Over-diagnosis of hydatidiform mole in early tubal ectopic pregnancy

Aims: 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 tr eatment to a Supraregional Trophoblastic Tumour Screening and Treatment Cen tre between 1986 and 1996. Methods and results: Of 4261 women referred during the study period, 25 (0. 6%) had a suspected tubal ectopic hydatidiform mole and paraffin-embedded t issue was available in 20 (80%) of these, Each case was reviewed by two pat hologists and DNA flow cytometric analysis was undertaken when the histolog ical diagnosis was initially deemed equivocal or suggestive of hydatidiform mole. On review, 17 cases (85%) showed no evidence of hydatidiform mole (c ircumferential trophoblastic proliferation, hydrops, scalloped villi, and s tromal karyorrhexis), Of these, 11 cases (65%) showed features of early pla centation and six (35%) showed hydropic abortion. DNA flow cytometry was pe rformed in 14 (82%) of these cases and revealed a diploid population in eac h 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 o f these cases and confirmed the presence of diploidy in each. Conclusions: Our results show that tubal ectopic hydatidiform mole is a rar e entity and demonstrate that it is over-diagnosed. Polar trophoblastic pro liferation and hydropic villi are features of early placentation and of hyd ropic abortion. Sheets of extravillous trophoblast may be particularly prom inent in tubal ectopic gestation, In the absence of circumferential trophob lastic proliferation combined with hydropic change a diagnosis of gestation al trophoblastic disease should be avoided.