14 Histopathologic Approach to Villous Alterations

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14

Histopathologic Approach to Villous Alterations

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How to Assess Villous Histopathology

Evaluation of the placental villous tissue during the routine evaluation of the placenta is important to gain an overall understanding of the normalcy of the placenta and to ascertain possible disorders. If the villous structure is abnormal, this helps to direct one’s attention to certain pregnancy disturbances that may require further study.

In addition, one needs to consider the influences on the villous structure between delivery and preparation of tissue sections, such as the time and mode of cord clamping (Bouw et al., 1976) and the method of fixation (see Chapter 28, Tables 28.8 to 28.10). Different fixatives produce different histologic appearances with which one needs to be familiar. Moreover, the rapidity of fixation is important if such features as edema are to be evaluated properly (Voigt et al., 1978; Kaufmann, 1985).

All these ﬁndings are crucial for a proper microscopic evaluation of villous tissue, which is peculiarly subject to artifacts.

The placental examination can then lead to signiﬁcant insight as to the pathogenesis of many disorders. Salaﬁa et al. (1992), Macara et al. (1996), and Todros et al. (1998) found, for instance, an excellent correlation of various features with intrauterine growth restriction (IUGR).

Importantly, the associated or causative villous pathology was chronic villitis, infarcts, so-called hemorrhagic endovasculitis, thromboses, and fetoplacental vascular maldevelopment. In their quantitative study of placentas from undeﬁned growth-retarded newborns and appropriate controls, Wong and Latour (1966) found only minor changes that would not allow characterization by ordinary microscopy. It was, however, possible only to show that the placentas of growth-retarded neonates had a reduced villous surface area when quantitative measure- ment of villi and trophoblast were made. Since then, however, a much better understanding of IUGR has been gained and one cannot help but believe that the cases studied by these authors had a very mixed etiology. Like-

wise, one must then presume that the placental changes might differ markedly.

Such scrutiny presupposes a considerable familiarity with the normal structure of the placenta and also that sufﬁcient tissue samples have been collected for this study.

For instance, it must be appreciated that the center of placental lobules differs in its villous appearance from that of the lobular periphery. In the central areas and under the chorion the villi are more widely separated, and they may have quite a different appearance from the villi at the periphery of a lobule (see Chapter 7, Fig. 7.18). This organization of the “placentone,” as the German histolo- gists have named this area (Schuhmann, 1981), is particularly well shown in Figure 24 of Becker and Röckelein (1989). Misinterpretation of that feature alone may lead to an assessment of the so-called dysmaturity of villi. Alt- shuler and Herman (1989) characterized villous dysmaturity thus: “Third trimester placentas that have large villi with numerous stromal cells, a lack of syncytiotrophoblast, and syncytiotrophoblastic knots . . . examples are chorangiosis, diabetes, and immunohemolytic anemia.” It must be said, however, that there is no unifying hypothesis to define, let alone explain, “dysmaturity.” We prefer not to use this term at all because it is not sufficiently specific.

Rather, we employ the term villous maldevelopment to mean similar abnormalities in structure when no specific cause is apparent. What is meant is that the villous architecture is admixed; there are perhaps mature villi mixed with edematous or hypercellular immature villi, scarred avascular villi with chorangiosis (Figs. 14.1 to 14.3), and so on. Dysmaturity is not a precise diagnosis and it would be better to describe the abnormality specifically rather than to use the poorly defined term dysmaturity.

Assessment of Villous Maturation

Other considerations concerning errors in villous development have been summarized by Vogel (1996). He suggested that these maturational disturbances occur as

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Figure 14.1. Chorangiosis (grade 2 according to Altshuler, 1984), associated with villitis of unknown origin. H&E ¥90. (Courtesy of Dr. G. Altshuler, Oklahoma City, Oklahoma.)

Figure 14.2. Tenney-Parker changes at 25 weeks’ gestation. This placenta is from a preeclamptic pregnancy and shows features of accelerated maturation. Large numbers of syncytial knots (Tenney- Parker) are everywhere present. H&E ¥64.

