Placenta
General
Normal histology

Author: Mandolin Ziadie, M.D. (see Authors page)

Revised: 11 October 2017, last major update June 2011

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

PubMed Search: Placenta histology [title]

Cite this page: Ziadie, M. Normal histology. PathologyOutlines.com website. http://pathologyoutlines.com/topic/placentanormalhistology.html. Accessed November 19th, 2017.
Basal plate (maternal surface)
  • Insertion site of the anchoring villi into maternal endometrium
  • Invasive intermediate trophoblasts are seen here
Chorionic plate (fetal surface)
  • Stem villi arising from umbilical vessels surrounded by connective tissue and fibrin
  • Covered by a layer of amnion and chorion
Placental villi
  • Capillaries, fetal macrophages (Hofbauer cells) and fibroblasts surrounded by trophoblast and syncytiotrophoblast layers
  • Site of gas exchange and waste elimination
  • Primary stem villi give off secondary stem villi which divide into tertiary stem villi, which form the placental lobules and insert into the basal plate
  • They then give off branches to form the terminal villous units
Cells
Cytotrophoblast:
  • Present in early gestation; differentiates into villous or extravillous trophoblast (see below) and forms syncytiotrophoblasts by fusing on villous surface
  • They are inconspicuous in term placenta
  • Microscopic (histologic) description: small, round mononuclear cells with distinct cell border, minimal clear or eosinophilic cytoplasm and single vesicular nuclei
  • Positive stains (early placenta): AE1 / AE3 (keratin) and Ki67 (25 - 50%)
  • Negative stains (early placenta): EMA, hCG, HLA-G, HNK-1, hPL, inhibin alpha, MEL-CAM (CD146) and PLAP

Intermediate implantation site and extravillous (X cells) trophoblasts:
  • Infiltrate decidua and myometrium of placental site, invade and replace spiral arteries of the basal plate to establish maternal - fetal circulation and keep vessels patent
  • Form trophoblastic shell
  • Secrete PTH related protein
  • Microscopic (histologic) description: located in the basal plate, septa and chorion lavae; morphology varies by location
    • In the basal plate, they are enlarged polyhedral to spindle cells with abundant amphophilic and vacuolated cytoplasmic and large, hyperchromatic nuclei and may resemble adjacent decidua
    • In myometrium are more spindled and resemble adjacent smooth muscle cells; may fuse to become multinucleated cells (Am J Surg Pathol 1992;16:1226)
  • Microscopic (histologic) images:

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Intermediate trophoblast cells

  • Positive stains: cytokeratin (Mod Pathol 1990;3:282), hCG (in multinucleated cells), HLA-G, hPL, MEL-CAM and PLAP (weak)
  • Negative stains: EMA (usually), HNK-1 and Ki67

Intermediate villous trophoblast:
  • Form the inner layer of the villous trophoblastic mantle
  • Microscopic (histologic) description: larger than cytotrophoblasts, polygonal, abundant clear or eosinophilic cytoplasm, distinct cell borders and single nuclei
  • Positive stains: cytokeratin, EMA, HLA-G, hPL and MEL-CAM (in cells with eosinophilic cytoplasm; towards distal end only), PLAP (in clear cells), Ki67 (3 - 10%; > 90%)
  • Negative stains: EMA, hCG, hPL (may be weak), PLAP and HNK-1
  • Additional references: Am J Surg Pathol 2002;26:914

Syncytiotrophoblast:
  • Form the outer layer of the villous trophoblastic mantle
  • Synthesize and secrete hCG, hPL
  • Microscopic (histologic) description: multinucleated giant cells with abundant eosinophilic or basophilic cytoplasm, often with multiple intracytoplasmic vacuoles and dense pyknotic nuclei
  • Positive stains: hCG, hPL and inhibin alpha
  • Negative stains: HLA-G, Ki67, MEL-CAM and PLAP
  • Electron microscopy description: vacuoles are due to dilated endoplasmic reticulum and lacunae from plasma membrane infoldings

Hofbauer cells:
  • Fetal macrophages located in villous stroma
  • Microscopic (histologic) description: round to ovoid cells with eccentric nuclei and granular cytoplasm