Placenta
Umbilical cord
Embryonic remnants

Reviewer: Paul J. Kowalski, M.D. (see Reviewers page)

Revised: 17 October 2017, last major update August 2015

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Embryonic remnants placenta
Cite this page: Kowalski, P.J. Embryonic remnants. PathologyOutlines.com website. http://pathologyoutlines.com/topic/placentaembryonicremn.html. Accessed November 22nd, 2017.
Definition / general
  • Vestigial structures representing extraembryonic ductal connections (the allantoic duct and the omphalomesenteric duct) in the primitive connecting (umbilical) stalk can be commonly seen in term placentas
Terminology
  • Yolk sac is an early embryonic structure, a portion of which will eventually be incorporated into the gut of the embryo; vitelline vessels supply the yolk sac and constitute the vitelline circulation
  • Allantois is the primitive extraembryonic urinary bladder and will eventually become the urachus, which connects the fetal bladder to the yolk sac; the allantoic duct originates as an outpouching of the yolk sac
  • Omphalomesenteric (vitelline) duct connects the midgut lumen with the yolk sac in the developing fetus
  • See diagram below
Epidemiology
  • Allantoic duct remnant is present in the proximal portion of 15% of umbilical cords
  • Omphalomesenteric duct remnant is present in about 1.5% of umbilical cords, often associated with remnants of vitelline vessels, seen in about 7% of umbilical cords
Pathophysiology / etiology
  • Allantoic duct usually regresses and is completely obliterated by 15 weeks gestation
    • Its persistence in the umbilical cord is common
    • Remnant (of the allantoic duct) between the umbilicus and the fetal urinary bladder persists as the medial umbilical ligament
  • Omphalomesenteric duct usually obliterates between 9 - 16 weeks gestation following gut rotation but can alternatively persist in term placentas
Diagrams / tables

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Clinical features
  • For allantoic duct remnants, usually no clinical significance
    • Rare cases of patent duct remnants can show urinary leakage from a clamped umbilical stump or cysts that may persist into adulthood
  • For omphalomesenteric duct remnants, usually no clinical significance
    • Rare cases of patent duct remnants can be symptomatic if direct communication is maintained with the fetal bowel or if ectopic gastric, pancreatic or intestinal mucosa stimulates tissue responses
    • Omphalomesenteric duct remnants have also been associated with intestinal atresia, Meckel diverticulum or intestinal protrusion into the umbilical cord through the duct
Case reports
Gross description
  • Typically no gross findings are evident (unless a rare cyst is present)
Microscopic (histologic) description
  • Allantoic duct remnants are usually located between the umbilical arteries of the proximal portion of the umbilical cord and are rarely accompanied by smooth muscle
    • Epithelium of the duct is cuboidal to flat and generally is of transitional type although mucin producing epithelium can be found
    • Small vessels around the periphery of the duct remnant may be occasionally seen
  • Omphalomesenteric duct remnants are also more common in the proximal umbilical cord but are present at the cord periphery and often have a smooth muscle wall
    • Epithelium of the duct is cuboidal to columnar with an intestinal phenotype
    • Rarely, mucosa resembling liver, pancreas, stomach or small intestine can be seen
    • Frequently, paired or clustered vitelline vessels (without muscular walls) will be associated with duct remnants
Microscopic (histologic) images

Images hosted on other servers:
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Allantoic duct remnant

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Omphalomesenteric duct remnant