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often as in 25% of otherwise normal placentas, albeit only in conﬁned, small areas of the placentone. Most did not have a known fetal impact, although their frequency was

Becker (1981a) Schweikhart (1985) Kloos and Vogel (1974) Vogel (1984)

Normal maturation Synchronous maturation Mature, age-corresponding Mature gestation, age-appropriate

Delayed maturation Discontinuous vascularization Dissociated villous maturation,

mostly mature

Retarded maturation Terminal villi deﬁciency Concordant retarded villi Dissociated villous maturation, mostly immature

Arrested maturation Persisting immaturity Persisting embryonal structure Arrest of villous maturation Premature maturation Asynchronous postterm maturity Premature maturation Villous premature maturation

Chorangiosis Chorangiomatosis Chorangiosis, type I

Pseudochorangiosis Angiomatosis Chorangiosis, type II

Chorangiomatosis Chorangiosis

much increased in problem pregnancies. As there exists no uniform, agreed-upon terminology, Vogel (1996) produced the following table:

Figure 14.3. Marked congestion of villous capillaries and veins in a 30-week placenta of preeclampsia. Note association with increased knotting. Similar congestion of capillaries and veins is usually found after preterm rupture of membranes; it is probably caused by cord compression due to loss of amnionic ﬂuid.

H&E ¥100.

The term placental dysfunction was perhaps first used by Clifford (1954), when he described the features of postmature gestations. He suggested that postmature delivery occurred then as often as in 5% of gestations, and he indicated that perinatal mortality increased sig- nificantly after term. He was emphatic that much of this mortality reflected intrauterine fetal demise and suggested that it resulted from the supposed decrease of placental function. Clifford addressed fetal function but had little to say about placental findings. Meconium dis- charge, deficient water transfer, and meconium aspiration seem to have been the principal aspects of postmaturity he considered, although oxygen deficiency was inferred.

From the pathologist’s point of view there are no truly characteristic histologic ﬁndings that allow one to make the diagnosis of postmaturity in placental examination.

Rather, two different features can be found:

1. In the first group of cases, one finds persisting immaturity with scarcity of terminal villi and prevalence of immature intermediate villi, resembling placentas from the early third trimester (Fox, 1968d; Kemnitz & Theur- ing, 1974; Mikolajczak et al., 1987) (cf. Chapter 8). Other pathologic findings are generally absent. The delay of villous maturation in these cases suggests that postterm delivery was due to absence of placental signals inducing labor. According to Becker (1981a) there was no indication that, from a placental point of view, there was no urgency of delivery.

2. Another quite different entity of postterm placentas shows full villous maturity or even “hypermaturity” with prevalence of mature intermediate and terminal villi and complete absence of immature villous types. The picture may also include increased syncytial knotting (Tenney- Parker changes). Statistically speaking, this type of post-

How to Assess Villous Histopathology 475

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mature placenta is more calcified, but because not all postmature placentas have an excess of calcification, this is a difficult parameter to judge. These placentas are also more frequently meconium stained, and they have more often chorioamnionitis (Naeye, 1992), but not all are so altered (see Chapter 1).

The same heterogeneity of ﬁndings is typical for pre- mature deliveries:

1. The inexperienced pathologist, when studying the histology of a prematurely delivered placenta, expects prevalence of large-caliber, lightly stained immature villous types and scarcity of terminal villi. Surprisingly, this is the case in only 33% of the respective placentas;

the immature villous maturational state corresponds to the premature stage of pregnancy (synchronous villous immaturity) (Schweikhart et al., 1986).

2. The majority of spontaneous preterm deliveries show more advanced villous maturation. Fully mature villous trees or even abnormal-appearing villi showing increased degrees of capillarization occur frequently in prematurely delivered placentas of preeclamptic women.

They are primarily manifest as an increase of syncytial knots (Tenney-Parker changes), smaller villi, and perhaps an increase in the cross sections of capillary lumens (Fig.

14.2). Schweikhart et al. (1986) were impressed with the proliferation of terminal villi in premature placentas, lik- ening their architecture to “bonsai” trees; they found

“hypermature” placentas as often as in 42% of placentas delivered between 29 and 32 weeks. In the case of preeclampsia, the incidence was raised to 60%. This frequent combination of premature delivery with villous maturity has been called accelerated maturation or maturitas praecox placentae (Becker, 1960), to indicate that some villous features indicated greater development than expected for the gestational age. Naeye (1992), however, made the point that this concept of accelerated maturation has often led to confusion and that it is difﬁcult to deﬁne precisely. Becker (1981a) proposed that full maturity of the placenta is needed to be responsible for a spontaneous induction of labor (“placental need for delivery”).

