Congenital cystic adenomatoid malformation: a sheep model of fetal hydrops.

Congenital cystic adenomatoid malformation (CCAM) can be diagnosed in utero. Nonimmune hydrops associated with CCAM is a predictor of fetal demise. Fetuses with prenatally diagnosed large CCAM tumors and hydrops have undergone successful in utero resection. An animal model is needed to understand the pathophysiology of CCAM and hydrops. To create a model of CCAM and hydrops, the authors implanted an intrathoracic tissue expander in six fetal sheep at 120 days' gestation. The inflatable tissue expander was implanted in the right side of the chest, and arterial, venous, intrathoracic, and intraamniotic pressure catheters were placed. Each day, the expander was inflated with 25 to 50 mL of saline (maximum, 150 mL), ultrasound examination was performed, and all pressure measurements were taken. In all six fetuses, hydrops developed after expander inflation. Expander inflation correlated with an increase in central venous pressure (CVP) (4 +/- 2 mm Hg v 16 +/- 2 mm Hg [mean +/- SD]; P < .05). To simulate in utero CCAM resection, the expander was deflated in four hydropic sheep, resulting in return of the CVP to near baseline and resolution of hydrops. Silicone vascular casts of two postmortem sheep demonstrated lateral displacement and compression of the vena cavae by the expander. The authors successfully created a model of CCAM and hydrops by inflating an intrathoracic tissue expander in fetal sheep. Based on this model, hydrops associated with CCAM results from obstruction of cardiac venous return and central venous hypertension. This pathophysiology is reversed by expander deflation, which simulates in utero CCAM resection.(ABSTRACT TRUNCATED AT 250 WORDS)