A hydatidiform mole is an abnormal pregnancy where the uterine cavity fills with numerous vesicular masses lacking complete fetal structures. These vesicles connect in clusters resembling grapes, hence the medical term "hydatidiform mole."
Although benign, 10%–25% of cases may undergo malignant transformation into invasive mole, causing local invasion or distant metastasis.Therefore, pregnant women should understand hydatidiform mole-related knowledge and take preventive measures.
I. Causes of Hydatidiform Mole
Experts note that the true cause of hydatidiform mole remains unknown. Past theories—including early embryonic death, nutritional factors, viral infections, and secondary polar body replication—have not been conclusively proven. Recent chromosomal studies suggest its occurrence is linked to abnormal fertilization of the egg or sperm.
The chromosomal karyotype of complete hydatidiform moles is predominantly 46XX, with a minority being 46XY. In these cases, the nuclear chromosomes of the egg lose activity. During fertilization, a haploid 23X sperm enters the egg nucleus, replicating to form 46XX, or two haploid sperm enter the egg nucleus, resulting in a karyotype of 46XX or 46XY.Partial hydatidiform moles predominantly exhibit trisomy karyotypes, most commonly 69XXY or 69XXX. This typically results from fertilization of a normal egg by two spermatozoa, or from fertilization of a normal egg by a spermatozoon with a meiotic error. These two types of moles represent distinct pathological entities; partial hydatidiform moles do not transform into complete hydatidiform moles.
II. Pathology of Hydatidiform Mole
1. Gross Examination: Placental villi form vesicles of varying sizes with thin, translucent walls containing viscous fluid. The spaces between vesicles are filled with blood and clots. The entire mass can enlarge the uterus to the size of a 24-26 week pregnancy.
2. Histological Features: Trophoblastic cells show varying degrees of hyperplasia. The intervillous stroma exhibits edema. Intramedullary vessels are absent or consist only of extremely sparse, non-functional vessels. Due to the persistent biological activity of trophoblastic cells, but lacking fetal circulation, the interstitial edema cannot be resolved. Consequently, fluid accumulates, causing the villi to swell and form vesicles.
III. Risk Factors for Hydatidiform Mole
1. Pregnancies occurring near the time of missed menstruation are prone to hydatidiform mole and choriocarcinoma.
2. Complete hydatidiform mole is the primary risk factor for choriocarcinoma.
3. Higher incidence rates are observed in Asian countries.
4. ABO blood types of the patient and her husband correlate with risk.