In summary, these data suggest that spontaneous induction of labor requires the coincidence of placental maturation with extraplacental signals. Various mixtures of these two factors allow for ﬁve different combinations, all of which have been described:

1. Normal villous maturation and extraplacental signals at term: term delivery with normal maturity of villi.

2. Normal villous maturation, but delayed or missing extraplacental signals for delivery: postterm delivery with hypermaturity of the placenta.

3. Normal villous maturation, but premature induction of labor: preterm delivery with immaturity of villi (syn- chronous immaturity).

4. Delayed maturation of villi, delayed or missing spon- taneous induction of labor: postterm delivery with immaturity of villi (persisting immaturity).

5. Premature maturation of villi, with preterm induction of labor: preterm delivery with full maturity or even hypermaturity of villi.

Placental Insufﬁciency

The term placental insufficiency is a most difficult one to define precisely. One might expect that placental weight bears on this question, and placental weight has often been used to suggest that the placental function is “ade- quate” or “insufficient.” Ratios to fetal weight have then been used to correlate placental function. Sinclair (1948) found the placental weight to increase linearly as gestation progresses; he was unable to account for the great microscopic variability among placentas. He indicated also that birth weights were lower when a marginal insertion of the umbilical cord was present, a feature that is often neglected in published studies because the cord insertion is usually not recorded. This feature is easiest to observe in dizygotic twin pregnancies, where marked dis- crepancies in size and development can occur.

Garrow and Hawes (1971) examined the proposition of placental weight increases in some detail. They showed that after 42 weeks there was no accumulation of structural proteins in the placenta but that the increasing weight resulted from pooling of fetal blood, a variable that also needs to be carefully controlled for meaningful analysis. After much effort at quantitative analysis they concluded that studies such as the ones reported are “a laborious task, and the yield of additional information is relatively small.” Mayhew and colleagues (1994) assessed placental growth from 12 weeks to term and showed linear growth by “hyperplasia” rather than by ultimate hypertrophy. Generally, the weight ratio given for such comparisons is that of fetus/placenta. Normally, this ratio is between 7 and 7.5, but alterations of the ratio are so frequent that one cannot deduce placental dysfunction from an altered ratio. It is now possible to ascertain sonographically the placental volume (thickness and circum- ference) and to relate it to fetal growth. Perhaps more appropriate correlations will be made in the future with this modality. That these parameters are more useful was impressively shown by early results of studies by Jauniaux et al. (1994).

A consideration of the entity placental insufficiency fits well into the context of this discussion. As can be imag- ined, we prefer not to use this term. It implies a specific placental disease when in fact the malady is usually caused by one of a variety of factors. These include an

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abnormal fetal genome, chronic infection, and a large number of maternal diseases; they may also relate to the localization of the placenta in the uterus. A good case in point to illuminate the semantic complexity is the discussion by Fejgin et al. (1993). These authors suggested that the low gonadotropin secretion of triploid placentas was caused by placental insufﬁciency. A much more cogent and persuasive argument was supplied by Goshen and Hochberg (1994). They explained the secretory levels as being caused by the genetic contribution in the two different types of partial hydatidiform moles (PHMs), and in complete hydatidiform moles (CHMs). Thus, two maternal genomes (in triploidy) leads to low human chorionic gonadotropin (hCG) values, and two paternal genomes (in some cases of PHM, and usually in CHM) leads to excessive secretion of this hormone because of the genetic expression of speciﬁc genes.

For somewhat different reasons, others have also spoken against the use of this all-inclusive term (Gille, 1985; Kuss, 1987), as was quoted in some detail by Vogel (1996). Conversely, Becker and Röckelein (1989) made cogent pleas to retain the term placental insufﬁciency.

They then produced a complex tabular account of the possible causes of placental insufficiency and stated that an insufficient placenta is one of critical reduction of placental exchange membrane. This entity then encom- passes all those features discussed under their special headings, such as preeclamptic changes, chorangiosis, tumors, avascular villi, and excessive fibrin deposits. We prefer to specify and name the lesions rather than to embrace them all in the imprecise terminology of placental insufficiency.

For routine examination of the histologic picture it is important to study various areas in the placenta as they do not all have the same appearance. For example, the peripheral edge of the placenta often has some increased fibrinoid deposition as a normal feature, and some degree of infarction may be present that is not representative of the remainder of the organ. The villi beneath the chorionic plate are also more widely spaced than those of the floor, and this anatomic difference often leads to focal coagulation that is not necessarily pathologic. At the margin of the placenta, infarction and excessive fibrin deposits are common and should be considered to be normal events, if that is the only location of these changes.

