Invasive mole is a tumorous 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-metastasising neoplasms.
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.
Invasive moles arise from hydatidiform moles. There is an invasion of the myometrium by hydropic chorionic villi, accompanied by the proliferation of trophoblast. A tumour is locally destructive and may invade parametrial tissue and blood vessels.
As with other forms of the gestational trophoblastic disease, maternal serum βHCG values are markedly elevated.
Often it can be difficult to differentiate an invasive mole from other forms of gestational trophoblastic disease in imaging.
May be seen as an echogenic vascular mass invading the myometrium. Colour Doppler interrogation will show high velocity, low impedance flow.
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: isointense 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 a tumour into the myometrium, the invasive mole can appear as a more aggressive entity compared with a choriocarcinoma.
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