chorionic anchoring villus

A chorionic anchoring villus is a specialized type of chorionic villus that physically connects the villous tree to the maternal uterine wall. It is the distal portion of a chorionic stem villus that is attached to the maternal decidua in early pregnancy and to the developing basal plate later in pregnancy through a column of cytotrophoblast cells.

A cytotrophoblast cell column is a column of proliferating cytotrophoblast cells extending from the tip of a chorionic anchoring villus to the maternal decidua. Cells at the base of this column break through the syncytiotrophoblast and invade the decidua and maternal spiral arteries, becoming the extravillous trophoblasts that remodel the uteroplacental vasculature.

Chorionic anchoring villi stabilize the position of the villous tree within the maternal intervillous bloodstream by providing fixed attachment points to the uterine wall. Without this anchoring, the floating villous tree would be dislodged by the flow of maternal blood through the intervillous space. The anchoring villi thus provide structural integrity to the entire placental attachment.

Anchoring villi are directly attached to the maternal uterine wall (decidua or basal plate) via the cytotrophoblast cell column, while chorionic floating villi are not attached to the maternal side and are freely immersed in maternal blood within the intervillous space. Floating villi are the primary site of gas and nutrient exchange, whereas anchoring villi are primarily structural.

Defective implantation and anchoring can result in placental abnormalities such as placenta accreta spectrum, where the cytotrophoblast cells invade too deeply into or through the myometrium (placenta accreta, increta, or percreta). Insufficient invasion by anchoring villus trophoblasts is associated with preeclampsia, where inadequate remodeling of spiral arteries leads to reduced uteroplacental blood flow and hypertensive disorders of pregnancy.