Over-diagnosis of hydatidiform mole in early tubal ectopic pregnancy

Tubal ectopic hydatidiform moles are rare lesions, and only 40 cases have been reported in the world literature. We investigated the apparently high incidence of tubal ectopic hydatidiform moles in women referred for treatment to a Supraregional Trophoblastic Tumour Screening and Treatment Centre between 1986 and 1996.

Of 4261 women referred during the study period, 25 (0.6%) had a suspected tubal ectopic hydatidiform mole and paraffin-embedded tissue was available in 20 (80%) of these. Each case was reviewed by two pathologists and DNA flow cytometric analysis was undertaken when the histological diagnosis was initially deemed equivocal or suggestive of hydatidiform mole. On review, 17 cases (85%) showed no evidence of hydatidiform mole (circumferential trophoblastic proliferation, hydrops, scalloped villi, and stromal karyorrhexis). Of these, 11 cases (65%) showed features of early placentation and six (35%) showed hydropic abortion. DNA flow cytometry was performed in 14 (82%) of these cases and revealed a diploid population in each case. Three cases of molar pregnancy (15%) were identified. Each of these cases had the histological features of an early complete hydatidiform mole. Sufficient tissue was available for DNA flow cytometric analysis in two of these cases and confirmed the presence of diploidy in each.

Our results show that tubal ectopic hydatidiform mole is a rare entity and demonstrate that it is over-diagnosed. Polar trophoblastic proliferation and hydropic villi are features of early placentation and of hydropic abortion. Sheets of extravillous trophoblast may be particularly prominent in tubal ectopic gestation. In the absence of circumferential trophoblastic proliferation combined with hydropic change a diagnosis of gestational trophoblastic disease should be avoided.