Placenta
Umbilical cord
Amnionic web

Author: Paul J. Kowalski, M.D. (see Authors page)

Revised: 17 October 2017, last major update July 2015

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

PubMed Search: Amnionic web

Cite this page: Kowalski, P.J. Amnionic web. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/placentaamnioticweb.html. Accessed October 23rd, 2017.
Definition / general
  • Small portion of amniotic membrane can be present extending from the base of the umbilical cord and spanning the angle made by the fetal surface and the umbilical cord insertion
Terminology
  • Amnion is the single layer of cuboidal to columnar cells that lines the entire amniotic cavity, including the fetal surface of the placenta and the umbilical cord
  • Amniotic web should be distinguished from an amniotic band, which is a congenital amniotic malformation that can result in serious constriction or entrapment of fetal parts (amniotic band syndrome or amniotic rupture sequence)
Epidemiology
  • Uncommon finding, present in < 1% of uncomplicated live births
Pathophysiology
  • Amnion (and its underlying thin layer of amniotic mesoderm) is only loosely adherent to the adjacent chorion
  • This incompletely anchored nature of the amnion allows for incomplete investment of the acute angle made by the umbilical cord insertion and fetal surface
Clinical features
  • Generally an incidental finding with no clinical significance
  • Potential restriction of umbilical cord movement or constriction of vascular flow may be seen due to traction
Gross description
  • Translucent, delicate, sail-like portion of amnion spans the distance between a short segment of umbilical cord and the adjacent fetal surface
  • Retraction of the amnion can cause the umbilical cord to become tethered or anchored closely to the fetal surface
Gross images

Images hosted on other servers:
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Limited movement at the cord base

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Near term placenta

Differential diagnosis
  • Amniotic bands: consist of sheets or thicker strands / bands of amnion that can be found tethering any portion of the umbilical cord (not just its insertion site) or spanning between any portion of placenta and developing fetus