It develops when the blood vessels and stroma undergo rapid proliferation independent of the surrounding tissue.

Chorioangioma is seen as a hypo- or hyperechoic circumscribed mass that is distinct from the placenta at gray-scale US examination.

Doppler examination shows anechoic cystic areas, with pulsatile flow in spectral analysis.

In case of maternal or foetal complications, possible interventions are serial foetal transfusions, fetoscopic laser coagulation of vessels supplying the tumor, endoscopic surgical devascularization and chemosclerosis using absolute alcohol.

When chorioangiomas have deceased blood flow, fetal hemodynamics and clinical outcome are found to be improved.

Chorioangiomas over the size of 5 cm in diameter are rare, and occur at a rate of 1:3500 to 1:16,000 births.