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Placenta

Gestational trophoblastic disease

Incomplete / partial mole


Reviewer: Mandolin Ziadie, M.D. (see Reviewers page)
Revised: 10 December 2011, last major update December 2011
Copyright: (c) 2003-2011, PathologyOutlines.com, Inc.

Definition
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● 20% of all moles
● 9% of spontaneous abortions
● Triploid or tetraploid, some are trisomy 16
● A variable percentage (up to 86% in some studies) of triploid abortuses may have histologic features of partial moles (Hum Pathol 1996;27:1018), but many cases are actually due to extra maternal genome (digynic zygotes)
● Note: not all triploid conceptuses show molar transformation, although most die at age 8 weeks
● Diandric; contains extra set of paternal chromosomes due to fertilization by two sperm or by a single diploid sperm
● Diagnosed in second trimester or later
● Patients have small-for-date uteri without marked hCG elevation
● May be associated with toxemia of pregnancy; may present as missed or spontaneous abortion
● 4-12% develop persistent gestational trophoblastic disease; very low risk of choriocarcinoma; invasive mole rare; persistent intrauterine disease may develop

Treatment
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● Closely monitor hCG
● Chest Xray

Gross description
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● Smaller volume of tissue than complete mole (200 ml or less)
● Mixture of grossly vesicular and normal villi
● Fetus / embryo is usually present, although often abnormal (blighted ovum) or with syndactyly of digits 3 & 4 of both hands and feet

Gross images
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Partial hydatidiform mole

Micro description
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● Mixture of edematous villi similar to complete mole and relatively normal villi (Hum Pathol 2000;31:914, Hum Pathol 1981;12:1016)
● Less conspicuous central cistern formation (internal clefting)
● Mild focal trophoblast hyperplasia without atypia
● Villous scalloping (invaginations of trophoblast tissue into villous stroma, appears circular in cross section and resembles “coast of Norway” or inclusions)
● Smaller villi usually have stromal fibrosis
● Villi have vessels with nucleated RBCs if fetal development present

Micro images
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Minimal trophoblastic proliferation; some have hydropic villi

Positive stains
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● p57KIP2, p53 (Mod Pathol 1996;9:392), hCG

Molecular description
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● 58% XXY, 40% XXX, 2% XYY
● Ploidy analysis useful for diagnosis (Arch Pathol Lab Med 1998;122:1000)

Differential diagnosis
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● Trisomic pregnancies
● Early / hydropic abortions (polar trophoblastic hyperplasia, no cisterns and no atypia)
● Blighted ovum (early demise of embryo, usually is smaller, villi only slightly enlarged, only focal cisterns, no grossly enlarged villi and no trophoblastic atypia)
● Choriocarcinoma or placental site trophoblastic tumor (no villi)

End of Placenta > Gestational trophoblastic disease > Incomplete / partial mole


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