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Approximately 5% of cases of complete hydatidiform mole are followed by choriocarcinoma, although in the United States this number may be decreasing and may be less than 2% (29). Only about half the cases of choriocarcinoma arise from complete hydatidiform mole. An additional 25% of cases arise after normal pregnancies, and 25% follow spontaneous abortion or ectopic pregnancy (Figure 11) (9,10,29). Those cases that arise after complete hydatidiform mole are nearly all cured by chemotherapy (in contrast to the others, which have a less favorable prognosis). This difference may be due to the androgenetic character (exclusively paternal DNA) of the postmolar choriocarcinoma versus the biparental chromosomal makeup (identical to the fetus) of those cases that follow a normal gestation (29). Alternatively, the better prognosis may also result because patients with complete hydatidiform mole are identified to be "at risk" earlier than general postpartum patients, in whom the diagnosis would be relatively unsuspected (3,11).
At histologic evaluation, choriocarcinomas have extensive necrosis and hemorrhage. A biphasic population of cytotrophoblasts and syncytiotrophoblasts predominates (Figure 12); some intermediate trophoblasts may also be seen, but there are no villi. Early and extensive vascular invasion is common, which may result in metastatic disease even when the primary tumor is quite small. The gross morphologic characteristics reflect the aggressive, invasive nature of the lesion, with prominent hemorrhage and necrosis (Figure 13).
The presence of an elevated beta-hCG level in the absence of an intrauterine pregnancy gives reason to suspect GTD, including choriocarcinoma. As stated, half of all cases of choriocarcinoma occur in patients with prior complete hydatidiform mole who would be undergoing careful follow-up for the purpose of early detection of just such a lesion. Imaging thus has a limited role in the detection of the primary lesion but is useful in looking for metastasis. In addition, the extent of the intrauterine process itself is usually of limited importance, because the decision regarding surgical treatment is a clinical one (all patients are treated with chemotherapy) (6,30).
Regardless of the imaging modality used, choriocarcinoma often appears as a mass enlarging the uterus (Figure 12); sometimes it manifests as a discrete, central, infiltrative mass. Its heterogeneous appearance correlates with the necrosis and hemorrhage that characterize these lesions (Figure 12, Figure 13). Because extension of disease through the uterine wall and into the parametrium may alter decisions on medical and surgical management at some centers, CT may be useful for local disease assessment (31). Patients with large uterine tumors, especially those who do not desire future pregnancies, are occasionally treated with hysterectomy if there is substantial risk for uterine rupture.
Metastatic foci tend to show evidence for hemorrhage and may be quite large at the time of diagnosis (Figure 14, Figure 15). Although the search for metastatic disease varies with the experience of the practitioner and the clinical situation, chest radiography, chest CT, and head CT are frequent components of the work-up (25). Metastases to bone and lymph nodes are relatively uncommon (30).
As stated, although this is an aggressive malignancy, effective chemotherapy is available (28). Chemotherapeutic agents include methotrexate or actinomycin D, with or without additional agents such as cyclophosphamide (9,30). Clinical response is predicted on the basis of a complex staging system, which includes clinical factors (patient age, ABO blood grouping, prior chemotherapy, beta-hCG level) and radiologic findings (tumor size and the number and site of metastases) (30). Even in patients with metastatic disease, response rates exceed 85% and cure is common (2,3,11). Timely diagnosis contributes to the effectiveness of the treatment.
Choriocarcinoma