Prenatally diagnosed patent urachus with bladder prolapse.

We report 2 cases of patent urachus with bladder prolapse, which has a characteristic finding of "disappearance of cyst" antenatally. In the first case, a 34-year-old woman presented at 14 weeks gestation for evaluation of a cyst. Prenatal ultrasonography revealed a cystic mass at the base of the umbilical cord, communicating with the bladder. At 26 weeks gestation, the cyst had disappeared, and a solid mass bulged out inferior to the umbilical cord. At term, the patient delivered a male infant. Examination of the neonate demonstrated mucosal protrusion inferior to the umbilical cord. Catheterization confirmed communication with the bladder. We diagnosed patent urachus with bladder prolapse. In the second case, a 36-year-old woman presented at 19 weeks gestation for evaluation of moderate bilateral hydronephrosis and an abdominal cyst. Prenatal ultrasonography revealed a cystic mass at the base of the umbilical cord, communicating with the bladder. At 26 weeks gestation, the cyst had disappeared. At term, the patient delivered a male infant displaying patent urachus with bladder prolapse. Understanding of the development of urachus is important for prenatal diagnosis, which in turn allows surgery immediately after birth. We showed bladder function after surgery remains good at school age.