New insights in the pathophysiology of complete hydatidiform mole

The majority of complete hydatidiform moles (CHM) are detected on ultrasound examination by the end of the first trimester when they present as multiple sonolucent cysts. To better understand the pathophysiology of this unique placental pathology and improve its prenatal diagnosis and management we have reviewed the ultrasound features of CHM before the appearance of cystic changes.

We searched our database to identify all women diagnosed with a complete hydatidiform mole confirmed by histopathology who had an ultrasound examination before 9 weeks' gestation. We reviewed their ultrasound reports and all the corresponding images.

The study group included 39 women with a positive pregnancy test and vaginal bleeding, 36 of whom had at least two ultrasound examinations before 9 weeks' gestation. At the first scan (mean gestation age 7 + 1 weeks; SD 1.1), 29 out 39 (74.4%) of CHM presented as a heterogeneous hyperechogenic mass with or without gestational sac and the remaining ten (25.6%) cases as a regular 4-week gestational sac. Cystic molar changes became apparent from the end of the second month of gestation.

The development of a CHM follows a well-defined pattern starting with a macroscopically normal gestation sac at 4 weeks, which transforms into a polypoid mass between 5 and 7 weeks of gestation. The hydropic changes of the villous tissue is progressive and rarely visible in utero on ultrasound before 8 weeks of gestation. These findings should allow an earlier diagnosis and assist in the management counselling of women with CHM.