Prenatal and Postnatal Clinical Course of an Urachus Identified as an Allantoic Cyst in the Umbilical Cord.

Purpose  The aim of this study was to clarify the prenatal and postnatal clinical courses of an urachus identified as an allantoic cyst in the umbilical cord. Methods  Allantoic cysts in the umbilical cord were identified in five fetuses over the past 12 years at our hospital. The prenatal and postnatal clinical courses of these patients were retrospectively reviewed. Results  The presence of allantoic cysts in the umbilical cord was first detected at 15 to 27 weeks of gestation. The cysts subsequently became enlarged, reaching a maximum diameter of 34 to 61 mm at 17 to 32 weeks of gestation. The cysts then suddenly disappeared due to spontaneous rupture at 26 to 35 weeks of gestation. After being born at 38 (35–39) weeks of gestation, four patients were diagnosed with a patent urachus requiring surgery in the infantile period and one was diagnosed with an urachal cyst, which is currently being observed without surgery. Conclusion  The presence of an urachus identified as an allantoic cyst in the umbilical cord is frequently associated with spontaneous rupture during the prenatal period, resulting in a patent urachus after birth that requires surgical intervention.