Examination of Fetal Stem Vessels

In assessing the adequacy of villous tissue for fetal growth, it is our practice to proceed in an orderly fashion with the examination so that all aspects are inspected and evalu- ated. We begin with the assessment of the umbilical cord and its vessels. It is of interest to know whether the vas- culature is congested, whether there is a sufﬁcient amount

of blood within the vessels, and, importantly, whether there are nucleated red blood cells (NRBCs) within the fetal blood. The presence of NRBCs is abnormal and connotes anemia, previous hypoxia of some duration, or fetal growth disturbances (Bernstein et al., 1997). When NRBCs are found, we make it a practice to check the newborn blood smear to enumerate these cells (see Chapter 8). At this time we also examine the vessels of the umbilical cord for thrombi, inﬂammation, and possible meconium damage.

The vascular system is next studied in the surface of the placenta. Here, the presence or absence of thrombi is carefully assessed. These frequent, important aspects of prenatal pathology are most commonly found in the veins. These surface veins are difﬁcult to differentiate from arteries by histologic study alone. Veins lie usually below the arteries, but it is best to identify them macroscopically. When thrombi are very old, they transform ultimately into “cushions” (see Chapter 12) (de Sa, 1973), organized thickenings of the venous vascular wall. It must be emphasized that some of these cushions are readily misinterpreted as they may represent bifurcations of vessels. The thrombi may be occlusive, and they may also calcify; this change is prominently found in cytomegalovirus (CMV) infections and also when the thrombi are very old. Calciﬁcation also occurs in the walls of vessels when thrombi have been long-standing.

Similar cushions have been described in walls of umbilical arteries, chorionic arteries, and occasionally also in those of larger villous arteries (Emmrich, 1991). Altshuler (1993) stated that he found cushions “associated with clinically diagnosed neonatal asphyxia.” Becker (1981a) intro- duced the term asphyxial inﬁltrates. This view has been contradicted by Emmrich et al. (1998a,b), who did not ﬁnd any correlation between incidence of arterial cushions and signs of hypoxia or acidosis in the neonate.

More often than obliterative thrombosis, one ﬁnds only mural ﬁbrin deposits. These usually betray long-standing diseases and correlate primarily with stasis from cord problems such as knots, entangling, or prolapse. Occa- sionally, mural thrombosis of surface veins results solely from marked twisting of the umbilical cord.

The main stem villous vessels are next inspected. It is in these vessels that hemorrhagic endovasculitis (HEV) is most commonly seen (Sander, 1980), which is primarily a feature associated with stillbirths. It represents in our opinion a postmortem or postthrombotic phenomenon;

the lesion is discussed in greater detail in Chapter 12 (see Thrombosis of the Placental Vascular Tree).

Examination of the Fetal Capillary Bed

The number of capillaries in the terminal villi is next evaluated. They may be markedly congested when the cord has been clamped soon after delivery of the neonate and also

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when maternal diabetes has complicated the pregnancy.

Congestion as shown in Figure 14.3, however, must not be confused with the more ominous condition known as cho- rangiosis (Altshuler, 1984). The designation chorangiosis makes reference to a numerical increase of capillaries within the peripheral placental villi. Although chorangiosis can be a very impressive feature, it does not relate to neoplastic changes such as angiomas, as has been suggested. This condition is presently underrated as an indicator of chronic prenatal hypoxia. In studying the placentas of infants that were admitted to the neonatal intensive care unit of his hospital, Altshuler found that 5.5% had chorangiosis in their placentas. He provided criteria for the evaluation that have not yet been challenged.

What is important about chorangiosis is its relative rarity and that it is strongly correlated with perinatal mortality and a wide variety of pregnancy and placental disorders. It is deﬁnitely a pathologic feature. The appearance is characteristic, and it is obvious that weeks must be required for the degree of capillary proliferation to take place that produces chorangiosis. It is perhaps for these reasons that the lesion had been termed chorangiomatosis in the past (see Chapter 24).

Chorangiosis occurs also in women who have pregnancies at very high altitude (Reshetnikova et al., 1994) and in severely anemic mothers (Kadyrov et al., 1998). That the proliferation of villous capillaries is an adaptation to chronic oxygen deﬁciency is further supported by the experimental results in guinea pigs described by Scheffen et al. (1990). They demonstrated such increase of capillaries when guinea pigs were chronically (45 days) deprived of normal oxygen tension in their environment.

