Hydatidiform Mole

INTRODUCTION

Background: Gestational trophoblastic disease includes several disease processes that originate in the placenta. This includes complete and partial moles, placental site trophoblastic tumors, choriocarcinomas and invasive moles.

Almost all women with malignant gestational trophoblastic disease can be cured with preservation of reproductive function. The following discussion will be limited to hydatidiform moles, complete and partial.

Pathophysiology: A complete mole contains no fetal tissue. 90% are 46XX and 10% are 46XY. All chromosomes are of paternal origin. An enucleate egg is fertilized by a haploid sperm, which then duplicates its chromosomes, or the egg is fertilized by 2 sperm. In a complete mole the chorionic villi have grapelike (hydatidiform) swelling, and there is trophoblastic hyperplasia.

With a partial mole, fetal tissue is often present. The chromosomal complement is 69XXX or 69XXY. This results from fertilization of a haploid ovum and duplication of the paternal haploid chromosomes, or from dispermy. As in a complete mole, there is hyperplastic trophoblastic tissue and swelling of the chorionic villi.

Frequency:
　

• In the US: In western countries, 1:1000-1:1500 pregnancies are affected. It is an incidental finding in approximately 1 in 600 therapeutic abortions.

• Internationally: In Asian countries the rate is as much as 15 times higher than in the US. Japan has a reported rate of 2 per 1000 pregnancies. In the Far East, some sources estimate the rate as high as 1:120 pregnancies.

Mortality/Morbidity: Of patients with hydatidiform mole, 20% will develop a trophoblastic malignancy. After a complete mole, uterine invasion occurs in 15% of patients, and metastasis occurs in 4% of patients. No cases of choriocarcinoma have been reported after a partial mole, although 4% of patients with partial moles develop persistent nonmetastatic trophoblastic disease requiring chemotherapy.

Race: There is no racial/ethnic predilection for molar pregnancy. However, as discussed in the section on frequency, Asian countries show a rate 15 times higher than the US. Asian women living in the US do not appear to have a different rate of molar pregnancies than other ethnic groups.

Sex: Hydatidiform mole is a disease of pregnancy, and therefore a disease of women.

CLINICAL

History:

• Complete mole

• Vaginal bleeding - The most common symptom of a complete mole is vaginal bleeding. Molar tissue separates from the decidua, causing bleeding. The uterus may become distended by large amounts of blood, and dark fluid may leak into the vagina. This symptom occurs in 97% of cases.

• Hyperemesis - Patients may also complain of severe nausea and vomiting. This is due to extremely elevated hCG.

• Hyperthyroidism - Approximately 7% of patients may present with tachycardia, tremor, and warm skin.

• Partial mole

• Patients with partial mole do not have the same clinical features as complete mole. These patients usually present with signs and symptoms consistent with an incomplete or missed abortion.

• Vaginal bleeding

• Absence of fetal heart tones

Physical:

• Complete mole

• Size greater than dates - Uterine enlargement greater than expected for dates is a classic sign of a complete mole. This is due both to excessive trophoblastic growth and retained blood. However, a similar frequency of cases present as size appropriate for or smaller than expected for dates.

• Preeclampsia - Approximately 27% of patients with complete mole develop toxemia characterized by hypertension (BP>140/90), proteinuria (>300 mg/24h) and edema with hyperreflexia. Convulsions rarely occur.

• Theca lutein cysts - Ovarian cysts greater than 6 cm in size and accompanying ovarian enlargement. These cysts are usually not palpated on bimanual exam, but are identified by ultrasound. Patients may complain of pressure or pelvic pain, and because of the increased ovarian size, there is a risk of torsion. These cysts develop in response to high levels of Beta hCG, and regress spontaneously after the mole is evacuated.

• Partial mole

• Uterine enlargement and preeclampsia is reported in only 3% of patients.

• Theca lutein cysts, hyperemesis and hyperthyroidism are rare.

• Twinning with a complete mole and a fetus with a normal placenta has been reported. There have been case reports of healthy infants in these circumstances.

WORKUP

Lab Studies:
　

• Quantitative beta hCG - hCG levels greater than 100,000 mIU/mL indicates exuberant trophoblastic growth and should raise suspicion that a molar pregnancy should be ruled out. A molar pregnancy may have a normal hCG level.

• Complete blood count with platelets - Anemia is a common medical complication, as is the development of a coagulopathy.

• Test of clotting function to rule out the development of a coagulopathy, or to treat if one is discovered

• Liver function tests

• BUN and creatinine

• Thyroxin - Although women with molar pregnancies are usually clinically euthyroid, plasma thyroxin is usually elevated above normal pregnancy range. Also, hyperthyroidism may be the presenting complaint.

Imaging Studies:
　

• Ultrasound is the gold standard for identifying both complete and partial molar pregnancies. The classic image is of a snowstorm pattern indicating hydropic chorionic villi.

• Chest x-ray - Once a molar pregnancy is diagnosed a baseline chest film should be taken. The lungs are a primary site of metastasis for malignant trophoblastic tumors.

Histologic Findings: