pressure and/or obstructed lymphatic drainage may be the most plausible explanations. [refs]
Although the pathogenesis of hydrops in fetuses with CDH is poorly understood, right-sided lesions seem to be more likely to cause hydrops in CDH. Most of the cases presented here were right sided and/or had a major portion of the liver in the chest, thus the pathophysiology may be similar to other intrathoracic lesions, with mediastinal obstruction from solid organ herniation obstructing blood return to the heart. Since there is a confined space within the thorax, the herniation of a solid organ such as the liver, leaving a smaller portion intraabdominally, may lead to kinking and obstruction of the inferior vena cava, portal or hepatic vein.
Despite hydrops being more commonly associated with right sided CDH, in as many as half of the patients with hydrops have a right sided defect, left sided CDH has a poorer outcome, with higher rates of associated anomalies, high rates of non-repairs and is overrepresented among children who died before discharge (75% of the left sided CDH with hydrops will demise, probably due to the complexity of the CDH).
Even if the rates of non-repairs are high, a more aggressive surgical approach leads to acceptable survival rates: 80% of the patients being repair will survive to discharge. ECLS support is offered to the same extent to patients who survive and those hydrops patients who died before discharge.
In conclusion, the association of CDH and hydrops in the fetus is rare and the sole presence of excess fluid or edema in 1 compartment is associated with poorer outcome. The combination is associated with the presence of other associated anomalies and right-sided defects with liver involvement. Special attention should be given to the presence of skin edema resulting in higher mortality rates. An initially aggressive surgical approach may result in acceptable survival rates comparable to non-hydropic cases. Early decision-making regarding the aims of care clearly influence outcome, since survival varies depending on the severity of the CDH and the presence of other associated anomalies.