The urachus is a vestigial remnant of embryonic life. It extends from the apex of the bladder toward the umbilicus. In the fetus the urachus is a hollow tube which attaches the bladder to the allantoic stalk. At birth the urachus descends with the bladder and comes to lie in the midline directly over the apex of the bladder. The two umbilical arteries become obliterated and are drawn together and drawn down in the midline, forming a continuous band, the ligamentum commune, which passes from the umbilicus to the apex of the urachus. In adult life the urachus extends from the apex of the bladder to a point approximately one-third of the distance to the umbilicus, and above this point the ligamentum commune continues as a midline structure.
The urachus is occasionally the source of neoplastic disease. It is lined with transitional epithelium and may give rise to carcinoma. The
BUTLER DB, ROSENBERG HS. Sarcoma of the Urachus. AMA Arch Surg. 1959;79(5):724-728. doi:10.1001/archsurg.1959.04320110026004