umbilical cord cyst
description
there are several potential sources for an umbilical cord cyst. the allantois is an out-pouching of the yolk sac that is continuous with the urinary bladder. in reptiles and birds, urine is stored in the allantois during embryonic life. in the human the allantois becomes the urachus and begins to close at 7.4 menstrual weeks. when the communication between the fetal urinary bladder and allantois persists, a dumb-bell shaped vesico-allantoic cyst results. an allantoic cyst is isolated to the umbilical cord and does not communicate with the fetal bladder. if an umbilical cord cyst near the fetal abdominal wall decreases in size with advancing gestation, a urachal anomaly should be considered. an additional sonographic clue of an allantoic cyst is a diffuse enlargement of the umbilical cord distal to the cyst. dilatation of allantoic remnants has been found in the umbilical cord until 14 weeks’ menstrual age. battaglia and co-workers have reported a case of an expanding allantoic cyst that resulted in sufficient cord compression to produce fetal distress. omphaloceles are associated with allantoic cysts.
diagnosis
the omphalomesenteric duct connects the primitive mid-gut to the extra-embryonic yolk sac. it is eccentrically located within the umbilical cord and closes by 8 weeks’ menstrual age. cysts of the omphalomesenteric duct are, therefore, eccentrically positioned. they vary in size from 0.5 to 6.0 cm and occur more frequently on the fetal end of the umbilical cord. with the larger umbilical cord cysts, sonography cannot distinguish an omphalomesenteric cyst from the more common allantoic cyst. while omphalomesenteric duct cysts are usually lined with mucin-secreting epithelium, gastric, small intestinal and colonic epithelium may also be present. in a prospective study of 859 women between 7-13 weeks’ gestation, umbilical cord cysts were detected with transvaginal sonography in 29 (3.4%) viable pregnancies. 85% of the cord cysts resolved by 12 weeks’ gestation. in the latter group 3 of 23 fetuses (13%) had a structural malformation; none of the fetuses were karyotypically abnormal. although this series is small, it suggests that karyotyping may not be necessary for transient first trimester umbilical cord cysts. however, a detailed second trimester ultrasound examination is indicated to look for possible structural malformations.
differential diagnosis
umbilical cord cysts are usually confused with subchorionic septal cysts. an evaluation of the relationship between the umbilical cord and the cyst should help to distinguish between these two entities.
sonographic features
wharton’s jelly surrounds the umbilical vessels and functions as a supportive structure. it is not uncommon to find degenerative areas within wharton’s jelly. occasionally, these areas are so pronounced that they coalesce to form a cystic space
since a ”cyst” within wharton’s jelly does not have an epithelial lining, like allantoic or omphalomesenteric cysts, they are considered ”pseudocysts”. if a pseudocyst becomes large enough, it may also compress the umbilical vessels. antenatal sonography cannot differentiate between true cysts and pseudocysts.
sepulveda et al reported 2 cases of umbilical cord pseudocyst and reviewed 11 additional cases from the literature. the gestational age range for these 13 cases was 21-38 weeks. 7 of the 13 cases were associated with a karyotypic abnormality – trisomy 18 in 6 and trisomy 13 in 1.
second trimester umbilical cord cysts should, therefore, be considered an additional anomaly associated with trisomy 18.