Definition/General
Introduction:
Partial hydatidiform mole (PHM) is a gestational trophoblastic disease characterized by focal villous enlargement
It shows focal trophoblastic proliferation with coexistent fetal tissue
It represents a triploid conception with two paternal and one maternal haploid genome
It carries lower malignant potential than complete mole.
Origin:
Arises from dispermic fertilization of normal ovum resulting in triploidy
Most commonly 69,XXY (60% cases)
Less commonly 69,XXX (37% cases) or 69,XYY (3% cases)
Results in diandric triploidy (two paternal, one maternal genome)
Leads to abnormal placental development.
Classification:
Classified as gestational trophoblastic disease (GTD)
Part of spectrum with complete mole
Invasive mole
Choriocarcinoma
Has lower malignant potential than complete mole
Risk of GTN approximately 2-5%.
Epidemiology:
Less common than complete mole
Incidence approximately 1:1000-2000 pregnancies
More common in Western populations compared to complete mole
Peak incidence in reproductive age women
Associated with advanced paternal age in some cases.
Clinical Features
Presentation:
Missed abortion or incomplete abortion (most common)
Vaginal bleeding (usually less severe than complete mole)
Uterine size smaller than dates
May have fetal heart activity initially
Growth restriction if fetus survives
Fetal anomalies (syndactyly, growth restriction)
Preeclampsia (rare, <2%).
Symptoms:
Irregular vaginal bleeding
Abdominal cramping
Symptoms of missed abortion
Less severe hyperemesis than complete mole
Passage of vesicular tissue (occasionally)
Absence of fetal movement (if fetus present).
Risk Factors:
Advanced paternal age (some studies)
Previous history of molar pregnancy
Multiple ovulation (rare association)
Familial recurrent molar pregnancies
Consanguineous marriage (rare)
No strong maternal age association.
Screening:
Serum beta-hCG levels (moderately elevated or normal for gestational age)
Pelvic ultrasound showing focal cystic changes
Complete blood count
Karyotype analysis of products of conception
Pathological examination essential for diagnosis.
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Gross Description
Appearance:
Mixed tissue with both normal and abnormal placental tissue
Focal vesicular change affecting portion of placenta
Some villi appear normal while others are enlarged
Fetal parts may be identified
Ratio of normal to abnormal villi variable.
Characteristics:
Combination of normal-sized and enlarged villi
Vesicular change is focal rather than diffuse
May have identifiable fetal tissues
Amniotic membrane may be present
Overall specimen size usually normal or small.
Size Location:
Involves portion of placental tissue (focal involvement)
Normal villi interspersed with enlarged villi
Vesicle size typically smaller than complete mole
May have geographic distribution
Fetal tissue size varies.
Multifocality:
Shows patchy involvement of placental tissue
Normal and abnormal villi intermixed
Skip lesions may be present
Focal trophoblastic proliferation
Variable distribution throughout placenta.
Microscopic Description
Histological Features:
Focal villous enlargement with scalloped villous outlines
Trophoblastic inclusions within villous stroma
Focal trophoblastic proliferation (less marked than complete mole)
Fetal blood vessels may be present in some villi
Normal villi interspersed with abnormal ones.
Cellular Characteristics:
Trophoblastic cells show mild to moderate atypia
Less pronounced than complete mole
Fetal erythrocytes may be present in villous vessels
Syncytiotrophoblast shows pseudoinclusions
Cytotrophoblast proliferation focal.
Architectural Patterns:
Scalloped villous outlines characteristic feature
Some villi show central cavitation
Dual population of normal and abnormal villi
Trophoblastic inclusions pathognomonic
May show capillary proliferation in some villi.
Grading Criteria:
Degree of trophoblastic proliferation (usually mild to moderate)
Proportion of abnormal villi (variable, typically <50%)
Presence of trophoblastic inclusions
Degree of villous enlargement
Scalloping of villous outline.