This point is relevant also to the long history of placental studies at high altitude, where the smaller size of infants and placentas found has much interested investigators.

Jackson and her coworkers (1987) have studied the placenta of women at high altitude in Bolivia and compared them with those at sea level. The total villous length was smaller at high altitude, and capillary cross sections were increased. Thus, an altered capillary/villus ratio emerged as being characteristic.

The terminal villi may lack all capillaries, markedly reducing the available exchange area, and its quantity needs to be estimated. Such avascular villi are most common following chronic villitis, as in CMV infection.

Next most commonly, avascular villi result from main stem and surface vessel thrombosis (Fig. 14.4) (Altshuler

& Herman, 1989). In similar degenerative events, McDer- mott and Gillan (1995) have shown that a chronic reduction of fetal blood flow precedes villous infarction. They suggested that siderosis of villous basement membranes, seen so prominently in cases with arterial thrombosis, was a good marker for this reduced flow. Calcifications of villous basement membranes, having a similar appearance, are discussed next.

Villous Architecture and Fibrinoid

Having studied the vasculature, we prefer next to evalu- ate the low-power appearance of the villous architecture.

It is at this time that structural abnormalities are identified that have an only focal distribution. Focal edema (Naeye et al., 1983; Shen-Schwarz et al., 1989; Naeye, 1992; Altshuler, 1993) is easiest to identify at this time and its abundance can then be estimated. Naeye et al. (1983) had described villous edema to occur especially in pla- centas affected by chorioamnionitis but believed it to correlate best with fetal hypoxia. The extent of edema also correlated with low Apgar scores and other features leading to perinatal mortality. Naeye (1992) specifically suggested that severe villous edema may interfere with oxygen delivery to the fetus by compression of capillaries within villi. Edema would also allow one to recognize possibly increased numbers of Hofbauer cells, especially in Rh incompatibility, chronic infections, and maternal diabetes. It is important to note that not all lightly stained villi represent truly edematous villi. Rather normal immature intermediate villi may be misinterpreted as such, as Figure 14.4. Marked fibrosis and “avascularity” of villous dis- trict caused by obliteration of a large surface vessel. Note the extremely thin trophoblastic cover of villi and pyknotic nuclei.

H&E ¥160.

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their reticular stromal core has only a low afﬁnity for conventional histologic stains (see following, and Imma- ture Intermediate Villi in Chapter 7).

During this survey with low-power inspection of the villous tissue, the maturity of villi is adjudicated, perhaps representing the most difficult task in placental examination for the novice. It must be admitted that it is often impossible to accomplish this task accurately, mostly because of preparative problems. Thus, the diagnosis of postmature villi cannot easily be made correctly from villous examination alone. Maternal factors, fixation, and storage all strongly affect the histologic villous appearance and must be weighed. The influence of maternal conditions is perhaps best seen in preeclampsia when the reduced intervillous blood flow leads to the “Tenney- Parker changes” (Tenney & Parker, 1940). These changes are exemplified by a diffuse increase in syncytial knotting and a decreased size of terminal villi caused by lack of interstitial fluid.

An examination of the villous tissue under low power also allows one to identify irregular maturation of villi, foci of fibrosis, and the quantity of fibrin or fibrinoid deposited. A diffuse increase of perivillous fibrin is sometimes interpreted as reflecting chronic intervillous perfu- sional problems (Altshuler, 1993). Alternatively, excessive fibrinoid deposition is a striking feature of the so-called maternal floor infarction syndrome (see Chapter 9). In this condition, not only is the decidual floor heavily infil- trated by “fibrinoid,” but also this material often dissemi- nates throughout the villous tissue and is associated with proliferation of extravillous trophoblast. The villous tissue in such cases is stiff during macroscopic study, is diffusely penetrated with gray fibrin masses (Gitterinfarkt), and may show many microcysts in the increased extravillous trophoblast deposits. Microscopically, the fibrin encases villi that are being strangled, consequently lack vessels, and ultimately die. It strongly correlates with fetal growth retardation and intrauterine fetal demise. Naturally, true infarcts are also noted during this survey and their age is estimated as well (see Infarcts in Chapter 19).

