22
Molar Pregnancies
797
Hydatidiform Moles and Partial Moles
The term gestational trophoblastic neoplasia (GTN) has become popular in recent years, although it comprises entities that are clearly not neoplastic, such as triploid
“partial” moles. Others commonly now refer to these entities as gestational trophoblastic disease (GTD).
Driscoll (1981), in an excellent review of the morphology of these diseases, strongly favored abandonment of the time-honored term hydatidiform mole. Fox (1989) has added fuel to the fire by suggesting the following: “Is it, in fact, justifiable to continue distinguishing complete from partial moles in routine histopathologic practice?”
He based this opinion primarily on the exceptional finding of a single case of choriocarcinoma said to have followed a partial hydatidiform mole (PHM) (Looi &
Sivanesratnam, 1981). Persisting trophoblastic disease has also been described by Rice et al. (1990). Fox (1997), in analyzing the histologic differences between complete hydatidiform mole (CHM) and PHM, concluded that a degree of subjectivity accompanies these decisions, an opinion with which we strongly agree. Malinowski et al.
(1995) go even further by suggesting a continuum to exist from molar degeneration to choriocarcinoma when they suggested the existence of the “sad fetus syndrome,” the association of a fetus with molar or neoplastic conditions.
This view is not ours, however. After all, choriocarcinoma is also an occasional sequela of an apparently “normal”
gestation, as Fox readily conceded in which there may have been a choriocarcinomatous cell line ab initio.
This chapter discusses the typical hydatidiform mole (the CHM), syncytial endometritis, invasive moles (chorioadenoma destruens), “benign metastasizing mole,” the PHM with or without fetus, and ectopic moles. Their terminology is often confusing and impre- cisely used, but we do not favor abandonment of the term hydatidiform mole. Rather, we implore that it be used more precisely. Choriocarcinoma is discussed in Chapter 23.
Hydatidiform moles are excessively edematous immature placentas, characterized by massive fluid accu- mulation within the villous parenchyma; this fluid charac- teristically leads to the formation of microcysts (cisternae or lacunae) within the villi. In general, there is also an absence of fetal blood vessels. When all villi are thus changed, we speak of a “true” or “complete” mole. When only some villi are involved macroscopically, with large portions of the placenta being grossly more or less normal, then the process is called a “partial” mole. The distinction is often difficult, and strict morphologic guidelines are not easily established. This definition rests, however, on the macroscopic features alone. It can be supported by sub- sequent study or not; the gross description defines the denominational entity. To confuse even more, the distinc- tion is often blurred at early gestational ages, during the evolution of the altered placenta. Because choriocarci- noma (chorionepithelioma) so frequently follows the occurrence of a complete hydatidiform mole, all of these entities are now often encompassed by the term gesta- tional trophoblastic disease. Several comprehensive books have discussed this group of placental diseases (Smalbraak, 1957; Holland & Hreshchyshyn, 1967;
Park, 1971; Goldstein & Berkowitz, 1982; Szulman &
Buchsbaum, 1987; as well as the November 1997 issue of General Diagnostic Pathology). These volumes discuss the evolution of our understanding of the genetic deriva- tion of moles, the frequently confusing terminology, the clinical features, and the therapy of these entities.
Hydatidiform Moles
The CHM is a diffusely edematous and enlarged placenta in which the macroscopically enlarged villi generally lack blood vessels and have cistern-like fluid-filled cavities.
The villi are connected to one another by thin strands of
connective tissue, the former mainstem villi. Intervillous
thrombi occur frequently. Although there is usually no
embryo or identifiable chorionic cavity in CHM, a few
exceptions have been described (Baergen et al., 1996).
The CHM may also occasionally coexist with a normal twin and even triplet pregnancy, but this does not make it a “partial mole.” It can be differentiated genetically as well as macroscopically.
The PHM, which is discussed below in greater detail, is macroscopically composed of normal and distended villi, and it is also more often associated with an embryo or remnants thereof. The trophoblast of complete moles is usually, but not always, more abundant than it is in PHM and in normal placentas. In the CHM there is also frequently much nuclear pleomorphism and anaplasia.
These cellular abnormalities have given rise to several grading classifications, some of which have endeavored to assign prognostic values. Thus, a hydatidiform mole of grade V was considered to have a greater malignant potential than one to which a grade II designation was attached. Hydatidiform moles usually occur as uterine pregnancies, but they are occasionally also present as ectopics in the fallopian tube (Depypere et al., 1993) and ovary. The trophoblast of moles invades the uterus, much like it does in a placenta increta. When hydatid villi and their trophoblast invade the uterus and destroy a portion of it in the process, then this entity is designated an inva- sive mole or a chorioadenoma destruens.
Moles have occasionally been observed to occur repeti- tively, and Parazzini et al. (1991) found that this was much more likely to be the case in patients with CHM. Sand et al. (1984), who reviewed this literature, suggested that it occurred in 0.60% to 2.57% of patients. There were no differences in outcome. Hsu et al. (1963) described five cases of two moles in the same patient; one patient suf- fered three moles. Johnson (1966) observed a patient with four consecutive moles. We have seen a young African- American woman who had three consecutive complete moles; the last developed into a fatal choriocarcinoma. It is of further interest that this patient conceived these moles with two different husbands. Kronfol et al. (1969) described five patients with repetitive moles and commented on the greater frequency of the condition in the Lebanese popu- lation. Patek and Johnson (1978) and Endres (1961) each had a patient with five consecutive hydatidiform moles and no children. Wu (1973) observed a patient with nine consecutive molar pregnancies. Remarkably, all of the moles in the last case lacked Barr bodies, and one was karyotyped as being 46,XY. Although the author specu- lated on a paternal cause for this repetitive event, normal paternal and maternal karyotypes were found. Semen analysis was refused. Ambrani et al. (1980) reported famil- ial moles in three family trees, but the possible genetic cause was not determined. Parazzini et al. (1984) found two sisters, one with three CHMs and the other with one.
La Vecchia et al. (1982) described monozygotic twins, each with molar pregnancy. Most recently, Slim et al. (2005) have analyzed familial moles genetically. They studied a
family in which five women had seven moles, three miscar- riages, and three children. Their conclusion was that a previously linked locus to 19q13.4 was not responsible and that other factors modulate the occurrence of moles. An important genetic study of the origin of two choriocarci- nomas was undertaken by Osada et al. (1991). They exam- ined the restriction fragment length (RFL) polymorphism of the moles and preceding pregnancies in two patients. In one family the choriocarcinoma could be traced to a previ- ous complete, androgenetic hydatidiform mole, not the two normal pregnancies. In the other patient, however, the tumor derived from the third of three normal pregnancies and carried both parental chromosomal markers. The pub- lication does not provide details whether one or the other genome had a better prognosis. The few similar reports in the literature are referred to by these authors. Since then, Seoud et al. (1995) evaluated the familial recurrent moles (13 moles in the pedigree) of two sisters with moles and found a high degree of unusual lymphocyte antigen histo- compatibility. Studies of this kind should probably now be employed to better understand the genetic reasons for molar gestations and to correlate choriocarcinoma with putative precursors. Such an effort is especially important when long time spans separate pregnancy and tumor, or when primary choriocarcinomas of presumably nongesta- tional types are observed, for example, the cervical lesion reported by Ben-Chetrit et al. (1990). We have seen a placenta of a near-term gestation with surviving, normal female infant and a sharp division between a molar portion and normal placental tissue (Fig. 22.1). Flow cytometry on the molar portion showed it to be uniformly tetraploid, and the normal tissue was diploid. DNA was isolated from paraffin-embedded tissue and polymerase chain reaction (PCR) studies were then undertaken. Employing five dif- ferent markers, all RFLs were uniform, assuring with highest probability the identical genotype of the tissues.
There was one chorionic sac and no second cavity or embryonic remnant. Remarkably, many hydatid, tetra- ploid villi had fetal blood vessels, some atrophied, and others well circulated by the living infant. We interpreted this specimen as having one of two possible origins. Either a focus of placental tissue underwent polyploidization (unlikely), or a monozygotic, monochorionic twin devel- oped as tetraploid fetus (and died), leaving behind the mole. Meanwhile, the other twin’s circulation kept perfus- ing some of the molar villous tissue. Although the gross impression was initially of a partial mole, the studies ruled this out, as did the presence of a normal surviving infant.
Follow-up study showed no untoward sequelae (Benirschke
et al., 2000). Higashino et al. (1999) described triplets, two
normal fetuses (46,XX and 46,XY) and normal placentas
and a typical androgenetic mole (46,XY), that were
followed by persistent trophoblastic disease. They were
totally separate placentas, however, in contrast to the case
described by us.
Figure 22.1. A: Sharp division of molar (top) and normal pla- cental tissue (bottom) in presumed monozygotic (MZ) twin.
Molar tissue is tetraploid, diploid female infant survived. B:
Focal intermingling of molar with normal villi. C: Molar vesicle
with atrophying blood vessel. D: Molar villus with intact, per- fused fetal blood vessel. Note tetraploid connective tissue of mole. H&E ¥16 (A), ¥16 (B), ¥64 (C), ¥160 (D).
The natural history of recurrent molar disease was dis- cussed by Federschneider et al. (1980) in their presenta- tion of seven patients. They also reviewed the literature and stated that their recurrent cases were more malig- nant and more often required treatment for residual disease than nonrecurrent moles (see also Rice et al., 1989). Mor-Joseph and his colleagues (1985) reported four recurrent moles following three spontaneous abor- tions. The moles occurred after clomiphene therapy, as was previously described by Schneider and Waxman (1972). These experiences support the finding by Paraz- zini et al. (1985) that moles are significantly more common with increasing numbers of spontaneous abortion. An interesting case with three recurrent CHMs was described by Fisher et al. (2000a). All three were biparental (not androgenetic), yet CHMs; moreover, the male partners were two different individuals and two moles were XX, one was XY. This finding has implications for possible in vitro fertilization (IVF) efforts in patients with recurrent moles. Helwani et al. (1999) had also described CHM with biparental origin in the seven (!) moles from two Lebanese sisters. The authors suggested the existence of an autosomal-recessive gene that was responsible. In a subsequent publication, Moglabey et al. (1999) studied members of these two families and identified an aberrant gene on 19q. Most interestingly, Sensi et al. (2000) found in an unrelated Italian family with recurrent moles of biparental nature (!) an abnormality of 19q in two sisters.
Fisher et al. (2004b) reviewed the entire topic of recur- rent moles (152 pregnancies) and stated that the sequelae were similar to the usual CHMs. It is thought that this abnormal gene is involved in imprinting and thus sup- presses the usual influence of the maternal gene, causing enhanced expression of the paternal allele. In this way, a molar phenotype would be expressed even though the mole was biparental. Not only is the genetic derivation of complete moles unusual (most have only paternal chro- mosomes, that is, are “androgenetic”), but there is great variation in the prevalence of moles in different popula- tions. Asian women, especially Japanese and Filipinas, suffer a much-increased frequency of molar pregnancies.
It is further remarkable that hydatidiform moles have been observed only in human pregnancies; only one other primate has exhibited this pathology despite extensive breeding records. This was a mole occurring in a chim- panzee reported by Debyser et al. (1993). This Pan trog- lody tes , while pregnant, died from massive genital hemorrhage and ovarian torsion. The entire uterus was filled with a PHM that had commonly accepted histologic features. Its DNA content was hyperdiploid, possibly trip- loid, and a degenerated fetus was present. There are rare reports of moles in cows (Folger, 1934), and Drieux and Thiéry (1948) reviewed rare cases described in a cat and dog. These are truly exceptional circumstances and their analogy to human CHM is uncertain. This was the case
until Meinecke et al. (2002) presented their specimen of a typical hydatidiform mole in cattle that was associated with a stillborn male calf. They also reviewed the few previously reported cases of moles in animals. For the first time it was conclusively shown that the 60,XX molar tissue was indeed androgenetic and the co-twin calf was 60,XY. There were rare chimeric cells in the two tissues that derived most likely from the formerly present pla- cental anastomoses, but the term (that includes freemar- tin) is strictly speaking incorrect, as the normal fetus was male. Apparently there were no sequelae to the cow that delivered the twins. Choriocarcinoma is also exception- ally uncommon in animals, although it has been reported in a rhesus monkeys (Chapter 23).
Incidence
The exact incidence of hydatidiform moles varies in dif- ferent populations and it is impossible to ascertain it exactly. An estimate of 1 per 2000 pregnancies is gener- ally cited for the United States (Hertig, 1950). When Grimes (1984) undertook an extensive epidemiologic study of many different populations he found an CHM incidence of 1 in 1000 pregnancies for the general U.S.
population. Etiologic factors were not obtained from his
investigation. In part, the inability to ascertain a precise
incidence is due to the probable confusion of CHM with
PHMs, the presumed triploid conceptuses. Undoubtedly
also, PHMs have often been counted as CHMs (the pre-
sumed androgenetic moles), especially when one reviews
the early literature. We know from personal experience
that this is still the case. The methodologic problems in
ascertaining a true incidence have been dealt with par-
ticularly well by Buckley (1987), and the later contribu-
tion by di Cintio et al. (1997) is relevant. In their review
of the epidemiology of gestational trophoblastic disease
they found that the incidence in the U.S. is 108/100,000
pregnancies, whereas in Northern Italy it was only
62/100,000. In Indonesia it was 993/100,000, whereas in
China it was 667/100,000 pregnancies. There is then little
doubt that vast differences in frequency of CHM and
other GTDs exist; CHM is especially common in the
populations of Hawaii, the Philippines, and Japan. Table
22.1 summarizes incidence figures derived from several
relevant studies. Other tables may be found in these pub-
lications and in the books cited. Several authors have
provided additional reviews of early incidence figures
that add little important information. There is thus a
general agreement that the incidence of moles is, at least
partially, racially influenced. This phenomenon is not
completely explicable by the higher parity and older age
of Asian gravidas (Iverson et al., 1959). Das (1938) found
moles more commonly in the Indian than the Caucasian
population. In an inquiry that distinguishes environmen-
tal from racial causes, Natoli and Rashad (1972) observed
moles much more often in the Japanese and Hawaiian stock, than in Chinese and Caucasian residents of Hawaii;
many other examples of racial influences can be found in the cited publications. It must also be recognized that postmenopausal women are not necessarily free from the possibility of conceiving a molar gestation. Over 100 cases of moles past age 50 have been described, and Garcia et al. (2004), who reviewed the topic, even found a 61-year-old woman with this disease. She recovered after evacuation.
These reports all found that the incidence of CHM correlated with race rather than with geography. A review of molar pregnancy suggested also that the traditional clinical picture presented by patients with moles has changed, but that persistent trophoblastic disease has become more common (Soto-Wright et al., 1995). Bracken (1987) undertook a special study of these features and found that the incidence of CHM in Japanese was inex- plicably twofold higher than that of Caucasians and Chinese. He stated, “Maternal age is the most consis- tently demonstrated risk factor; teenagers and, especially, women over age 35 being at increased risk” (see also Bandy et al., 1984).
Maudsley and Robertson (1965), who described the development of a mole in a 52-year-old woman, reviewed the literature of approximately 60 similar cases in older women. Mathieu (1939) made a thorough review of moles and choriocarcinomas and found a 55-year-old woman, emphasizing the dependency on maternal age. Clearly, older maternal age (and somewhat also extremely young age) predisposes to GTDs (di Cintio et al., 1997). The possible influence of the father’s age has also been studied.
No relationship was ascertained in most studies, except in that undertaken by La Vecchia et al. (1984), who found a higher incidence in fathers over 45 years, and this pre- dilection was compounded by smoking. Other investiga- tors have not identified smoking as a risk factor. The possible and disputed etiologic role of herbicides is unlikely to be resolved, according to Bracken (1987).
McCorriston (1968) evaluated possible reasons for the higher incidence in particular racial groups of Hawaii and stated that their different food preferences are unlikely etiologic antecedents. This point was further examined in a case-control study from China where no relation to diet was identified by Brinton et al. (1989). Berkowitz et al.
(1985a) suggested that vitamin A deficiency may be caus- ally related to molar gestations, and suggested carotene supplements for prevention. There have been no other meaningful concepts that explain the racial differences of CHMs. Indeed, the possibility has been studied that the marked ethnic differences in molar incidence reflect different diets, and possibly other environmental factors might disappear upon immigration to other countries. A key question thus is whether the incidence of CHM in Asians who emigrated to San Francisco and then lived Western lifestyles differs from that of Caucasians. Over- street (personal communication, 1963) ascertained that, in the immigrant Asian population of San Francisco, the incidence of CHM is 1 per 2000 deliveries, much the same as in Caucasian women. Atrash et al. (1986) similarly ascertained molar pregnancies among 84,318 abortions from different institutions. The incidence of moles was 7.5 per 10,000 pregnancies (1 per 1333). Bracken (1988), however, has criticized this result on methodologic grounds and as being a gross underestimate. Although more moles were found in Chinese, this difference was not significant. African Americans had the same inci- dence as whites. The only significant correlation occurred with maternal age.
A number of classifications of GTDs should be men- tioned. The World Health Organization (WHO) recog- nizes the following scheme (Tavasolli & Devilee, 2003):
Hydatidiform mole Complete mole Partial mole Invasive mole Metastatic mole
Table 22.1. Incidence of complete hydatidiform moles in various populationsCountry Author Year Time span of the study Incidence/term gestation
India Das 1938 108,951 gestations 1 : 502
Mexico Márquez-Monter 1963 1961 gestations 1 : 200
Hong Kong Chun et al. 1964 1953–1961 gestations 1 : 242
Sweden Ringertz 1970 1958–1965 gestations 1 : 1560
Singapore Teoh 1971 1963–1965 gestations 1 : 823
Israel Matalon 1972 1950–1965 gestations 1 : 1300
Hawaii Natoli 1972 1950–1970 gestations 1 : 977
Paraguay Rolon 1977 1960–1969 gestations 1 : 4369
Paraguay Rolon et al. 1990 1970–1982 gestations 1 : 3906
Netherlands Franke 1983a 1978–1980 gestations 1 : 2270
Italy Mazzanti 1986 1979–1982 gestations 1 : 1510
England Bagshawe 1986 1973–1983 gestations 1 : 1000 to 1.54 : 1000
Trophoblastic neoplasms Choriocarcinoma
Placental site trophoblastic tumor Epithelioid trophoblastic tumor
Nonneoplastic, nonmolar trophoblastic lesions Placental site nodule and plaque
Exaggerated placental site
The International Federation of Gynecology and Obstetrics (FIGO) and the National Institutes of Health (NIH) use different systems for classification, and prog- nostic scores were assigned by the classification issued from the WHO. These aspects and histologic criteria are well covered by Horn and Bilek (1997).
Genetics
Ever since Park’s early studies (1957), cytogeneticists have known that sex determination of trophoblastic tumors appeared to be impossible. Shorofsky (1960), applying cytometrics, found that nuclei of molar tropho- blast had the same parameters as normal trophoblast.
Márquez-Monter (1966), using radioautography, showed that the syncytium of molar trophoblast originates from cytotrophoblastic precursors, just as it does in normal villi. With the discovery of the sex chromatin, it became known that most moles possess a Barr body (sex chroma- tin: the inactivated X chromosome of females) (see Tominaga & Page, 1966; Baggish et al., 1968; Loke, 1969).
Early systematic studies by Sasaki et al. (1962) had also shown that most hydatidiform moles possessed an appar- ently normal female or occasionally male diploid comple- ment. Bourgoin et al. (1965a,b) also found male and female karyotypes but further observed some aneuploidy in their specimens. They encountered methodologic dif- ficulties in making cell preparations, however. Sajiri Makino and his colleagues in Japan (1964, 1965) ascer- tained that some apparent hydatidiform moles, now referred to as partial moles, have a triploid chromosomal constitution, an observation that was soon confirmed by Carr (1969). It is now known that triploidy is the karyo- type of most PHMs.
The major breakthrough in our understanding of molar pregnancies came when Kajii and Ohama (1977) showed that hydatidiform moles are “androgenetic,” that is to say, all molar chromosomes are paternally derived. It is easiest to envisage that this occurs as the result of fertilization of an “empty egg,” with subsequent duplication of the haploid spermatozoal complement. That mechanism also explains why moles are almost always 46,XX. If a male- determining spermatozoon with Y chromosome were to fertilize an empty egg, a karyotype of 46,YY would result from such sperm duplication, and this is apparently a lethal cellular condition. It must be mentioned, however, that nobody has shown an “empty egg” as yet in ovaries
or ovulated follicles. Thus, it may be possible that chro- mosomal or other nuclear abnormalities predispose to the female component’s regression. The theoretical aspects of this vexing problem have been discussed at great length by Golubovsky (2003), a paper worth reading as it also attempts to explain twins and chimeras in these products of gestation. Kajii and Ohama karyotyped 20 moles and determined the disposition of the chromo- somal Q- and R-band polymorphism. There is sufficient heterogeneity in the normal human chromosome struc- tures that this polymorphism allowed them to ascertain with confidence that, in CHM, these markers were exclu- sively paternal (Fig. 22.2). These findings were quickly confirmed by Wake et al. (1978a) and Jacobs et al. (1978), and Azuma et al. (1991) showed that the molar mitochon- drial DNA has a maternal origin. Many markers are now available for chromosome identification. They extend from the Q and R bands to C bands, shown by fluorescent in situ hybridization (FISH), and they also include the identification of inversions, translocations, and other minor varieties, as shown in Figure 22.2. Since this origi- nal description of androgenicity, not only has the concept been amply confirmed, but androgenesis has also been verified by genetic markers, such as homozygosity of polymorphic enzymes (Jacobs et al., 1980) and human leukocyte antigen (HLA) markers (Wake et al., 1978b;
Couillin et al., 1985; Goldman-Whol et al., 2001). Interest- ingly, two of the mothers studied by Kajii and Ohama (1977) had reciprocal translocations of different chromo- somes. Similar findings were then made in the later studies of Lawler et al. (1979) and Vejerslev et al. (1987d). This apparent frequency of translocations might initially be assumed to have possible etiologic significance for the creation of an empty egg, but subsequent studies have negated this possibility. Vejerslev et al. (1987d) karyo- typed 237 mothers and 217 fathers of CHM as well as 125 mothers and 106 fathers of PHM. “No significant increase in the frequency of translocations . . . was found.”
To explain the genesis of moles, it is further hypothe- sized that molar transformation of the conceptus results from the homozygous concentration of some lethal genes.
It is commonly estimated that four or five lethal genes are
regularly carried (in the heterozygous state) in normal
individuals. When they become homozygous (as they
would be in CHM), the duplication of lethal genes causes
embryonic death; only the placenta survives, to be trans-
formed into molar vesicles. The notion of an empty egg
with fertilization by a 23,X sperm and subsequent chro-
mosomal duplication was supported by the genetic studies
of Jacobs et al. (1980). Moreover, experimental investiga-
tions in mice indicated that maternal and paternal
genomes are essential for normal embryonic and placen-
tal development. Paternal genes are apparently especially
important for normal placenta formation. It was found
that embryos from two female pronuclei (gynogenesis)
developed poorly, and particularly their placental mem- branes were abnormal. The embryos derived from two male pronuclei died very early, but their placentas were reasonably well formed (Surani & Barton, 1983; Barton et al., 1984; Ho et al., 1984). Irregular X-chromosome inactivation inexplicably also occurs in placental mem- branes of female conceptuses. There is preferential female X-chromosome activity in a variety of cells of the placenta of female fetuses (Tagaki & Sasaki, 1975; Roper et al., 1978; Harrison & Warburton, 1986; Harrison, 1989).
After this definition of androgenesis as the cause of molar development had been clarified, many cytogenetic studies were performed on CHMs and PHMs to further delineate the possible relations of chromosome sets and the possible impact on the prognosis of the various molar conceptions. Tsuji et al. (1981) determined that there is a higher frequency of aneuploidy (2n = >46) in the moles from older women, and also in invasive moles and in choriocarcinomas. They suggested that it may have prog- nostic significance. Jacobs et al. (1978) had also observed an apparently malignant mole with aneuploidy and hypo- tetraploidy but with a paternal origin of all chromosomes.
When trophoblastic cells are separated from molar tissue and then cultured, Habibian and Surti (1987) found that these cells exhibit a 2.8 times greater frequency of poly- ploidy when compared to normal trophoblast. Chromo- somal breakage was also much more common. The X-chromosomal replication pattern of diploid, androge- netic molar cells, however, was normal (Tsukahara &
Kajii, 1985). A useful review may be found in the paper of Lindor et al. (1992). The participation of imprinting and of telomerase activity in moles was reviewed by Li et al. (2002). Castrillo et al. (2001) had shown that the imprinted gene product p57
KIP2is paternally imprinted, and that it was absent or markedly underexpressed in cytotrophoblast and mesenchyme of CHMs because of their paternal derivation, while decidua, PHMs, and normal placentas had good expression. This proves to be a potentially useful additional means of differentiation between the moles, and an immunohistochemical stain has been developed and used successfully (Jun et al., 2003). In a later study, however, Fisher et al. (2004b) showed paradoxical gene expression due to retention of a maternal copy of chromosome 11 (plus two paternal copies) in a case of CHM, thus explaining the rare abnor- mal expression of this gene in marker studies for p57
KIP2. Fukunaga (2004) found aberrant expression of p57
KIP2in two tetraploid (92,XXYY) moles. This suggests deriva- tion from two sets of chromosomes, paternal and mater- nal. Saxena et al. (2003) showed that the IPL gene (also imprinted) is absent from the syncytium in moles. It is also of interest to note that N.J. Sebire et al. (2004), employing this stain on choriocarcinomas, were unable to infer their origin.
As more moles were investigated genetically, excep- tions to the early findings have come to light. The exis- tence of 46,XY moles was then first recognized (Surti et al., 1979; Ohama et al., 1981; Pattillo et al., 1981; Surti
Figure 22.2. Normal human diploid karyotype, 46,XY,Q-banded (Q = quinacrine). In the normal karyotype, chromosomes may be banded by different techniques.
Here, a normal male set is banded with quinacrine stain (Q bands), which allows precise comparison between elements (maternal and paternal). Note that in this male there are differences between the banding pattern of several elements. Various segments do not “match”; they represent normal variations in our chromosomes that are inherited. The following chromosomes differ in this karyotype: No. 1, the right element has additional hetero- chromatin at the centromere; No. 9, the left element has additional centromeric heterochromatin, and the right chromosome has an inversion; No. 14, there are promi- nent satellites; No. 15, the right chromosome has a cen- tromeric variant; No. 16, the right chromosome has additional centromeric material; No. 22, the left chromo- some has prominent satellites, and the right chromosome has a centromeric variant. It has been possible to show that, in the typical complete hydatidiform mole (CHM), there is only the banding profile of the paternal chromo- some set, both elements are exactly alike (Kajii & Ohama, 1977). (Courtesy of Dr. Mark Bogart, Honolulu.)
et al., 1982). Fisher and Lawler (1984) found three 46,XY moles and determined that they derived from dispermy.
It now appears that about 8% of CHMs are the result of fusion of two male pronuclei following dispermic fertil- ization (Ford et al., 1986). In addition to the XY moles, occasional heterozygous 46,XX moles were found (approximately 5% to 10% of moles are now known to be heterozygous and androgenetic). Wake et al. (1981) suggested that these moles may have a greater malignant potential. Kajii et al. (1984) studied nine XY moles and compared the clinical outcome with 16 normal XX moles.
Their study showed dispermy as the causal mechanism in the XY moles. Three of eight XY moles and five of 15 XX moles had a delayed decrease in human chorionic gonadotropin (hCG) titers. Mutter et al. (1993) were unable to show that an increased risk for metastasis exists in the XY moles that they studied with PCR. They found 7.7% of the moles with metastatic consequence and 9.1%
of the metastatic group in their large sample of moles studied possessed a Y chromosome. In the experience of Fisher and Lawler (1984), patients with heterozygous moles needed further treatment of trophoblastic tumor in 31%. In a subsequent study of this important observa- tion, Lawler and Fisher (1987) examined 163 moles, 38 (23%) of which were PMHs and 125 were CHMs. All of the PHM were either triploid or hypertriploid, with most having arisen by dispermic fertilization; they had no untoward sequelae. Of the CHM, whose genetic study was informative, 10% were heterozygous diploid moles.
Of these heterozygous moles, 25% required subsequent chemotherapy, in contrast to 17.6% of the CHMs with homozygous constitution, a result that was not statisti- cally significant.
Hitchcock et al. (1991) addressed the difficult differen- tial diagnosis between CHM and PHM when they under- took an important retrospective flow cytometric study of molar specimens diagnosed at the Armed Forces Institute of Pathology (AFIP). Their diagnosis of CHM differed from that of the submitting pathologist in 78%, and in the diagnosis of PHM in 57% of cases. Howat et al. (1993) evaluated the pathologist’s ability to reliably distinguish between these conditions and provided spe- cific criteria. The findings of an evaluation of 50 molar pregnancies by seven competent pathologists gave no assurance of a correct diagnosis. Fukunaga et al. (1996) found by employing flow cytometry on paraffin- embedded tissues of 35 hydropic villi that 25 were complete hydatidiform moles, while 10 were hydropic abortions; none were partial moles. Ten hydropic abor- tions were of maternal and paternal contributions, with two being tetraploid. Two tetraploid moles developed invasive lesions, one a choriocarcinoma. They suggested that tetraploid moles require special follow-up and strongly advocated the use of DNA determination of moles (see also Fukunaga et al., 1993). Lage (1991) deter-
mined that one course of single-agent chemotherapy caused complete remission in all triploid PHMs, and more were required in the two diploid PHM they studied.
Later, these authors examined 142 hydropic placentas (Lage et al., 1992) and found 38% CHM, 35% PHM, and 26% hydropic abortuses, the majority of the latter being near diploid; only 11% were triploid. “Persistent tumor”
was seen in 33% of CHM and 12% of PHM. Additional insight has been gained through the publications by van de Kaa and her colleagues (1991, 1993, 1997), who are strong advocates for a genetic/ploidy study to objectively differentiate CHM from PHM and hydropic abortuses.
Berezowsky et al. (1995) found a high proportion (42%) of nonmolar and molar (47%) conceptuses in their DNA study, while most partial moles (89%) were triploid.
They suggested that tetraploid moles derive from diploid conceptions with subsequent polyploidization.
From these studies, then, it appears that it is not yet possible to reliably diagnose the molar pregnancies by hematoxylin and eosin (H&E) histologic study alone, let alone assign a prognosis on the basis of a CHM karyo- type. Others have come to the same conclusion and strongly urge cytometry to be part of the evaluation (Conran et al., 1993). The most important decision to be made when encountering a mole is to differentiate between triploidy and diploidy, for which flow cytometry is the most important methodology whose usage should be more widely employed. The patients with PHMs never experienced metastatic disease. Only rarely have such patients required chemotherapy for persistent tropho- blast, and we doubt that it was needed in many cases;
moreover, the diagnosis may be in error or is poorly sup- ported, as was the case in the patient recorded by Gardner and Lage (1992). Bae and Kim (1999) showed that the possession of telomerase activity of CHM is more likely to eventuate in persistent trophoblastic disease. In recent years, however, pathologists have added new tools to their armamentarium in order to distinguish CHMs from PHMs and hydropic abortuses. This was especially well accomplished by antibody staining for p57.
Although the gross morphology alone of PHM is often
persuasive, difficult cases do arise, especially when twin
pregnancies are admixed with moles. The existence of
confined placental mosaicism (CPM) has been evoked to
explain unusual cases. Thus, Sarno et al. (1993) described
a partial mole (69,XXX) associated with a surviving
diploid premature girl. We saw the placental material
from a triploid conceptus born at 33 weeks and who sur-
vived for some time without anomalies (C. Kaplan, per-
sonal communication). The placenta of this 2050-g boy
was a 1000-g placenta with chorangiosis but without
hydatid changes. As has been alluded to earlier, because
cytogenetic studies are not feasible for all laboratories,
it has been strongly advocated that ploidy of moles be
determined by the rapid method of flow cytometry
(Anonymous, 1987; Benirschke, 1989). Fisher et al. (1987) showed early on that this technique unequivocally distin- guishes the two molar entities. The same method was employed by Hemming et al. (1987), who demonstrated that CHMs more often had hyperdiploid cells. Lage et al.
(1988) also produced similarly good results in separating CHMs from PHMs with this method (Fig. 22.3). It is noteworthy that paraffin-embedded material can be used for retrospective flow cytometric studies. Bell et al. (1989, 1998) recommended such studies and PCR for more dif- ficult cases. Moreover, because flow cytometry easily dis- tinguishes diploid complete moles from triploid partial moles, it is important to note that occasional and unex- pected findings occur that further mandate employment of this methodology. As an example, Lage et al. (1989) found three tetraploid moles. One of them, a 92,XXXX mole, was a CHM. Another specimen had a complement of 92,XXYY (two paternal and two maternal genomes), and one was diploid/triploid mosaic (69,XXY/90,XXXY).
After evacuation, none of these moles had recurrent tro- phoblastic disease. Martin et al. (1989) also determined the ploidy of various moles from paraffin blocks, as in the study of Hitchcock et al. (1991) reviewed above. The outcome for the patients following delivery of the moles was known. It was found that moles with an aneuploid population of cells had a significantly higher incidence of gestational neoplastic sequelae than did those with diploid (euploid) moles. Although these malignant” moles also had a higher proliferative index, this was not statistically significant. A retrospective study of 13 complete moles by Bewtra et al. (1997) identified eight (61.5%) as being tetraploid, and diploid moles often had tetraploid cells as well. None developed sequelae and no histologic differ- ences were found in these populations. Tetraploid moles tended to occur in older patients and were accompanied by higher b-hCG levels. Newer technology employs DNA fingerprinting from very small samples to differentiate these conditions (Nobunaga et al., 1990; Ko et al., 1991);
also, PCR is advocated for rapid diagnosis (Fisher &
Newlands, 1993). Ishii et al. (1998) advocated the use of short tandem repeat-derived DNA polymorphism for the differential diagnosis of twins with moles and partial moles with fetus. Lai et al. (2004) had to reclassify some specimens when they examined moles by fluorescent mic- rosatellite genotyping and ploidy study by in situ hybrid- ization. They found that the diagnosis of CHM was more readily done histologically than that of PHM. Three PHMs developed GTDs, but the authors did not define their nature.
Mixed populations of cells with different karyotypes occur in the occasional exceptional CHM. Takagi et al.
(1969) described a triploid/diploid “mosaic” XX mole without providing further relevant information. Ford et al. (1986) found an avascular, androgenetic diploid CHM (608 g) that was mosaic for normally fertilized cells.
Interestingly, there was a reciprocal translocation in one population that enhanced the ease of analysis of the chro- mosomal origins. To explain their finding, the authors suggested that the fusion of dizygotic (DZ) twins was unlikely; they favored an origin from the abnormal fertilization of a single egg. In our interpretation, fusion of two DZ twins (a chimera) remains a strong possibility.
The case also argues strongly against the perhaps overly simplistic notion that moles result from fertilization of an empty egg. The authors urged that other diploid moles be examined for possible differentiation of mosaicism/
chimerism. Vejerslev et al. (1987a) found two homozy- gous moles with second cell lines that also suggested twin gestations. Other possible admixtures of fraternal twins, one a mole and the other normal, are discussed below.
Vejerslev et al. (1987c) have summarized all unusual karyotypes of CHM, diploid PHM, and the hyperdiploid CHM. In recent studies of our own service, a PHM was found in a specimen whose amniocentesis showed uniform
Figure 22.3. DNA histogram of normal placenta (above), acomplete mole (center), and a triploid partial mole (below). The vertical axis is the number of cells; the horizontal axis is fluo- rescence and indicates DNA content. There is a single diploid peak in the normal placenta, a large diploid peak in the CHM with a minor peak at tetraploidy, and a large peak of triploid cells (arrow) in the partial mole. (Source: Lage et al., 1988, with permission.)
trisomy 3 and whose aborted fetus had the characteristic features of this trisomy.
Among other exceptional karyotypes there are exist the tetraploid specimens. Vejerslev et al. (1987b) found one tetraploid mole with three paternal contributions and one maternal contribution among 29 molar concep- tuses, 24 of which were dispermic triploids. This tetraploid specimen was, in principle, similar to the PHM but did not have the clinical presentation of that entity. Lage et al. (1989) identified three tetraploid moles. One of them, a CHM, had 92,XXXX; the two PHMs had 92,XXYY and 90,XXXY,-11,-13/69,XXY, respectively, reason for these authors to strongly advocate the use of flow cytometry for identification of unusual specimens. It now appears that most diploid moles have also some tet- raploid peaks at flow cytometric study; those with diploid genomes occurred in younger women (Bewtra et al., 1997). The newer diagnostic methods of genetic analysis already referred to may be just as rapid in appropriately equipped laboratories, and they are decisive. Saji et al.
(1989) showed elegantly by DNA fingerprinting that CHMs have only paternal genes. The advantage of such a study with restriction fragment length polymorphism (RFLP) is that only minute samples are required. When RFLP studies of trophoblast and corresponding fetuses were compared in 50 samples, four pairs showed differ- ences in DNA content (Butler et al., 1988). This unex- pected finding has not yet been fully explained, but it is likely to be important.
Morphology
A “hydatidiform mole is defined as a conceptus, usually devoid of an intact fetus, in which all or many of the chorionic villi show (1) gross nodular swelling culminat-
ing in cyst formation, (2) disintegration of blood vessels, and (3) variable proliferation of trophoblast” (Edmonds, 1959). This must be regarded as the swelling of most or all of the villi in a placenta that may once have been more normal. When moles are diagnosed in the course of a pregnancy, the molar tissue fills most of the uterine cavity (Fig. 22.4). Intervillous coagula are common because of the aberrant intervillous circulation, and it may be associ- ated with vaginal bleeding. Moles occasionally present with the clinical picture of abruptio placentae, according to Sauter (1965). The uterus may be markedly distended and may even rupture, especially when it is stimulated to contract (Lee & Siegel, 1965). Ovarian theca lutein cysts are often present (Fig. 22.4) because of the ovarian over- stimulation by the excessive hCG production. Because the ovarian cysts regress spontaneously after evacuation of the mole, the ovaries do not need to be removed when hysterectomy is performed for molar sequelae.
The molar villi are fairly uniformly distended by fluid.
McKay et al. (1955a,b) have analyzed this fluid biochemi- cally and found its osmolality to be lower than that of maternal serum. The authors suggested that later gesta- tional trophoblast has different capacities, which they explained as a reason why villi atrophy rather than expand when fetal death occurs in later fetal life. Jauniaux et al.
(1998), who also reviewed subsequent studies, compared the content of molar vesicles with nuchal fluid, amnionic fluid, and maternal serum. They found significantly lower urea content and determined that the vesicle fluid a- fetoprotein was more yolk sac–like, whereas nuchal fluid was more liver-like. When molar tissue is floated in water (Fig. 22.5), the translucent nature of the distended termi- nal villi is evident. The protein content of the fluid is apparent when such villi are first fixed and then floated (Fig. 22.6). The connections to a possible former chorionic
Figure 22.4. Hydatidiform mole in situ. Note the distention of the uterus and bilateral theca lutein cysts of ovaries. The vesicular nature of molar villi is apparent.
sac also then become evident. The swelling is primarily one of the terminal villi and can be construed to result from the continued water transport by trophoblast. The syncytium has this singular transport function. In the absence of fetal vessels to remove the transported fluid, the villi expand, and enlarged cisternae develop in the villi and vacuoles in the syncytial cytoplasm. The absence of a fetus, the lack of a chorionic cavity, and deficiency of chorionic vasculature are characteristic of CHM. Never- theless, a few cases with tiny embryos have been described.
Thus, Hertig (1968) depicted a chorionic cavity in the center of an apparently complete mole that was fixed in situ within a uterus (his Figure 196). This chorionic sac contained a deformed, stunted embryo with this mole (his Figure 199). Because an embryo was associated with the specimen, it may be argued in retrospect that the speci- men was a PHM. This consideration is invalidated by the case shown in Figure 22.7. In this patient, a tiny embryo was present within a typical hydatidiform mole (the patient’s third). This pregnancy was followed by fatal,
disseminated choriocarcinoma. Baergen et al. (1996) showed that a hydatidiform mole (androgenetic) had a
“fetal pole” and a gestational sac at early sonography. In fact, Weaver et al. (2000) even showed that the occasional amnion that can thus be found in verified CHM has an androgenetic pattern. Several authors have found that fetal red blood cells and other fetal structures occur in verified CHMs and that the usually avascular villi may possess capillaries early in development (Fisher et al., 1997; Paradinas et al., 1997; Qiao et al., 1997; Zaragoza et al., 1997; Neudeck et al., 2003). Thus, occasional embryos accompany moles, especially perhaps during their earliest development. This is an important point as pathologists often rely solely on microscopic features for the differen- tial diagnosis and these do not necessarily conform to the teaching they received. This point should have been evident from the presence of connective tissue in the villi alone. As was discussed in some detail in Chapter 12, the connective tissue of the placenta has an embry onic derivation; it does not come from the trophoblastic shell, as was formerly thought. That the differential diagnosis
Figure 22.5. Hydatidiform molar villi photographed underwater. Note the bulbous swelling of terminal villi and the slender nature of mainstem villi.
Figure 22.6. Same villi as in Figure 22.5 but after fixation in Bouin’s fixative. The protein has precipitated, making the villi opaque. The connecting stalks are obvious.
between the three categories—hydropic abortus, PHM, and CHM—is difficult on histologic grounds alone was well demonstrated by Gschwendtner et al. (1998). They studied, retrospectively, their “molar” specimens with ploidy analysis. This was done after the stricter criteria proposed by Paradinas (1994) had been applied. Despite this special care, ploidy study necessitated reclassification in many cases. This aspect has also been studied by Genest (2001). Agreement was found in histology and ploidy results with CHM, and in 79% of PHM and triploidy.
Their discussion indicates, however, that completely reli- able histologic features do not exist that allow accurate categorization; ploidy study is required, especially in gestationally young specimens.
Moles are now typically removed by suction curettage.
Because the specimens are usually markedly disrupted and accompanied by much clot, it is not surprising that possible chorionic sacs and embryos are not found more often. The stalks from which the hydatid villi emanate, however, also indicate that a more normal structure must have preceded the typical CHM configuration. Also, in younger CHMs, there is generally less villous swelling, and the connections to a possible chorionic sac by stem villi are more visible (Fig. 22.8). Kajii et al. (1984), more- over, found that younger moles had smaller, elliptic or club-shaped villi and poorly delineated cisternae, whereas older moles had more globular villi (see also Keep et al., 1996). The latter also had more trophoblastic hyperplasia and fewer remnants of capillaries; no signifi - cant morphologic differences were found between XY and XX moles.
It is of historical interest to cite the invasive mole described by Jarotzky and Waldeyer (1868). They observed a chorionic cavity in the center of this typical invasive mole whence all the hydropic villi emanated. One may thus ask: What would a CHM, usually delivered between 15 and 20 weeks’ gestation, have looked like at 6 weeks’
Figure 22.7. Hydatidiform mole with degenerating embryo.
There were no vessels in this “malignant” mole. It was the third consecutive CHM and was followed by fatal choriocarcinoma.
The tiny embryo is visible above the 1.0- to 1.5-cm portion of the ruler. The choriocarcinoma of this pregnancy is shown in Chapter 23.