Immunohistochemistry
Positive Markers:
p57 (positive in villous cytotrophoblast and stromal cells, diagnostic)
Beta-hCG (positive in syncytiotrophoblast)
hPL (human placental lactogen)
Inhibin-alpha (positive in cytotrophoblast)
Cytokeratin (broad spectrum).
Negative Markers:
CD68 (negative in trophoblast)
Smooth muscle actin (negative in trophoblast)
S-100 (negative)
Melanoma markers (negative)
p53 (usually negative or weak).
Diagnostic Utility:
p57 immunostaining is diagnostic (positive in partial mole, negative in complete mole)
Essential for differential diagnosis
Confirms trophoblastic origin
Helps distinguish from hydropic abortion
Most reliable diagnostic marker.
Molecular Subtypes:
Partial mole shows triploid pattern
Most common 69,XXY (diandric triploidy)
Less common 69,XXX or 69,XYY
Two paternal, one maternal genome contribution
Results in abnormal genomic imprinting.
Molecular/Genetic
Genetic Mutations:
Triploid genome (69 chromosomes)
Most common: 69,XXY from dispermic fertilization
Diandric triploidy (two paternal genomes)
Results in abnormal genomic imprinting
Imbalance in parental genome contribution.
Molecular Markers:
Flow cytometry shows triploid DNA content
Microsatellite analysis confirms triploidy
p57 protein expression present (maternal gene active)
Karyotype analysis shows 69 chromosomes
DNA fingerprinting confirms parental contributions.
Prognostic Significance:
Lower risk of GTN (2-5%) compared to complete mole
Risk factors for GTN progression include: degree of trophoblastic proliferation
Persistently elevated hCG levels
Clinical presentation
Overall better prognosis than complete mole.
Therapeutic Targets:
Serial hCG monitoring (shorter duration than complete mole)
Less intensive surveillance required
Chemotherapy rarely needed
Contraception during surveillance period
Earlier return to normal hCG levels expected.
Differential Diagnosis
Similar Entities:
Complete hydatidiform mole (p57 negative, no fetal parts, diploid)
Hydropic abortion (p57 positive, normal trophoblast, diploid)
Twin pregnancy with mole
Triploidy without molar features
Spontaneous abortion with hydropic change.
Distinguishing Features:
Partial mole: p57 positive
Partial mole: Focal villous change
Partial mole: Fetal parts present
Complete mole: p57 negative
Complete mole: Diffuse villous change
Complete mole: No fetal parts
Hydropic abortion: Normal trophoblast
Hydropic abortion: No trophoblastic inclusions.
Diagnostic Challenges:
Distinguishing from hydropic abortion (trophoblastic inclusions key feature)
Early partial mole recognition
p57 immunostaining essential
Molecular studies for confirmation
Assessment of trophoblastic proliferation degree.
Rare Variants:
Partial mole with minimal changes
Partial mole with coexistent normal twin
Atypical partial mole with prominent trophoblastic proliferation
Invasive partial mole (rare)
Choriocarcinoma following partial mole (very rare).
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
Products of conception, measuring [size], with [presence/absence] of fetal parts
Diagnosis
Partial Hydatidiform Mole (Gestational Trophoblastic Disease)
Classification
Classification: Partial mole with [degree] trophoblastic proliferation
Histological Features
Shows focal villous enlargement with scalloped outlines and trophoblastic inclusions
Immunohistochemistry
p57: Positive (diagnostic of partial mole), hCG: Positive in syncytiotrophoblast
Genetic Analysis
Molecular analysis: [triploid pattern/pending] consistent with partial mole
Risk Assessment
Low risk for GTN progression (2-5% risk) based on partial mole diagnosis
Recommendations
Serial serum hCG monitoring recommended. Shorter surveillance period than complete mole. Clinical correlation advised.
Final Diagnosis
Partial Hydatidiform Mole with low risk of progression to GTN