Placental Pathology

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Placental Anatomy & Development - Basic Blueprint

  • Dual Origin:
    • Fetal: Chorion frondosum (forms villi)
    • Maternal: Decidua basalis (basal plate)
  • Villous Development:
    • Primary (cytotrophoblast core)
    • Secondary (mesenchymal core)
    • Tertiary (vascularized); stem, intermediate & terminal villi.
  • Key Cells:
    • Syncytiotrophoblast (outer, multinucleated, hormones)
    • Cytotrophoblast (Langhans'; inner, proliferative)
    • Hofbauer cells (stromal macrophages)
  • Maternal Interface: Intervillous space (maternal blood); spiral artery remodeling crucial. Placental villous structure and circulation

⭐ Nitabuch's layer: Fibrinoid zone at utero-placental junction, limits placental invasion.

Placental Infections - Pathogen Parade

  • Routes: Ascending (commonest), hematogenous.
  • Chorioamnionitis: Maternal (chorion/amnion neutrophils) & Fetal (funisitis - umbilical cord vasculitis) response.
  • Villitis: Villi inflammation. Specific (CMV, Toxo) vs. VUE (Villitis of Unknown Etiology). Placental Pathology: Inflammation and Malperfusion
  • 📌 TORCH Infections:
    • Toxoplasma: Necrotizing villitis.
    • Others: Syphilis (large placenta, funisitis), Listeria (microabscesses), Varicella (necrotizing villitis, inclusions), Parvo B19 (hydrops, erythroblast inclusions).
    • Rubella: Mild villitis.
    • CMV: Plasma cell deciduitis, owl's eye inclusions.
    • HSV: Necrotizing villitis, inclusions.

⭐ Plasma cell deciduitis is highly suggestive of chronic endometritis and can be seen with certain infections like CMV.

Vascular & Implantation Disorders - Flow Failures

  • Placenta Previa: Painless APH. Types: complete, partial, marginal, low-lying. Risk: prior C-section. Placenta Previa, Accreta, Increta, Percreta Diagram
  • Placental Abruption: Painful APH, premature separation. Concealed/revealed. Risk: HTN. Couvelaire uterus.
  • Placenta Accreta Spectrum: Abnormal invasion.
    TypeDefinition
    AccretaVilli attach to myometrium (no decidua)
    IncretaVilli invade myometrium
    PercretaVilli penetrate serosa/adjacent organs

    ⭐ Prior Cesarean section is the single most important risk factor for placenta accreta spectrum disorders.

  • Maternal Floor Infarct: Basal plate fibrin deposition, ↓ perfusion. IUGR, stillbirth.
  • Fetal Thrombotic Vasculopathy: Fetal vessel thrombosis. Stillbirth, neuro injury.

Gestational Trophoblastic Disease - Molar Mayhem

  • Hydatidiform Mole: Abnormal trophoblast proliferation.
    • Complete (CM): 46,XX/XY (paternal). Diffuse villous edema ('grapes'), diffuse trophoblast hyperplasia. Markedly ↑hCG. p57KIP2 negative. Risk of choriocarcinoma ~15-20%. Partial, Complete, Invasive Moles, and Choriocarcinoma
    • Partial (PM): 69,XXY/XXX (triploid). Fetal parts; focal villous edema & trophoblast hyperplasia. Moderately ↑hCG. p57KIP2 positive. Risk <5%.
  • Invasive Mole: Mole invades myometrium. Persistent ↑hCG post-evac.
  • Choriocarcinoma: Malignant cyto/syncytio; NO villi. Hematogenous (lungs). Very ↑hCG.
  • PSTT (Placental Site Trophoblastic Tumor): Neoplastic intermediate trophoblasts. hPL positive; low hCG.

⭐ p57KIP2: Negative in CM (no maternal genome), Positive in PM (maternal genome present).

Other Placental Pathologies - Oddball Outcomes

  • Abnormal Shape/Size:
    • Bilobed: Two lobes.
    • Succenturiate: Accessory lobe; risk of retained products, PPH.
    • Circumvallate: Rolled edges, fibrin; ↑abruption, preterm labor.
    • Placenta Membranacea: Diffuse, thin placenta; accreta risk.
  • Cord Abnormalities:
    • Velamentous/Marginal Insertion: Unprotected vessels; risk of rupture, vasa previa.
    • True Knots: Can impede fetal circulation, fetal demise.
    • Vasa Previa: Fetal vessels overlie internal os; high fetal mortality if ruptured. Velamentous Cord Insertion and Vasa Previa

    ⭐ A single umbilical artery is associated with an increased risk of congenital anomalies, particularly cardiac and renal.

  • Meconium Staining:
    • Greenish discoloration of membranes/cord. Histo: meconium-laden macrophages in amnion/chorion.
  • Twin Placenta:
    • Determine chorionicity (mono/di) & amnionicity.
    • TTTS (Twin-Twin Transfusion Syndrome): Monochorionic; donor anemic, oligohydramnios; recipient polycythemic, polyhydramnios.

High‑Yield Points - ⚡ Biggest Takeaways

  • Placenta accreta spectrum: Abnormal adherence (accreta, increta, percreta); prior C-section is a major risk.
  • Abruptio placentae: Premature separation; painful bleeding, fetal distress, risk of DIC.
  • Placenta previa: Low implantation; painless 3rd-trimester bleeding.
  • Chorioamnionitis: Ascending infection; neutrophils in membranes, fetal tachycardia.
  • Complete mole: 46,XX (paternal), no fetus, diffuse villous edema, markedly ↑ hCG, ↑ choriocarcinoma risk.
  • Partial mole: Triploid (69,XXX/XXY), fetus present, focal edema, moderately ↑ hCG.

Practice Questions: Placental Pathology

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