Question
Benign gestational trophoblastic diseases
Answer
Benign gestational trophoblastic diseases comprise a spectrum of proliferative disorders of pregnancy-associated trophoblastic tissue, the most important being the hydatidiform mole.
1. Complete hydatidiform mole:
- Karyotype: 46,XX (or occasionally 46,XY) — entirely paternal in origin, arising from fertilization of an “empty” ovum (lacking maternal chromosomes) by a haploid sperm that duplicates its own DNA, or by two sperm.
- No embryonic/fetal tissue is present.
- Gross: Bunch-of-grapes appearance — diffuse hydropic swelling of all chorionic villi.
- Microscopy: Diffuse trophoblastic (both cyto- and syncytiotrophoblast) hyperplasia with circumferential (marked) atypia, diffuse villous oedema with cistern formation, and absence of fetal vessels.
- hCG levels are markedly elevated.
- Higher risk (~2%) of progression to choriocarcinoma; ~15–20% risk of persistent/invasive mole.
2. Partial hydatidiform mole:
- Karyotype: Triploid (69,XXY or similar) — from fertilization of a normal ovum by two sperm (or one diploid sperm).
- Fetal/embryonic tissue (often with congenital anomalies) is usually present.
- Gross: Only some villi are hydropic; others are relatively normal.
- Microscopy: Focal (not diffuse) trophoblastic hyperplasia with mild atypia, scalloped villous contours, prominent stromal trophoblastic inclusions, and presence of fetal vessels (may contain nucleated fetal RBCs).
- Lower hCG elevation than complete mole.
- Low risk of choriocarcinoma; small risk of persistent mole.
3. Placental site nodule/exaggerated placental site (also benign): Localized, self-limited proliferations of intermediate trophoblast at the implantation site, usually incidental findings, distinguished from more aggressive placental site trophoblastic tumour by absence of significant mitotic activity/atypia.
Clinical significance: All forms present with vaginal bleeding, uterus larger than dates, and elevated β-hCG; ultrasound in complete mole classically shows a “snowstorm” pattern. Management is suction curettage with mandatory serial β-hCG follow-up to detect persistent/malignant trophoblastic disease.