Disappearing fetal umbilical cord masses. Are these findings suggestive of urachal anomalies?

Ultrasonography is useful in the identification and evaluation of the fetus with an umbilical cord or abdominal wall abnormality. Recently, we reported the first case of the prenatal diagnosis of fetal patent urachus.1 We subsequently diagnosed a second fetus with patent urachus. To date, no other reports of the prenatal ultrasonographic appearance of patent urachus have been published. Early in embryological development (at approximately 16 days after conception), the allantois forms from a diverticulum off the yolk sac. As the embryo grows, the allantois becomes incorporated into the abdomen of the fetus to form a hollow tube that connects the superior aspect of the urogenital sinus (the apex of the bladder) with the anteripr abdominal wall at the umbilicus. Eventually, the lumen of this tube becomes obliterated, resulting in a thick fibromuscular cord that connects the bladder with the umbilicus. This cord is the urachus, which has no apparent function after the first few weeks of development. A cessation of the luminal obliteration will occur rarely. The resulting abnormality may be one of several similar malformations including patent urachus (complete luminal patency), urachal diverticulum (patency of only the proximal urachus), urachal sinus (patency of only the distal urachus), or a urachal cyst (patency of only the medial urachus).