Prenatal MR imaging features of Caroli syndrome in association with autosomal recessive polycystic kidney disease.

Caroli syndrome, which is characterized by saccular and fusiform dilatation of the biliary ducts, is usually observed in association with autosomal recessive polycystic kidney disease (ARPKD). Although the diagnosis of ARPKD is generally easy to make in postnatal ultrasound, the diagnosis of Caroli syndrome may be challenging in prenatal ultrasound. Herein, we present a case of a 29-week fetus with ARPKD associated with Caroli syndrome in whom fetal magnetic resonance imaging was essential to identify the "central dot sign" within the dilated biliary ducts to confirm the prenatal diagnosis of Caroli syndrome and to increase our level of confidence in this diagnosis.