Figure 22.8. Hydropic villi of “early” CHM at 10 weeks’
gestation. Note that only some villi are bulbous and that the connecting mainstem villi are still prominent. (Source:
Benirschke, 1981, with permission.)
gestation? The answer is unknown, but the observations by Sasaki et al. (1967) and Nishimura et al. (1968) sug- gested that typical hydatidiform moles might not be rec- ognized in such young developmental age groups. For that reason these investigators examined a large number of therapeutic abortions in Japan and found no CHMs, although many would have been expected in that popula- tion. Early CHMs might also contain fetal blood vessels, similar to the occasional embryos that have been seen with CHM just enumerated. Blood vessels in the placenta disappear rapidly after fetal death. Their absence from a CHM does not ensure that there never were villous capil- laries. We suggest then that in transitional stages, the dif- ferential diagnosis may be difficult to make by morphology alone. It is here that flow cytometry and DNA fingerprint- ing have become useful adjuncts.
Edmonds (1959) employed the term transitional mole.
Whether it applied to the transition from a more normal young placenta or to what is now known as a partial mole remains unknown. For these reasons, we prefer not to use this terminology. It would be much better if we identified these abortions as diploid androgenetic, triploid, or diploid-triploid moles, if distinctions are needed. The availability of more precise techniques now demands this precision from pathologists. Cohen et al. (1979) suggested that eight of their 4829 elective first-trimester abortion specimens were molar. In our opinion, however, the cri- teria for their diagnosis of CHM and their photomicro- graphs are not convincing.
Microscopically, moles are characterized by swollen villi with apparently empty cisternae. The cisternae result from the dissociation of loose villous connective tissue;
transitional stages are frequently observed (Fig. 22.9).
Characteristically, there are no blood vessels or recogniz- able vascular remnants, with the exception of the cases
alluded to above. An abundance of Hofbauer cells is fre- quent, as it is in PHM. The trophoblastic covering of CHM varies enormously from mole to mole. It may even vary within a mole (Fig. 22.10). Occasionally, the tropho- blast is degenerated or enmeshed in fibrin. Hertig and
Figure 22.9. Microscopic appearance of the villous surface in CHM. The villous core lacks fetal capillaries; it shows marked edema and early cisterna formation at right. There are many Hofbauer cells. The villous surface has normal epithelium at left and markedly hyperplastic trophoblast on the right. H&E¥100.
Figure 22.10. Surface of molar villus with greater degree of trophoblastic proliferation than that seen in Figure 22.9. Note the aneuploidy of many syncytial nuclei and the syncytial cisternae (dilated transport vesicles) at top.
H&E ¥160.
Sheldon (1947) paid particular attention to the nature and abundance of trophoblast. Using this feature, they subdivided moles into groups I to VI (later revised to three groups), from benign to malignant, and sought a correlation with subsequent development of choriocarci- noma and other sequelae. Hertig (1950), however, later stated, “It is well nigh impossible to predict accurately which mole will be followed by this most rapidly malig- nant of all cancers.” Although Douglas (1962) affirmed this relation between graded moles and choriocarcinoma, most other pathologists have had difficulty with so rigor- ously classifying moles, and their results have not allowed a perfect correlation with outcome (Novak, 1950; Hunt et al., 1953; Javey et al., 1979; Genest et al., 1991). A detailed study by Messerli et al. (1987) showed that the classification of moles and related entities had poor cor- relation among different observers. A quantitative study of nuclear dimensions of trophoblastic cells in CHM by Franke et al. (1985) also failed to use such parameters as predictors of outcome. Benign moles are said to have been followed by pulmonary metastases of choriocarci- noma (e.g., Bonnar & Tennent, 1962), and choriocarci- noma has even followed normal pregnancy and abortion.
For these reasons and because clinical follow-up with hCG titers is efficient, this scheme of classifying moles into groups with histologic differences is no longer fol- lowed. A variety of histochemical studies on molar villi have added little useful information regarding pathogen- esis and prognosis (Bur et al., 1962; Lauslahti, 1969).
Several ultrastructural studies of CHM have been undertaken. They also have yielded little additional infor- mation to our understanding of the biology of these pla- cental errors. Wynn and Davies (1964) showed especially clearly the spectrum of cells that are transitional between cytotrophoblast and syncytium. They also pointed to the fluid imbibition by the syncytium, which is often clearly seen light microscopically as empty spaces (vacuolation) in syncytial cytoplasm (Fig. 22.10; see also Fig. 22.26).
They found a correlation between hCG levels and the abundance of syncytium, but not with that of cytotropho- blast. Essentially similar findings were reported by González-Angulo et al. (1966) and Okudaira and Strauss (1967). Merkow et al. (1971), who studied a mole that progressed to choriocarcinoma, were impressed by the lipid inclusions in the syncytiotrophoblast. Ockleford et al. (1989) undertook a scanning electron microscopic study of 31 CHMs and 12 placentas. They observed pecu- liar and novel surface organelles in several moles. These structures are absent from normal trophoblast, especially the reticular organization of the surface that betrays the underlying cytoskeletal architecture of villi.
Several studies have attempted to localize various markers and antigens to molar trophoblast. Thus, to better understand possible immunologic interactions with the mother, HLA antigen characterization of moles has been done. Lawler et al. (1974) found HLA antibodies against hus-
band’s antigens in women with persistent trophoblastic disease, and Berkowitz et al. (1983a) showed that monoclonal anti-HLA antibodies stained villous stroma but not the trophoblast of CHM. Using the per- oxidase antibody technique, Sunderland et al. (1985) showed that class II antigens are not present on molar trophoblast. They detected class I histocompatibility antigens, however, on “proliferating extravil- lous trophoblast and on villous stromal cells, but not on quiescent villous trophoblast.” This finding is similar to those in normal first-trimester pla- centas. When Yamashita et al. (1979) compared the HLA types of parents with those of the molar tissue, they identified the molar antigen as paternal. Berkowitz et al. (1985b) also detected transferrin receptors in the villous trophoblastic surface, similar to those that occur in normal tissue. These investigators localized trophoblast-leukocyte common anti- gens on normal and molar villous surfaces (Berkowitz et al., 1983a, 1986). Rh0(D) antigens were demonstrated on the malignant tropho- blast of a D-negative patient who became sensitized by a choriocarci- noma, which had developed after the delivery of a D-positive child (Fischer et al., 1985). Goto et al. (1980) had previously demonstrated that trophoblast may contain the D antigen, and Tomoda et al. (1981) subsequently suggested that the racial disparity of incidence in gesta- tional neoplastic disease may be secondary to the irregular distribution of the D antigen. Sarkar et al. (1986) found an expression of c-myc and c-ras oncogenes in early trophoblast, CHM, and malignant tropho- blast cell lines. This pattern was absent from an 11-week conceptus.
The expression of merosin, a novel basement membrane protein, was found in normal and malignant trophoblast (Leivo et al., 1989). Remark- ably, this antigen was present only in intermediate trophoblast (X cells:
extravillous trophoblast). It was not in the syncytium or in Langhans’
cells. This observation further suggests that the X cells represent a dis- tinct and separate lineage of chorionic cells. Minami et al. (1993) demonstrated with antibody staining methodology that molar tropho- blast contains inhibin-activin subunits, after having shown earlier their presence in normal placentas. Certain moieties are found in syncytium and cytotrophoblast, others in extravillous trophoblast. But, like the localization of various other placental hormones to different trophoblas- tic components (Sasagawa et al., 1987), the immunologic localization does not necessarily prove that these cells are the production sites.