Intervillous Space, Infarcts

Finally, the intervillous space is evaluated. Does it contain thrombi, especially beneath the chorionic plate? Are they fresh or old, and are they the possible sites of fetal bleeding? Are there tumor metastases or other abnormal features that need study with higher magniﬁcation? And are the maternal red blood cells perhaps sickled? Subchori- onic thrombi are common, as was discussed extensively in Chapter 12. Sonographers have often referred to the subchorionic space as being “lucent” and have speculated that sonographic lucencies are meaningful abnormalities of placentation. There is some indication also that lucencies are a possible warning sign of placenta accreta or

placenta percreta. In most, the sonographically identiﬁed subchorionic lucencies disappear with delivery. Never- theless, large laminated thromboses may occur in this location that can interfere with fetal development.

Growth retardation, vascular compromise, and lateral expansion of these thrombi with abruptio have all been described and were discussed in some detail earlier (see Chapter 9). What is not clear from the current literature is the etiology of large “thrombohematomas,” as the larger of these abnormalities have been referred to. Some authors consider them to be related to abruptio placentae, whereas others have likened them to Breus’ mole. We consider it possible that they are accidental expansions of the normal subchorionic thrombi that make up the ﬁbrinous plaques of term placental surface and which arise most likely by eddying and rheologic aberrations in the intervillous circulation. None of these lesions are related to angiomas, even though sonographically they may have similar appearances.

Also evaluation of the width of the intervillous space may give important hints: An unusually wide intervillous space combined with abnormally small villous calibers (see Figs. 14.8 and 15.7) is a usual ﬁnding in postplacental hypoxia (Kingdom & Kaufmann, 1997) (see Types of Hypoxia and Its Effects on Villous Development in Chapter 7). Clinically, this condition is characterized by intrauterine growth restriction combined with absent or reverse end-diastolic umbilical ﬂow (Macara et al., 1996;

Kingdom et al., 1997). In contrast, an extremely narrow, cleft-like intervillous space combined with irregularly shaped, highly branched terminal villi and impressive Tenney-Parker changes (see Fig. 15.5) is characteristic for villi with increased numbers of highly branched capillaries (excessive branching angiogenesis, chorangiosis). It is often found in severe preplacental hypoxia (maternal anemia; Kadyrov et al., 1998) and in uteroplacental hypoxia (IUGR with preserved end-diastolic ﬂow in the umbilical arteries, with or without preeclampsia, Todros et al., 1999).

True placental infarcts result from occlusion of mater- nal vascular supply. They have different qualities sonographically and are also clearly different from thromboses.

They involve actual placental tissue, whereas the thromboses push the villous structures aside. There may be some infarction of villi adjacent to the thromboses, but that is not a major feature. Infarcts are generally the result of disturbances of intervillous circulation, usually secondary to obstruction of maternal arteries in the placental ﬂoor. They also accompany most abruptios. In a true infarct, the trophoblast dies ﬁrst and subsequently the stroma, vessels, and all other components of the villi undergo necrosis. Initially, there is still some nuclear dusting from karyorrhexis, but eventually that disappears too. Early infarcts still possess some fetal red blood cells with hemoglobin and they are therefore red; later the

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hemoglobin lyses and the infarcts turn white or yellowish.

Eventually, infarcts atrophy remarkably and may focally calcify. In the adjacent villous tissue there is frequently some degree of Tenney-Parker change because of the circulatory disturbance and the ensuing local hypoxia.

Virtually all infarcts have the same appearance, and it is uncommon that their microscopic evaluation makes a useful contribution to the understanding of the placental pathology. Although we have recommended that few of them be examined microscopically and, rather, that more noninfarcted tissue be sampled in placentas affected by infarcts, this is not always prudent. Numerous cases of unsuspected choriocarcinoma in situ have now been described in term placentas that have the macroscopic appearance of ordinary infarcts (see Chapter 23). One usually can reliably identify infarcts macroscopically, and then make a judgment as to their volumetric contribution to the whole organ.

Abruptio Placentae

More problematic is the evaluation of abruptio placentae.

When it is very fresh, no histopathology may be visible.

The retroplacental hematoma may have the same appearance as that blood which normally follows placental detachment. Older abruptios tend to compress the villous tissue and are then more easily identiﬁed microscopically.

