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Invasive mole is the less aggressive of the two forms of persistent gestational trophoblastic neoplasia and is seen in about 10% of patients after treatment of complete hydatidiform mole (and less frequently in patients with partial hydatidiform mole) (9). Patients present with bleeding and persistent elevations in the serum beta-hCG level. Imaging may show a central uterine process similar to that described for complete hydatidiform mole, occasionally with demonstrable myometrial invasion (Figure 9). This latter finding is inconsistently identified. However, because of the usual presence of characteristic clinical and chemical findings, documenting the presence of invasion is seldom needed. In fact, histologic confirmation of the diagnosis is usually not pursued. Besides, invasion is difficult to diagnose microscopically because the samples obtained by curettage seldom contain the intact myometrium required for this evaluation (2,11).
As with a complete hydatidiform mole, an invasive mole has hydropic villi, along with proliferation of the trophoblast. However, as the term invasive mole implies, there is macroscopic and microscopic invasion into the myometrium and blood vessels by the trophoblastic neoplasm itself (9,11). This appearance is similar to the normal vascular invasion that must occur as the early trophoblast establishes communication with the maternal circulation (17). Villous elements are occasionally seen in the maternal pulmonary circulation in normal third trimester pregnancies and in the peripartum period. Thus, although venous invasion, and occasionally spread to the lungs, may occur in the presence of an invasive mole, these metastases do not necessarily mean that the lesion is a true malignancy (2,9,11). From a practical standpoint, such a distinction is immaterial because both invasive mole and choriocarcinoma are treated with chemotherapy.
The most important use of US in the patient with suspected persistent gestational trophoblastic neoplasia is to exclude pregnancy as a cause for the elevated beta-hCG level. Occasionally, extension of the typically heterogeneous mass into the myometrium will be seen (18,19,20), as well as involvement of the parametrium.
Doppler US may be useful in the evaluation of GTD. These vascular tumors tend to show very high blood flow. More specifically, high diastolic flow, presumably the result of decreased vessel tone in the proliferating neoplasm, has been identified in patients with persistent gestational trophoblastic neoplasia (17,21,22). Although this decrease in uterine artery pulsatility may be of some use in diagnosing confusing cases that occasionally clinically mimic other conditions (eg, threatened abortion or uterine atony) (23,24), the persistently elevated beta-hCG level will usually indicate the diagnosis (25,26).
The use of MR imaging for evaluating these lesions has been described (27). In general, the lesions are heterogeneous, hypervascular masses that distort the normal zonal anatomy. Abnormal signal intensity may be seen in the myometrium or parametrium (Figure 10). The authors of one large series noted a return to a normal appearance after therapy and clinical resolution of the disease (27). The impact of MR imaging findings on management decisions was minimal (27). Therefore, rather than be a standard part of the evaluation, MR imaging is more likely to serve as a problem-solving tool in selected cases (25).
As previously mentioned, the treatment for either invasive mole or choriocarcinoma is generally chemotherapy. Exact histologic diagnosis, therefore, is not usually needed (28). A patient with persistent gestational trophoblastic neoplasia (typically, failure of the beta-hCG to return to undetectable levels after treatment of a complete hydatidiform mole) is presumed to have an invasive mole unless there is clinical or radiologic evidence for metastasis (6). Hysterectomy for invasive mole may be required if the patient is thought to be at risk for uterine perforation, but this is true in only a minority of cases.
Invasive Mole