False diagnosis of renal agenesis on fetal MRI.

We report a twin pregnancy in which prenatal ultrasound revealed anhydramnios and bilateral absence of the kidneys in both fetuses. To overcome the difficulties faced in obtaining accurate information on fetal ultrasound in cases with oligohydramnios, an attempt was made to use fetal magnetic resonance imaging (MRI) to confirm the renal status. However, while the fetal MRI showed renal agenesis in both twins, postnatal follow-up revealed that one twin, which survived, had a small unilateral kidney not seen antenatally on fetal ultrasound or MRI. The second twin had bilateral renal agenesis and died of pulmonary hypoplasia. Care should be taken when using fetal MRI to replace fetal ultrasound in cases with poor visibility.