Variably-sized hydropic villi are seen. Although larger hydropic villi can develop cisterns, this particular area does not.
Another image demonstrating large hydropic avascular villi.
Polarized trophoblastic proliferation can be appreciated.
p57 is immunoreactive in the cytotrophoblastic cells and maternal decidual stroma cells.
It is important to keep in mind that the microscopic appearance of decidua and products of conception will vary depending on whether the abortion is spontaneous, missed or therapeutic. In therapeutic abortions, the villi are generally normal, and in missed abortions the villi and decidua may be necrotic and/or hyalinized. Hydropic abortus refers to spontaneous abortions and the rest of this discussion will focus on this topic. The villi in a hydropic abortus will be avascular and edematous. The embryo either never have developed or ceased development very early in gestation, the so-called 'blighted ovum'.1
The pathologist must distinguish between hydropic abortus and molar pregnancies (partial or complete moles) as the latter carries an increased risk of gestational trophoblastic disease. The hydropic villi are not grossly evident in a hydropic abortus, whereas grape-like vesicle edematous villi are usually clearly seen in molar pregnancies.
Microscopic features of a hydropic abortus include: (1) a polar distribution of trophoblasts, orientation toward the placental implantation site - in contrast, molar villi demonstrate circumferential growth of trophoblasts; (2) avascular and hydropic villi that may contain cisterns; (3) Occasionally, irregular scalloped outlines of villi and pseudoinclusions can be seen in both hydropic abortus and partial moles. This finding indicates an abnormal karyotype (remember that most partial moles are triploid), however, a karyotype will be necessary to confirm the chromosomal abnormality.
p57 staining will also be helpful separating a complete mole from a hydropic abortus and partial mole. In the latter two instances, maternal genes are present and expressed, therefore, p57 will be immunoreactive in the cytotrophoblastic cells lining the villi. In a recent study of 13 complete moles, 14 partial moles and 11 hydropic abortus, p57 staining in 10% of the cytotrophoblastic cells strongly favored a partial mole or hydropic abortus. Ploidy was also helpful in conjunction with histologic and p57 findings in separating the three entities (Maggiori). In most instances, a complete mole and hydropic abortus will be diploid and a partial mole will be triploid, another combination (haploid, anueploid, diploid, triploid, tetraploid) can be found in all three entities.1
Typically, hCG level is not elevated (in contrast to complete moles, where hCG levels are very high), and the uterine size is small for dates.
1 Mazur MT, Kurman RJ. Diagnosis of Endometrial Biopsies and Curettings. New York, NY: Springer; 2005: 58-9, 77.
2 Maggiori MS, Peres LC. Morphological, immunohistochemical and chromosome in situ hybridization in the differential diagnosis of Hydatidiform Mole and Hydropic Abortion. Eur J Obstet Gynecol Reprod Biol. 2007 Dec;135(2):170-6. Epub 2007 Jun 28.