VESICULAR MOLE
Gestational trophoblastic neoplasm (GTN) represents a spectrum of premalignant and malignant diseases that occur after abnormal fertilization. GTN includes complete hydatidiform mole (CHM), partial hydatidiform mole (PHM), invasive mole, choriocarcinoma, and placental-site trophoblastic tumor (PSTT). The following discussion is limited to CHM and PHM, which together account for 80% of all cases of GTN.
Sonography is the imaging investigation of choice for hydatidiform mole. Ultrasonography should include transabdominal and transvaginal real-time gray-scale imaging by using high-resolution equipment. Early literature described a snowstorm appearance consisting of several echogenic foci, but this finding is no longer seen with new high-resolution ultrasound equipment. With modern equipment, the typical sonographic appearance of CHM in the second and third trimesters is an enlarged uterine endometrial cavity containing innumerable anechoic cysts sized 1-30 mm. On pathologic examination, these cysts represent grossly swollen (hydropic) chorionic villi that have a bunch-of-grapes appearance.
In the first trimester, the sonographic appearance of CHM is relatively nonspecific. The classic finding of multiple, tiny, anechoic cystic spaces is rarely seen. The most common sonographic appearance of CHM in the first trimester is a homogeneously hyperechoic endometrial mass. An anembryonic gestation (empty gestational sac) may be the only sonographic finding; if it is, its distinction from blighted ovum is difficult or impossible.
Sonograms of PHM may show cystic changes similar to those of CHM but in a more focal distribution. The major distinguishing feature of PHM is embryonic tissue. In practice, PHM can be difficult to distinguish from CHM on sonograms, and this distinction is usually made pathologically. This limitation is insignificant because the management approaches are similar for CHM and for PHM.
Theca lutein ovarian cysts are present in 50% of hydatidiform moles. They result from ovarian hyperstimulation secondary to high circulating levels of beta-hCG. On sonograms, theca lutein cysts appear as large, septate cystic ovarian lesions. They may be unilateral or bilateral, and they may be extremely large. If the lesions are large, transabdominal scanning is needed to completely visualize them. The presence of bilateral and/or large theca luteins is well correlated with serum beta-hCG levels >100,000 mIU/mL. Theca lutein cysts usually resolve within 8-12 weeks after hydatidiform moles are evacuated. Cysts that persist after beta-hCG levels return to normal should prompt further workup to exclude a neoplastic process. In rare cases, theca lutein cysts rupture, hemorrhage, or cause ovarian torsion.
Doppler ultrasonography has no clearly defined role in the evaluation of hydatidiform mole. However, it is useful in diagnosing invasive forms of GTN, in which cystic vascular spaces with high-velocity, low-impedance flow are almost always demonstrated. Doppler ultrasonography also plays a role in monitoring the response of the disease after chemotherapy. Regression of cystic vascular masses is observed after successful treatment.