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Placenta - Pathology

Hydatidiform mole (molar pregnancy) is a tumor of placental trophoblastic tissue. Incidence in the United States is 1 per 1,000 pregnancies, with an even higher inci-dence in Asia.


Hydatidiform mole (molar pregnancy) is a tumor of placental trophoblastic tissue. Incidence in the United States is 1 per 1,000 pregnancies, with an even higher inci-dence in Asia. Women ages <15 and >40 are at increased risk.

Complete mole results from fertilization of an ovum that lost all of its chro-mosomal material, so that all chromosomal material is derived from sperm.

         90% of the time, the molar karyotype is 46,XX

         10% of the time, the molar karyotype includes a Y chromosome

         The embryo does not develop

Partial mole results from fertilization of an ovum (that has not lost its chro-mosomal material) by 2 sperms, one 23,X and one 23,Y.

         Results in a triploid cell 69, XXY (23,X [maternal] + 23,X [one sperm] + 23,Y [the other sperm])

         The embryo may develop for a few weeks

Patients with hydatidiform mole typically present with the following:

         Excessive uterine enlargement (“size greater than dates”)

         Vaginal bleeding

         Passage of edematous, grape-like soft tissue

         Elevated beta-human chorionic gonadotropin (β-hCG)

Microscopically, molar tissue will show edematous chorionic villi, trophoblast pro-liferation, and fetal tissue (only in partial mole). Diagnosis is by U/S. Treatment is endometrial curettage and following of β-hCG levels.

Invasive mole is a mole that invades the myometrium of the uterine wall.

Choriocarcinoma is a malignant germ cell tumor derived from the trophoblast that forms a necrotic and hemorrhagic mass. Almost 50% arise from complete moles. The most common presentation is a rising or plateaued titer of hCG after a molar pregnancy, abortion, or ectopic pregnancy.

Microscopically, choriocarcinoma shows proliferation of cytotrophoblasts, interme-diate trophoblasts, and syncytiotrophoblasts. Hematogenous spread can occur, with seeding of tumor to lungs, brain, liver, etc. Treatment is chemotherapy.

Placental site trophoblastic tumor is a tumor of intermediate trophoblast which usually presents <2 years after pregnancy with bleeding and an enlarged uterus. Treatment is surgical; it does not respond well to chemotherapy.

In ectopic pregnancy, the fetus implants outside the normal location, most often in the fallopian tube, and less often in the ovaries or abdominal cavity. The fetus almost never survives. The mother is at risk for potentially fatal intra-abdominal hemorrhage. Risk factors include scarring of fallopian tubes from PID, endometrio-sis, and decreased tubal motility.

Enlarged placenta is common with maternal diabetes mellitus, Rh hemolytic dis-ease, and congenital syphilis.

Succenturiate lobes are accessory lobes of the placenta which may cause hemorrhage if torn away from the main part of the placenta during delivery.

Placental abruption is partial premature separation of the placenta away from the endometrium, with resulting hemorrhage and clot formation. Risk factors include hypertension, cigarette use, cocaine, and older maternal age.

Placenta previa describes when the placenta overlies the cervical os. Vaginal delivery can cause the placenta to tear, with potentially fatal maternal or fetal hemorrhage.

In placenta accreta, the placenta implants directly in the myometrium rather than in endometrium. Hysterectomy is required after delivery to remove the rest of the placenta.

Twin placentation

         Fraternal twins always have 2 amnions and 2 chorions; placental discs are usually separate, but can grow together to appear to be a single placental disc.

         Identical twins have a variable pattern in the number of membranes and discs due to variations in the specific point in embryonic development at which the twins separated. Twin-twin transfusion syndrome can occur if (a) there is only one placental disc and (b) one twin’s placental vessels connect to the other twin’s placental vessels.

         Conjoined twins are always identical twins with one amnion, one chorion, and one disc, though there are rare reports of diamniotic placentation.

Preeclampsia is a condition of new onset hypertension and either proteinuria or end-organ dysfunction after 20 weeks gestation in a previously normotensive woman. It is linked to abnormal uteroplacental blood flow.

         The term eclampsia is used when the patient has seizures not attributable to other causes.

         HELLP syndrome is a rare complication of preeclampsia characterized by hemolysis, elevated liver enzymes, and low platelets.

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