Clinical history: 29 year old female presented for routine fetal anatomy survey at 21 gestational weeks with high serum HCG.
What is the diagnosis?
Complete hydatidiform mole
The sections only contain chorionic villi. Fetal parts are not identified. There are markedly enlarged edematous villi showing central cisterns, and circumferential trophoblastic proliferation with marked cytologic atypia.
This is a complete hydatidiform mole (CHM). It shows typical characteristic features for a CHM, including markedly enlarged edematous villi, circumferential trophoblastic proliferation and marked cytologic atypia. In most cases, CHM is presented at earlier gestational weeks (<12 weeks), so called early CHM. The histological features of early CHM are subtle, including labyrinthine network of villous stromal canaliculi, hypercellular villous stroma with kayorrehexis, and some degree of trophoblastic atypia.
The differential diagnosis of CHM includes partial hydatidiform mole (PHM) and abnormal villous morphology due to other chromosomal abnormalities, such as trisomy or monosomy. In PHM, the fetal parts are present and the villi are often comprised of two distinct populations of either small fibrotic or large hydropic ones. The latter displays irregular scalloped villous contour and some degree of circumferential trophoblatic proliferation. In CHM, there is loss of p57 expression in the cytotrophoblast or stromal cells; however, staining for intermediate trophoblast is typical. The villi in trisomy and monosomy may show some irregular trophoblastic projections and stromal trophoblastic inclusions. Trophoblastic atypia are usually mild or absent.
Serum HCG is produced by syncytial trophoblasts and it is detectable one week post conception. Serum HCG peaks at around 12-14 gestational weeks and gradually decreases after that in the 2nd and 3rd trimesters. Abnormally high level of serum HCG is one of the clues for suspecting a molar pregnancy. Serum HCG level rapidly decreases after removal of placental tissue, and is therefore an extremely useful marker in following up patients with molar pregnancies. In consideration of the potential risk of developing an invasive mole and choriocarcinoma, the current clinical management of complete hydatidiform mole includes dilatation and curettage, weekly serum HCG titer measurement (until obtaining 3 consecutive negative results), and contraception for at least 6 months thereafter.