The allantois forms from the part of the fetal
yolk sac that eventually becomes the primitive hindgut (the cloaca).
The cloaca divides into the hindgut posteriorly and the urogenital
sinus anteriorly. The allantois
remains connected to the urogenital sinus and extends
into the base of the umbilical cord.
The umbilical cord is formed from the fusion of the body stalk (containing
the allantois) and the umbilical vessels and yolk
stalk (containing the omphalomesenteric duct) (1).
The allantois usually regresses by 14 menstrual
weeks, but may occasionally persist and present as a cystic mass in the base of
the umbilical cord (2).
- Anechoic cystic mass of the
- Centrally located in the
cord with the umbilical vessels located against the outer wall.
- Located at the fetal end of
the umbilical cord.
- Size ranges from 5 mm to 5
- May / may not communicate
with the fetal bladder (5-7).
- May be demonstrated as
early as 9 menstrual weeks and may:
- Decrease in size.
- Persist throughout
the pregnancy (3).
- Urinary tract anomalies (especially
bladder outlet obstruction) in 18% of cases (8).
- Patent urachus
- Moore KL. The developing human. Second
WB Saunders 1977;51, 61-62, 112-113, 205-209.
- Romero R, Pilu G, Jeanty P et.al. Prenatal diagnosis of congenital abnormalities.
Appleton and Lange 1988;391-397.
AR. Sonographic first-trimester diagnosis of umbilical cord cyst. J Clin Ultrasound 1989;17:53-55.
- Sachs L, Fourcroy JL, Wenzel DJ et.al.
Prenatal detection of umbilical cord allantoic
cyst. Radiology 1982;145:445-446.
- Hughes HA, Feinstein SJ, Lodeiro JG et.al. Umbilical
cord cyst presenting as an omphalocele at 15
weeks gestation: a case report. J Reprod Med
MT, Templeton JM et.al. Prenatal sonographic diagnosis of a vesico-allantoic abdominal wall defect. J Ultrasound
- Harp J, Rouse GA,
De Lange M. Sonographic prenatal diagnosis of an allantoic
cyst. JDMS 1992;8:28-32.
WP. Patent urachus. South Med J 1937;30:711-719.
- Fink IJ, Filly RA. Omphalocele associated with umbilical cord allantoic cyst: sonographic evaluation in utero.
S -J, Lee Y -H, Joo MS et.al.
Unusual fate of vesicoallantoic cyst with
non-visualization of the fetal bladder in a case of patent urachus. Ultrasound Obstet Gynecol 1997;9:422-424.