Placental Pathology

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.

⭐ 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).

• 📌 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.

• Placental Abruption: Painful APH, premature separation. Concealed/revealed. Risk: HTN. Couvelaire uterus.

• Placenta Accreta Spectrum: Abnormal invasion.

  Type	Definition
  Accreta	Villi attach to myometrium (no decidua)
  Increta	Villi invade myometrium
  Percreta	Villi 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 (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.

  ⭐ 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.