Partial hydatidiform mole and placental mesenchymal dysplasia (PMD) can look remarkably similar on ultrasound
| Feature | Partial Hydatidiform Mole | Placental Mesenchymal Dysplasia (PMD) |
|---|---|---|
| Basic pathology | Abnormal trophoblastic proliferation with hydropic villi | Abnormal mesenchymal/stem-villus development with placental vascular abnormality |
| Genetics | Usually triploid, classically diandric triploidy | Usually biparental diploid fetus; placenta may show mosaic androgenetic/biparental pattern |
| Fetus | Often abnormal, growth restricted or may demise | Usually structurally normal, but Beckwith-Wiedemann syndrome (BWS) association |
| Placenta | Thickened, enlarged, multicystic/hydropic | Thick, enlarged, multicystic with hydropic-appearing villi |
| Cystic spaces | Usually relatively homogeneous hydropic/molar appearance | Cysts of variable size, often interspersed with recognizable placental tissue |
| Color Doppler | Vascularity not usually the dominant feature | Marked vascularity, dilated/tortuous vessels and sometimes thrombosis are characteristic |
| Cord/chorionic vessels | No characteristic vascular abnormality | Prominent, tortuous chorionic/stem-villus vessels |
| β-hCG | Usually clearly elevated | Usually normal or mildly elevated; can occasionally be elevated |
| Maternal AFP | May be normal or elevated depending on fetal/placental factors | Often disproportionately elevated |
| Maternal symptoms | Bleeding, hyperemesis, uterus large for dates may occur | Often asymptomatic |
| GTN risk | Yes | No gestational trophoblastic neoplasia risk |
| Pregnancy management | Generally evacuation | Pregnancy can usually be continued with close surveillance |
Ultrasound
Partial mole
Typical findings:
• Enlarged/thick placenta
• Multiple small cystic/hydropic areas
• Abnormal fetal anatomy is common
• Fetal growth restriction or demise may develop
• Fetal hydrops can occur
• Placental cystic change tends to represent hydropic villi
• Color Doppler does not typically show the striking tortuous vascular network characteristic of PMD.
The strongest clue is therefore an abnormal fetus + multicystic placenta.
PMD - placental mesenchymal dysplasia
The classic appearance is:
Large, thick placenta + multiple irregular cystic spaces + relatively normal fetus.
Look carefully with color Doppler for:
• Dilated chorionic vessels
• Tortuous stem vessels
• Increased intraplacental vascularity
• High-flow vascular channels
• Vascular thrombosis
• Cystic areas containing or adjacent to recognizable placental tissue
β-hCG is probably the most useful biochemical discriminator
Very high β-hCG
Think: Molar pregnancy
particularly if accompanied by:
• Hyperemesis
• Hyperthyroidism
• Enlarged uterus
• Theca-lutein cysts
• Classic molar placental morphology
Partial mole - Most are: 69,XXY / 69,XXX / 69,XYY
PMD - The fetus is generally: 46,XX or 46,XY biparental diploid.
PMD may be associated with Beckwith-Wiedemann syndrome, due to imprinting disorders at 11p15.5.
• Macrosomia
• Macroglossia
• Omphalocele
• Enlarged kidneys
• Adrenal abnormalities
• Hemihyperplasia
• Placentomegaly
Prognosis
Partial mole - The major issue persistent gestational trophoblastic disease.
The risk of persistent GTD/GTN is approximately 0.5–2%.
Fetal prognosis is generally poor because of:
• Triploidy
• Structural anomalies
• FGR
• Hydrops
• IUFD
Thus, once partial mole is confirmed, this is not a pregnancy that is managed expectantly as a normal ongoing pregnancy.
PMD
PMD has no intrinsic GTN risk, but fetal/perinatal complications can be substantial.
Reported complications include:
• FGR: approximately 33%
• IUFD: approximately 13%
• Preterm delivery: approximately 33%
Mechanisms is - abnormal placental vascularity → placental insufficiency → FGR/hypoxia/IUFD.