Nonneoplastic placental conditions and abnormalities


Amnion nodosum

Editorial Board Member: Ricardo R. Lastra, M.D.
Deputy Editor-in-Chief: Jennifer A. Bennett, M.D.
Caroline Simon, M.D.

Last author update: 13 October 2022
Last staff update: 13 October 2022

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PubMed Search: Amnion nodosum

Caroline Simon, M.D.
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Cite this page: Simon C. Amnion nodosum. website. Accessed July 13th, 2024.
Definition / general
  • Nodules of fetal skin, hair and fat found on the amnion
Essential features
  • Deposition of fetal squames as nodules of surface of amnion
  • Associated with severe prolonged oligohydramnios, anhydramnios
  • Vernix granuloma
  • Amnion of the chorionic disc, placental membranes or umbilical cord
  • Result of deficient amniotic fluid over a prolonged period of time
Clinical features
  • Gross and histopathologic examination
Case reports
Gross description
  • Multiple firm, circumscribed, round to ovoid, raised, shiny, yellow nodules visible on the amniotic surface (Arch Pathol Lab Med 2007;131:1829)
  • 1 - 5 mm in diameter
Microscopic (histologic) description
  • Composed of varying proportions of squamous cells (occasionally keratinized), fat and hair embedded in degenerative amorphous acidophilic debris (Arch Pathol Lab Med 2007;131:1829)
Microscopic (histologic) images

Contributed by Caroline Simon, M.D.

Fetal squamous cells in amnion

Positive stains
  • Fetal skin cells within the amnion nodosum will stain positive for keratins
Electron microscopy description
  • Nodules are composed mostly of closely packed bundles of fibrillary material of high electron density and cellular elements of various kinds (Arch Pathol 1974;98:39)
  • Basement membrane of amnion epithelium is usually present under the nodules
Sample pathology report
  • Placenta, delivered:
    • Third trimester placenta 330 grams (tenth to twenty fifth percentile)
    • Umbilical cord: unremarkable 3 vessel cord
    • Fetal membranes and maternal decidua: amnion nodosum
    • Placental disc: villous maturation appropriate for gestational age; intervillous thrombus
Differential diagnosis
  • Squamous metaplasia:
    • Grossly typically more plaque-like, patchy and hydrophobic
    • Microscopically keratinizing metaplasia of the amnion
  • Chorion nodosum (Pediatr Dev Pathol 2006;9:353):
    • Similar nodules
    • Develop on the chorion
    • Associated with early amnion rupture / amniotic bands
Board review style question #1

The lesion in the image above is found in the placenta. What is the diagnosis?

  1. Acute chorioamnionitis
  2. Amnion nodosum
  3. Chorion nodosum
  4. Squamous metaplasia
Board review style answer #1
B. Amnion nodosum

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Reference: Amnion nodosum
Board review style question #2
Amnion nodosum is most commonly associated with which congenital anomaly / malformation?

  1. Renal agenesis
  2. Tracheoesophageal fistula
  3. Trisomy 18
  4. Ventricular septal defect
Board review style answer #2
A. Renal agenesis

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Reference: Amnion nodosum
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