Topics

Topic

design image
Placenta

The placenta is a temporary but vital organ of pregnancy that develops in the uterine wall. It provides the interface between mother and fetus, facilitating exchange of oxygen, nutrients, and waste products. It also produces essential hormones required to maintain pregnancy.

Anatomically, the placenta is discoid in shape, with a maternal surface (attached to uterine wall) and a fetal surface (covered by chorionic plate and connected to umbilical cord). The placental villi project into the intervillous space, enabling maternal-fetal exchange.

Synonyms

  • Afterbirth (clinical term, postpartum)

  • Placental disc

  • Chorionic placenta

Structure

  • Maternal surface: Rough, lobulated, attached to endometrium (decidua basalis)

  • Fetal surface: Smooth, shiny, covered by amnion, with insertion of umbilical cord

  • Functional units: Chorionic villi bathed in maternal blood within the intervillous space

  • Membranes: Amnion and chorion contribute to placental covering and sac formation

Relations

  • Maternal side: Endometrium (decidua basalis) of uterus

  • Fetal side: Amniotic cavity, fetus, and umbilical cord

  • Vascular relations: Maternal spiral arteries supply blood to intervillous space; fetal umbilical vessels drain into the cord

Function

  • Facilitates maternal-fetal exchange of oxygen, nutrients, and waste products

  • Produces hormones (hCG, progesterone, estrogens, human placental lactogen)

  • Acts as an immunological barrier protecting fetus from rejection

  • Provides mechanical protection and anchorage of fetus to uterine wall

Clinical Significance

  • Placenta previa: Low-lying placenta covering cervix

  • Placental abruption: Premature separation from uterine wall

  • Placenta accreta spectrum: Abnormal adherence or invasion into myometrium

  • Placental infarction/insufficiency: Associated with fetal growth restriction

  • Tumors (chorangioma): Rare vascular lesions of placenta

  • Imaging: MRI is used when ultrasound is inconclusive, especially in placenta accreta spectrum

MRI Appearance

T2 HASTE (T2 GRE):

  • Placenta shows intermediate to slightly hyperintense signal compared to myometrium

  • Intervillous blood spaces and venous lakes appear as hyperintense foci

  • Areas of infarction or calcification appear hypointense

  • Abnormal invasion (placenta accreta/increta): heterogeneous signal with dark intraplacental bands

T1 GRE:

  • Placenta shows isointense to mildly hyperintense signal relative to myometrium

  • Hemorrhage (retroplacental or intraplacental) appears bright hyperintense

  • Normal intervillous spaces are not well delineated on T1

MRI image

Placenta MRI axial anatomy image-img-00000-00000

MRI image

Placenta MRI CORONAL MRI IMAGE