Hydatidiform mole

A 29-year-old pregnant woman was found to have a molar pregnancy with a coexistent normal-appearing fetus by ultrasound at 16 weeks. An amniocentesis was performed and revealed a normal karyotype. She presented to the hospital around 20 weeks' gestation with heavy vaginal bleeding. Magnetic resonance imaging was performed for evaluation of depth of invasion of the molar pregnancy. It showed a late second-trimester fetus in a breech presentation. The fetus was displaced toward the right by an enhancing cystic mass compatible with a molar pregnancy. There was no significant deep myometrial involvement. No fetus was seen in the molar sac by ultrasound. The patient presented to the hospital again at 24 weeks, 2 days' gestation with preterm labor and fever. A live male infant was delivered by cesarean section. Molar contents and the placenta were then evacuated from the uterus and submitted to pathology. The patient's previous history was significant for 3 vaginal deliveries and 1 molar pregnancy diagnosed a year previously. One month after delivery, her serum β-human chorionic gonadotropin level remained mildly elevated at 7 U/L (normal range, 0-3 U/L).

The specimen received in surgical pathology consisted of a single placenta, weighing 450 g, and a separate container containing numerous grossly visible vesicles, weighing 370 g. The fetal surface of the placenta was smooth and had 1 attached 3-vessel umbilical cord. The maternal surface showed predominantly normal-appearing cotyledons, with a small area on one side covered by molar vesicles (Figure 1). After careful examination, a dichorionic, diamniotic intervening membrane was identified in the border between the normal placental parenchyma and molar vesicles. Microscopically, a section taken from this border showed normal third-trimester chorionic villi on the left side and molar-type villi on the right side (Figure 2, A; original magnification ×10). No fetal tissue was identified in association with the partial mole. A histologic section of the dichorionic, diamniotic dividing membrane is also shown (Figure 2, B; original magnification ×20). Fluorescence in situ hybridization studies on a paraffin-embedded section of tissue revealed a triploid cell line (XXY), representing the partial molar pregnancy, and coexistent diploid male (XY) cells, representing placental cells from the normal male fetus (Figure 3).

Gestational trophoblastic disease is characterized by neoplastic growth of placental trophoblastic tissue and abnormal fetal-placental development.1 Pregnancies with a hydatidiform mole and a live fetus are extremely rare, arising in about 1 in 20000 to 100 000 pregnancies. Three different mechanisms are possible: a complete mole (diploid, all paternal in origin) coexistent with a normal diploid fetus, a partial mole (triploid, maternal and/or paternal in origin) coexistent with a normal diploid fetus, and a partial mole with an abnormal triploid fetus (both having 69 chromosomes). The first 2 mechanisms represent dizygotic twin pregnancies, and the coexistent fetus has a chance to survive. The third mechanism represents a monozygotic pregnancy, and the coexistent triploid fetus tends to die in the first trimester. The current case was due to the second mechanism, in which one fertilization resulted in a partial hydatidiform mole and the other a normal co-twin. Differential diagnoses include a complete mole coexistent with a normal diploid fetus, and a monozygotic partial hydatidiform mole associated with a live fetus. Morphology of villi and most importantly, karyotypes, help to make the definitive diagnosis.

Recognizing this rare pathologic entity is very important clinically for patient management. It has been proposed that patients with complete hydatidiform mole and coexistent fetus are associated with a considerably higher risk of subsequent development of persistent trophoblastic tumor than a single complete hydatidiform mole.2 However, a more recent study in the United Kingdom showed no significantly increased risk of persistent gestational trophoblastic disease in these patients.3 Partial hydatidiform moles are rarely associated with persistent or metastatic trophoblastic disease, with an estimated risk ranging from 0.5% to 4%. Not enough information has been collected in making a valid prediction for patients with partial mole and coexistent normal fetus due to the rarity of this condition. The presentations can be variable.4 Empirically, pregnancy is allowed to proceed, provided that severe maternal complications are controlled and fetal karyotype and development are normal.

References

1. Altieri A, Franceschi S, Ferlay J, Smith J, La Vecchia C. Epidemiology and aetiology of gestational trophoblastic diseases [review]. Lancet Oncol. 2003;4:670-678.

2. Matsui H, Sekiya S, Hando T, Wake N, Tomoda Y. Hydatidiform mole co-existent with a twin live fetus: a national collaborative study in Japan. Hum Reprod. 2000; 15:608-611.

3. Sebire NJ, Foskett M, Paradinas FJ, et al. Outcome of twin pregnancies with complete hydatidiform mole and healthy co-twin. Lancet. 2002;359: 2165-2166.

4. Nwosu EC, Ferriman E, McCormack MJ, Williams JH, Gosden CM. Partial hydatidiform mole and hypertension associated with a live fetus: variable presentation in two cases. Hum Reprod. 1995;10:2459-2462.

Wenjiang Chu, MD, PhD; Julia Chapman, MD; Diane L. Persons, MD; Fang Fan, MD, PhD

Accepted for publication June 29, 2004.

From the Departments of Pathology and Laboratory Medicine (Drs Chu, Persons, and Fan) and Obstetrics and Cynecology (Dr Chapman), The University of Kansas Medical Center, Kansas City.

The authors have no relevant financial interest in the products or companies described in this article.

Reprints: Fang Fan, MD, PhD, Department of Pathology, The University of Kansas Medical Center, 3901 Rainbow Blvd, Kansas City, KS 66160-7410 (e-mail: ffan@kumc.edu).

Copyright College of American Pathologists Nov 2004
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