Trophoblast

Trophoblast is part of a normal pregnancy. Trophoblasts are derived from the conceptus, i.e. not maternal. Part of the trophoblast forms chorionic villi.

Tumours arising from the trophoblast are dealt with in gestational trophoblastic disease.

Trophoblast table

Based on Shih et al.:

	Cytotrophoblast	Syncytiotrophoblast	Villous intermediate trophoblast	Implanation site intermediate trophoblast	Chorionic-type intermediate trophoblast
Nuclear features	round, small	multinucleated	polyhedral	pleomorphic +/-multinucleation (occasional), +/-nucleoli	round / polyhedral
Cell borders	well-defined	poorly defined (?)	well-defined	moderately-defined	poorly defined (?)
Cytoplasm	minimal, clear to granular	abundant, vacuolated	abundant & eosinophilic to clear	abundant & eosinophilic	abundant & eosinophilic
Location	villi - deep to syncytiotrophoblast	villi - superficial to cytotrophoblast - nearest to maternal blood	villi	implanatation site	chorion
Function	stem cell, produces beta-hCG	produces hormones	???	anchor placenta	???
IHC	beta-hCG ???	beta-hCG	???	inhibin+, hPL+, beta-hCG-	???
Image	ST (jhu.edu)	CT (jhu.edu)		(WC)

hPL = human placental lactogen.

Notes:

• Keratin is positive in all trophoblastic tissue and negative in decidual tissue.

Chorionic villi

Chorionic villi 101

• Maternal blood is around villi.
• Fetal blood (nucleated (fetal) RBCs) in the villi.

Basic histology

• Outer layer of villus / closer to mother : syncytiotrophoblasts.
• Inner layer of villus / closer to fetus : cytotrophoblasts.
• Stroma of villi has macrophages AKA Hofbauer cells.

Chorionic villi 102

• Syncytiotrophoblasts (eosinophilic cytoplasm with vacuoles (contain hCG), multiple hyperchromatic nuclei).
  • Large + many irreg. or lobular hyperchromatic nuclei.
  • Eosinophilic vacuolated cytoplasm (contains hCG).
  • Closest to mom - covers cytotrophoblast.
• Cytotrophoblasts (polygonal shape, distinct borders, clear cytoplasm, in cords, single nucleus).
  • Polygonal shaped cells in cords/masses.
  • Distinct cell borders.
  • Covered by syncytiobrophoblast - closer to fetus than syncytiotrophoblasts.
  • Clear cytoplasm.
  • Single uniform nucleus.

Age of villi

Young villi

• Do not have blood vessels.
• No syncytial knots.

Old villi

• Blood vessels present and at the periphery of villus - contain nucleated (fetal) RBCs.
• Syncytial knots.

Villi and age - table

Gestational age	Nucleated RBCs	Cytotrophoblast / syncytiotrophoblast	Villi size	Vessels	Other
First trimester	present	both can be identified	large	few; location central
Second trimester	rare	cytotrophoblast difficult to identify; syncytial knots uncommon	intermediate	intermediate; location: central/periphery
Third trimester	absent	cytotrophoblast indistinct; syncytial knots common	small	abundant; location: periphery of villi	focal calcifications

Intermediate trophoblast

General

• Abbreviated: IT.

• Thought to be the cell of origin for:
  • Exaggerated placental site (EPS).
  • Placental site nodule (PSN).
  • Placental site trophoblastic tumour (PSTT).
  • Epithelioid trophoblastic tumour (ETT).

Subtypes

Three subtypes of IT are recognized:

1. Implanation site IT.
2. Villous IT.
3. Chorionic-type IT.

Microscopic

Features:

• Large cells.
• Eosinophilic cytoplasm.
  • May be multi-nucleated.

Images:

• IT - high mag. (jhu.edu).
• IT - high mag. (WC).
• IT - LMWK - high mag. (WC).

IHC

Features:

• hPL (human placental lactogen) +ve.
• beta-hCG -ve.
• Keratin +ve.
• EMA +ve in 2nd & 3rd trimester.
• CD146 +ve.

Notes:

• Cytotrophoblast and syncytiotrophoblast - keratin +ve.

See also

• Endometrium.
• Products of conception.
• Ectopic pregnancy.
• Choriocarcinoma.
• Arias-Stella reaction - benign atypical changes associated with chorionic tissue.

External links

• Uteroplacental Blood Flow: The Story of Decidualization, Menstruation and Trophoblast Invasion (yale.edu).