Partial hydatidiform mole is optimally diagnosed histopathologically when four microscopic features coexist: 1) two populations of villi, 2) enlarged villi (≥3–4 mm) with central captivation, 3) irregular villi with geographic, scalloped borders with trophoblast inclusions, and 4) trophoblast hyperplasia (usually focal and involving syncytiotrophoblast). Pathologic mimics of partial mole include Beckwith-Wiedemann syndrome, placental angiomatous malformation, twin gestation with complete mole and existing fetus, early complete hydatidiform mole, and hydropic spontaneous abortion. Because partial hydatidiform mole results from diandric triploidy, flow cytometry (or another method to assess ploidy) can be utilized by pathologists for supporting diagnostic classification of problematic specimens, or for educational or quality assurance purposes. Confirmation of the histopathologic diagnosis by ploidy or molecular studies is important for scientific reports of partial hydatidiform mole, especially when unusual or aggressive outcomes (such as choriocarcinoma) are reported.
Division of Women's and Perinatal Pathology, Department of Pathology, Brigham and Women's Hospital, Boston, Massachusetts.
Presented in part at the Annual Meeting of the International Society of Gynecological Pathologists held in conjunction with the United States Division of the International Academy of Pathology, Atlanta, Georgia, March 4, 2001.
Address correspondence and reprint requests to David R. Genest, M.D., Division of Women's and Perinatal Pathology, Department of Pathology, Brigham and Women's Hospital, 75 Francis Street, Boston, MA 02115.