Intermediate trophoblast

Intermediate trophoblast is a distinct subtype of trophoblastic tissue that arises from the cytotrophoblast.^[1]

Micrograph showing intermediate trophoblasts. H&E stain.

Implantation site intermediate trophoblast. Low molecular weight cytokeratin stain.

It is sub-categorized by location:^[1]

• Villous intermediate trophoblast:
  • at anchoring villi of trophoblastic column
• Implantation site intermediate trophoblast:
  • at implantation site (or basal plate), differentiated from villous intermediate trophoblast
• Chorionic-type intermediate trophoblast
  • at chorionic laeve of fetal membrane, differentiated from villous intermediate trophoblast

Function

The function of the implantation site intermediate trophoblast is to anchor the placenta to the maternal tissue.

Histomorphology

• Villous intermediate trophoblast^[1]
  • polyhedral and uniform nuclei
  • prominent cell border; abundant eosinophilic to clear cytoplasm
  • cohesive growth
• Implantation site intermediate trophoblast^[1]
  • pleomorphic irregular nuclei, large and hyperchromatic, may show multinucleation
  • abundant eosinophilic to amphophilic cytoplasm
  • infiltrative growth (splitting muscle, replacing vascular wall ...etc)
• Chorionic-type intermediate trophoblast^[1]
  • round to polyhedral nuclei, may multinucleation
  • abundant eosinophilic to clear cytoplasm
  • cohesive growth

Pathology

Intermediate trophoblasts are thought to be the cell of origin for:^[1]

• Exaggerated placental site (EPS): implantation site IT
• Placental site nodule (PSN): chorionic-type IT
• Placental site trophoblastic tumour (PSTT): implantation site IT
• Epithelioid trophoblastic tumour (ETT): chorionic-type IT