Complete hydatidiform mole

Last revised by Ammar Ashraf on 18 Jun 2023

A complete hydatidiform mole (CHM) is a type of molar pregnancy and falls at the benign end of the spectrum of gestational trophoblastic disease

A complete hydatidiform mole is the commonest type of gestational trophoblastic disease.

Complete moles are characterized by the absence of a fetus or fetal parts (i.e. no embryonic tissues). There is a non-invasive, diffuse swelling of chorionic villi.

Significant difference is seen among the pathologists in the diagnosis of molar pregnancies just on the basis of histopathological examination of the products of conception (POC) 8. The p57KIP2 gene is paternally imprinted and expressed from the maternal allele 8,9. Polymer-based immunohistochemistry (IHC) with p57, shows absent staining in the complete mole (CM) and positive staining in the hydropic abortus (HA) and partial mole (PM) 8,9. This IHC staining is a useful and inexpensive tool which can help in distinguishing complete mole from its mimics and can avoid DNA analysis 8,9.

Approximately 90% of complete hydatidiform moles have a 46XX diploid chromosomal pattern with ~10% having a 46XY composition. All the chromosomes are derived from the sperm, suggesting fertilisation of a single egg that has lost its chromosomes.

Serum beta HCG levels are markedly elevated, out of proportion to the pregnancy. 

  • enlarged uterus

  • may be seen as an intrauterine mass with cystic spaces without any associated fetal parts

  • may be difficult to diagnose in the first trimester 6

    • may appear similar to a normal pregnancy or as an empty gestational sac

    • <50% are diagnosed in the first trimester

  • bilateral theca lutein cysts may also be seen on ultrasound

  • color Doppler interrogation may show high velocity with a low impedance flow

CT evaluation is not usually performed due to its low resolution for the uterine assessment. CT may show an enlarged uterus with areas of low attenuation, or hypoattenuating foci surrounded by highly enhanced areas in the myometrium.

MRI may demonstrate a heterogeneous mass with cystic spaces distending the uterine cavity. Fetal parts are notably absent. Uterine zonal anatomy is often distorted although a hypointense irregular myometrial boundary may be seen 3.

  • T1: there may be areas of high signal corresponding to foci of hemorrhage

  • T2: there is heterogeneous high signal from the cystic spaces

  • T1 C+ (Gd): often demonstrates intense enhancement due to hypervascularity

MRI may also demonstrate bilateral theca lutein cysts.

Suction and curettage are used for evacuation and are usually the routine treatment. Serial beta hCG levels are performed until it is no longer detectable on the assay, as it is the main indicator of residual disease.

A complete mole is itself benign but is considered a premalignant lesion. Degeneration into more invasive and malignant types of gestational trophoblastic disease can occur in ~10-20% of cases.

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