During the first trimester, the uterus may appear enlarged and filled with a hyperechoic mass with many cystic structures. The cysts measure 1 - 2 mm. and may not be seen sonographically. During the 2nd trimester, the cysts enlarge to approximately 2 cm. Thrombus and spontaneous abortion must be considered in the differential diagnosis. Diffuse involvement of the endometrial cavity, without the presence of an embryo, are findings consistent with a complete mole.
Malignant degeneration occurs more commonly with complete molar pregnancy.
An invasive mole is suspected when a well-circumscribed echogenic lesion is present within the uterine myometrium on ultrasound exam, following surgical removal of a molar pregnancy. This entity is distinguished from choriocarcinoma which occurs after a normal pregnancy, an ectopic pregnancy or spontaneous abortion. DNA studies reveal that the majority of hydatidiform moles to contain chromosomes of paternal origin. Imaging of Gestational Trophoblastic Disease.