Overdiagnosis of complete and partial hydatidiform mole in tubal ectopic pregnancies

Partial or complete hydatidiform mole (HM) affects approximately 1 in 500 to 1,000 pregnancies. Previous small series suggest that histopathologic diagnosis of HM may be difficult in tubal ectopic pregnancies. The histopathology database of a regional Trophoblastic Disease Unit was searched to identify cases with a referral diagnosis of tubal HM, and the histopathologic findings were reviewed. During the study period (1986-2004 inclusive), there were 132 cases. After central review by specialist histopathologists, the final diagnosis was ectopic partial mole in two, ectopic complete mole in five, and ectopic hydatidiform mole (not otherwise specified) in one. The final diagnosis of definite hydatidiform mole was made in eight (6%) cases, significantly less than in referred uterine curettage specimens, in which approximately 90% have a confirmatory diagnosis of HM (Z = 12.9; p < 0.0001). No cases in this series developed persistent gestational trophoblastic disease, the human chorionic gonadotropin concentration spontaneously returning to normal. Ectopic pregnancies, where managed surgically, should be submitted for histopathologic examination; however, the pathologist should be aware that the degree of extravillus trophoblastic proliferation may appear more florid compared with evacuated uterine products of conception. Molar pregnancy should only be diagnosed when strict criteria regarding morphologic abnormalities previously described in uterine evacuation material are applied.