Sirenomelia sequence versus renal agenesis: prenatal differentiation with power Doppler ultrasound.

In order to assess the role of power Doppler ultrasound in the prenatal diagnosis of sirenomelia, prenatal findings in two fetuses with the sirenomelia sequence and in seven with bilateral renal agenesis were reviewed and compared. Both conditions were characterized by absence of renal vessels. However, the two common iliac arteries were always visualized in fetuses with renal agenesis, whereas absence of distal branching of the main abdominal vessel was a characteristic feature of sirenomelia. Power Doppler ultrasound allows expeditious identification of absent or non-functional renal arteries in fetuses with severe oligohydramnios. In addition, incorporation of power Doppler imaging to identify the aortic bifurcation could provide a diagnostic feature that could assist in the prenatal diagnosis of sirenomelia and in the differential diagnosis with other causes of bilateral renal agenesis.