When the vesicular tissue of a hydatidiform mole extends beyond the uterine cavity, invades deep into the myometrium, or metastasizes to other sites, it is referred to as a malignant hydatidiform mole. The chance of a hydatidiform mole transforming into a malignant hydatidiform mole or choriocarcinoma ranges from 5% to 20%. Most cases occur within six months after the evacuation of the hydatidiform mole, but malignant transformation can also occur before the mole is expelled. Although a malignant hydatidiform mole exhibits characteristics of malignancy, its treatment outcomes and prognosis are generally better than those of choriocarcinoma.

bubble_chart Pathological Changes

Grape-like structures are visible to the naked eye within the lesion, although in some cases they may not be apparent, yet microscopic examination reveals villous structures. Its invasive capability is stronger than that of a hydatidiform mole, often penetrating deep into the myometrium. Occasionally, it may perforate the uterine wall, causing perforation, or even infiltrate surrounding tissues, or metastasize to the lungs, vagina, and other sites. Microscopically, the lesion predominantly consists of proliferating trophoblastic cells, with visible villous structures, which distinguishes it from choriocarcinoma. There is often significant hemorrhage around the lesion.

bubble_chart Clinical Manifestations

1. Vaginal bleeding: After evacuation of a hydatidiform mole, there may be irregular vaginal bleeding of varying amounts. Upon examination, the uterus is slightly larger and softer than normal, and theca lutein cysts persist.

2. Manifestations of metastatic lesions: Hematogenous metastasis to the lungs may cause hemoptysis; metastasis to the vagina may present as purple-blue nodules on the vaginal mucosa, which can bleed when ulcerated. In rare cases of malignant hydatidiform mole, when chorionic villi erode and perforate the uterine muscle layer and serosal layer, it can lead to varying degrees of intra-abdominal bleeding, acute abdominal pain, and shock in cases of significant hemorrhage.

Diagnosis is based on medical history, clinical manifestations, and auxiliary examinations. The specific diagnostic criteria are as follows:

1. Urine pregnancy test: If the urine pregnancy test remains positive for more than 2 months after the evacuation of a hydatidiform mole, or turns positive again after being negative, with no residual vesicular mole confirmed by curettage, malignant transformation is possible.

2. Chest X-ray: Malignant hydatidiform mole often metastasizes to the lungs. Therefore, patients with cough or expectoration of blood must undergo pulmonary examination, which may reveal cotton-like shadows scattered throughout the lungs, especially in the lower lobe of the right lung. However, the absence of pulmonary lesions does not rule out invasive hydatidiform mole.

3. Diagnostic curettage: If only vaginal bleeding is present without other typical symptoms or signs, diagnostic curettage may be performed. If a small amount of decidua or necrotic tissue is obtained, invasive hydatidiform mole cannot be excluded.

bubble_chart Treatment Measures

Currently, the main treatment is chemotherapy, with the specific methods being the same as those for choriocarcinoma. For those who do not wish to have more children or are over 40 years old, a total hysterectomy may be performed.

bubble_chart Prognosis

After treatment, malignant hydatidiform mole generally has a good prognosis, but there is still a possibility of recurrence or progression to choriocarcinoma. Therefore, contraception should be advised for at least 2 years, and regular follow-up is necessary.

bubble_chart Metastasis and Spread

After the villi of a hydatidiform mole detach and enter the bloodstream, they can migrate to other parts of the body, damaging tissues and forming hematomas of varying sizes. This is another characteristic of malignant hydatidiform mole and serves as a useful criterion for distinguishing between benign and malignant forms. As previously mentioned, the trophoblastic cells of a normal pregnancy can also enter the maternal bloodstream and be found elsewhere in the body, but they do not cause any destructive lesions. Similarly, the villous epithelium of a benign hydatidiform mole may detach and travel through the bloodstream to other locations, much like any embolus from a destructive inflammatory process, but it does not cause local damage. Therefore, we consider cases where villi enter the bloodstream without causing destructive lesions at the site of migration as benign, while those causing damage are deemed malignant. It is worth noting that although the villi of a hydatidiform mole and the trophoblastic epithelium of a normal pregnancy can both enter the bloodstream, they differ in their biological and pathological characteristics. While neither causes local destruction, the former has a higher potential for malignant transformation. Additionally, malignant hydatidiform mole should be distinguished from true malignant tumors. Although both can metastasize and cause varying degrees of tissue damage at the metastatic sites, the metastases of a malignant mole may regress spontaneously, whereas malignant tumors rarely do.