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Invasive mole

An invasive mole is a tumourous growth associated with gestation and falls under the spectrum of gestational trophoblastic disease. Due to their aggressive growth characteristics, invasive moles are considered locally invasive non-metastasizing neoplasms.

Epidemiology

An invasive mole develops in approximately 10-20% of patients after molar evacuation and infrequently after other gestations. It is defined as a mole that penetrates and may even perforate the uterine wall.

Pathology

There is invasion of the myometrium by hydropic chorionic villi, accompanied by proliferation of trophoblast. The tumour is locally destructive and may invade parametrial tisue and blood vessels.

Markers

As with other form of gestational trophoblastic disease, maternal serum beta HCG values are markedly elevated.

Radiographic features

Often it can be difficult to differentiate an invasive mole from other forms of gestational trophoblastic disease in imaging. 

Pelvic ultrasound

May be seen as an echogenic vascular mass invading the myometrium. Colour Doppler interrogation will show high velocity, low impedence flow.

Pelvic MRI

On MRI, it often appears as a poorly defined mass that deeply invades the myometrium. Complete or partial disruption of the junctional zone may also be seen.

Typical signal characteristics include:

  • T1: iso-intense to the myometrium with scattered foci of high signal intensity (from  the presence of haemorrhage)
  • T2: mixed signal intensity

Molar-like structures appear as tiny cystic lesions within the well-enhanced zone of trophoblastic proliferation in a mass of the invasive mole.

With the penetration of the tumour into the myometrium, the invasive mole can appear as a more aggressive entity compared with a choriocarcinoma.

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