Characteristic prenatal ultrasonographic findings of patent urachus: a case report.

A characteristic prenatal ultrasonographic finding of patent urachus is described. Routine obstetrical ultrasonography first revealed a cystic mass in the umbilical cord at 16 weeks of gestation. The mass spontaneously decreased in size and was undetectable at full term on serial ultrasound examination. The male newborn infant was delivered uneventfully at 38 weeks of gestation, weighing 2,774 g. He was noted to void urine from the umbilicus soon after birth, and the diagnosis of patent urachus was confirmed. On the 8th day of life, complete surgical removal of the urachus was performed, and the postoperative course was uneventful. An umbilical cystic mass which diminishes in size over the course of pregnancy is a sugesstive prenatal sonographic finding for urachal anomalies.