Trophoblast

Chorionic villi are part of a normal pregnancy. They are derived from the conceptus, i.e. NOT maternal.

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

Chorionic villi 101

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

Basic histology

• Outer layer of villus: syncytiotrophoblasts.
• Beneath syncytiotrophoblast (and closer to fetus) cytotrophoblasts.

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.

Implantation site

• Intermediate trophoblast.

IHC

Features:

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

Notes:

• Cytotrophoblast and syncytiotrophoblast - keratin +ve.

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.

See also

• Endometrium.
• Products of conception.
• Ectopic pregnancy.
• Choriocarcinoma.