Trophoblastic production of hormones was further elucidated by studies of moles. Thus, Sagawa et al. (1997) found leptin production in molar pregnancy. Petit et al. (1996) showed an alteration of the elaboration of G proteins in moles and related it to placental lactogen and hCG production. An excessive production of plasminogen activator inhibitor- 1 (PAI-1) was established by Estellés et al. (1996) and related to the increased incidence of PIH in molar gestations. Various other histo- chemical stains were employed by Olvera et al. (2001) without adding really useful new tools to our armamentarium, however.
The prenatal diagnosis of CHM moles is now usually
possible with sonography. Ultrasonography identifies the
lack of a fetus and displays the multiple echogenic signals,
the “speckled” or “snowstorm” appearance of the molar
placental tissue. Additionally, in PHMs a fetus may be
visualized (Harper & MacVicar, 1963). Despite general
knowledge of molar gestations, physicians make the diag-
nosis infrequently at the first antenatal visit (Ringertz,
1970), probably because in early gestation the villous
swelling is only minimal. Other physicians who have
made similar observations have also pointed to the fre-
quent difficulty of early diagnosis (e.g., Stroup, 1956). The
sonographic differentiation from missed abortions was
further refined by the studies of Fine et al. (1989). Gyne-
cologists have had the experience, however, that sonog-
raphy during early pregnancy fails to make the diagnosis
consistently (e.g., Woodward et al., 1980). Romero et al.
(1985), therefore, correlated hCG levels with sonography.
They set the hCG level of 82,350 mIU/mL as a diagnostic criterion, in addition to absent heart movement seen by ultrasonography. The diagnostic accuracy of recognizing moles thereby increased from 41.6% to 88.8%. Amniog- raphy has also been utilized (Gerber, 1970), as has arte- riography (Hendrickse et al., 1964; Borell et al., 1966;
Breit & Schedel, 1970). It is of special interest that ultra- sonographic examination of first trimester pregnancies that eventuated in CHM did not show alterations that could be used to anticipate molar development (Woodward et al., 1980).
OTHER ATTRIBUTES
Maternal hyperthyroidism often accompanies hydatidiform moles (Her- shman & Higgins, 1971; Sanchez & Sanchez, 1998), and sometimes it causes pulmonary edema. Both disappear promptly after evacuation.
The nature of the thyroid-stimulating agent that is presumably released from the placental tissue is controversial. Some findings have suggested that it is identical to placental hCG (Nisula & Taliafouros, 1980). Amir et al. (1984) conducted a detailed study to identify this agent and concluded that it was unlikely to be hCG, but that it must represent another protein moiety released from the trophoblast of moles. Gunas- egaram et al. (1986) suggested that it was a thyroid-stimulating hormone (TSH)-like protein, distinct from the hCG and the luteinizing hormone (LH) that they identified in molar vesicles. Other alterations of enzymes and proteins have been described in molar gestations. Thus a-fetoprotein is consistently absent in choriocarcinoma patients. It is rarely found in moles and then only in low concentration (Ishiguro, 1975). Yoshimatsu et al. (1987) immunologically examined tissues of various types of abortuses for the presence of a-fetoprotein. Molar fluid and trophoblast were consistently negative, but the protein was found in villi of PHM. Elevated serum glutamic oxaloacetic transaminase (SGOT) levels, found in some moles by Tobin (1963), were believed to result from cellular degeneration. Borek et al. (1983) suggested that urinary levels of DNA breakdown products after molar evacuation may be a useful adjunctive measure to indicate successful therapy. They found nucleosides and some DNA-derived enzymes to be elevated when active trophoblast remained after therapy. The disappearance especially of b-aminoisobutyric acid from the urine, even in the presence of persisting hCG levels, forecasts a good prognosis. Lee et al. (1981) found that circulating levels of the pregnancy-specific b1-glycoprotein (SP-1) and placental protein 5 (PP5) were markedly reduced in patients with untreated CHM and choriocarcinoma. They suggested that this measurement was a decisive means for differentiating benign and malignant trophoblast.
The usual means for following patients with CHM is the serial deter- mination of serum hCG levels or its b-subunits. This hormone is concen- trated in molar villi, according to the studies of Sciarra (1970). He found mean values of 1524 mIU/mL in the fluid of small vesicles, and 1202 mIU/mL in the larger villi. Normal values of all hormones and secretory products of neoplastic trophoblast have been ably summa- rized by Clayton et al. (1981). Yedema and colleagues (1993) have constructed a gonadotropin regression curve from 130 patients with no trophoblastic sequelae after the evacuation of a molar pregnancy. They found that 71 of 77 patients with persistent trophoblastic disease could be identified from their elevated hCG levels, and in more than 50% it was possible to achieve this diagnosis within 6 weeks of operation.
Khazaeli et al. (1986) suggested that the determination of a ratio between b-hCG and hCG has prognostic significance. The more malig- nant moles apparently produce significantly more free b-hCG units
(Khazaeli et al., 1989). Ozturk et al. (1988) found that the ratio of b- hCG to hCG fairly reliably distinguishes between normal pregnancy and CHM, and between CHM and choriocarcinoma. Presumably the hCG secretion, known to be of syncytial origin (Yorde et al., 1979;
Bonduelle et al., 1988), reflects the increased quantity of syncytium in moles, rather than a qualitative change in its secretion pattern, although abnormal trophoblast appears to produce an excessive amount of b- hCG subunits. The rate of decline in b-hCG levels following delivery of moles was also summarized by Yuen (1983), a study that also included data on prolactin and estradiol secretion. In general, the b-hCG levels fall rapidly to zero within 8 weeks after evacuation. Bagshawe et al.
(1986) stated that in 42% of women with CHM serum, hCG was undetectable 56 days after evacuation; none of the patients required chemotherapy. Franke et al. (1983b) determined that the average dis- appearance time of serum hCG after CHM was 99.3 days, after PHM 58.9 days, and after hydatid degeneration in abortuses 50.7 days.
They recommended that, provided there is a continued decrease in the levels, therapy not commence before day 100 after evacuation. Human placental lactogen (hPL) levels correlated poorly with hCG levels of moles and choriocarcinomas; they were generally low (Ehnholm et al., 1967). This finding suggests that chorionepithelium is not the principal source of hPL, and that its cellular source, the X cell, has undergone little proliferation during molar development, which is borne out histo- logically. The interpretation of enhanced hCG secretion by moles because of increased villous (and hence trophoblastic) surface may be an oversimplification. The suggestion has been made that it relates to the expression of paternal genes. Goshen and Hochberg (1994), com- menting on a paper by Fejgin et al. (1993) that studied placental hormone secretion, made these interesting comments. They suggested that high hCG values are expected in CHM because of paternal disomy 19 (the hCG locus is on that chromosome); low levels are expected (and found) in triploid PHM with maternal contribution of the extra haploid set.
Numerous studies have examined how the implantation site of moles might differ from that of normal gestation. The reader is referred to the section on X cells (see Chapter 9). In CHMs the site of implanta- tion often shows exuberant trophoblast and, especially, placental site giant cells. They are mostly X cells (extravillous trophoblast), but syncytiotrophoblast is also present. The amount of trophoblast at the placental site may be confusing, and there may be difficulty in differ- entiating it from invasive choriocarcinoma. King (1956) paid special attention to the borderline lesions of gestational trophoblastic neoplasia.
These lesions encompass (1) residual mole and syncytial endometritis, and (2) invasive mole (chorioadenoma destruens). To minimize the problem of recurrent disease, King advocated routine curettage after removal of a CHM.
