Allantoic Cyst Prior to Transient Megacystis in Patent Urachus: A Paradoxal Association?

Abstract

Patent urachus is a rare umbilical anomaly with an incidence of 1 to 2.5 per 100,000 deliveries. The urachus is a thin fibromusculartubular structure that represents the intra-abdominal portion of allantois extending from umbilicus to the vertex of the bladder. Under normal conditions, the urachus is not seen in utero, since the obliteration of its lumen usually occurs at six weeks of gestational age. An anomaly in allantois involution can result in patent urachus, umbilical urachal sinus, vesicourachal diverticulum, urachal cyst, or alternating sinus and should always be included in the differential diagnosis of midabdominal cysts. Before the advent of prenatal sonography, this condition was always diagnosed in early neonatal period. The authors report a rare case of a patent urachus suspected in the first trimester ultrasound.