The blood cells are degenerating, there is laminated ﬁbrin, pigmented macrophages may be present after a few days, and the decidua basalis is degenerated and often replaced by the hematoma. Indeed, this destruction of the decidua basalis usually makes it impossible to identify the maternal blood vessels and the atherosis or thrombosis within them that were responsible for the abruptio.

It is noteworthy that small areas of abruptio placentae are much more common than is usually stated (Benirschke

& Gille, 1977). The reason for this is that most retroplacental hemorrhages do not produce the usually cited clinical symptomatology of sudden abdominal pain and bleeding. Their contribution to fetal well-being may also be much less signiﬁcant than is that of the large retroplacental hemorrhage with detachment of a major portion of placental tissue. Because most abruptios are considered to be the result of trauma or maternal vascular disease, an assessment of the decidual spiral arterioles is desirable. In the locale of the abruption, however, this is usually impossible. The vessels here are often destroyed by the process or have remained behind during the delivery of the placenta. Therefore, one must look in adjacent portions of decidua, and especially in the decidua capsu- laris. Atherosis and thrombosis are often well displayed in these vessels, but it must be cautioned that their absence is not meaningful. These lesions are often very irregularly distributed, and to ascertain their status with certainty requires blunt curettage after delivery of the placenta.

That procedure is not a favorite part of obstetrical care and thus it is not often undertaken. It is therefore frequently impossible to rule out vascular changes as a cause of abruptions, and therefore their etiology remains obscure.

Major Histopathologic Findings

This brief survey lists the major histopathologic observa- tions that should be made in placental microscopy.

Syncytiotrophoblast

The syncytiotrophoblastic cover of the villous trees usually shows considerable variations in thickness, distribution of nuclei, and structure of nuclei. Extremely thin anuclear areas (epithelial plates) and accumulations of nuclei (syncytial knots) are arranged in a mosaic-like pattern. Homogeneous trophoblastic thickness, combined with numerous Langhans’ cells (villous cytotrophoblast), are found in immature placentas (see Fig. 6.13), in persisting villous immaturity, erythroblastosis (see Fig. 15.10), and in most placentas from diabetic mothers (see Fig.

19.6).

Homogeneous trophoblastic thickness, combined with loss of villous cytotrophoblast, is a typical feature of postplacental hypoxia that is discussed in detail in Chapter 15 (see Fig. 15.17) (Fig. 14.5). Extremely thin syncytiotrophoblast with evenly distributed pyknotic nuclei locally forming large knots (Figs. 14.4 and 14.6; also see Fig.

12.60) are additional important features. Most of the latter are indications of accumulation and shedding of apoptotic nuclei (cf. Chapter 6). When they are combined with the absence of villous cytotrophoblast, this usually points to deﬁcient fetal perfusion of the villi (e.g., fetal death, thrombosis of stem vessels). This malperfusion leads to an increased intravillous oxygen partial pressure and failure of villous cytotrophoblast to proliferate and to regenerate the syncytium (see Oxygen and Oxygen- Controlled Growth Factors as Regulators of Villous Development in Chapter 7).

Knotting of the Syncytiotrophoblast

Increased numbers of syncytial knots, sprouts, and bridges are called syncytial knotting, or Tenney-Parker changes.

As discussed in Chapter 15 (see Syncytial Knotting), these features have to be interpreted with care because they are inﬂuenced by the thickness of the section. Küs- termann (1981), Burton (1986a,b), and Cantle et al. (1987) have shown that most of these nuclear accumulations are ﬂat sections of irregularly shaped villous surfaces. An increased incidence of syncytial knotting thus points to abnormal villous shapes (increased branching and bulging

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Figure 14.5. Persisting immaturity near term. Note the slender, straight sections of mature intermediate villi are arranged in parallel and the absence of terminal villi with sinusoidally dilated capillaries. In normal pregnancy, this feature would correspond to the 32nd to 34th week of gestation. It is also a common feature of postmature placentas, combined with IUGR. H&E ¥30.

Figure 14.6. Immature placenta at 30 weeks from a patient with preeclampsia. Note the accelerated maturity (at left) with numerous syncytial knots (Tenney-Parker change) associated with small terminal villi and large immature intermediate villi at right. The latter are not edematous in nature but, rather, display a reticular stroma.

H&E ¥64.

Major Histopathologic Findings 481

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of villi) (see Chapter 15), and they can usually be found under hypoxic conditions. Typical clinical examples include hypertensive disorders (Alvarez et al., 1969) (Fig. 14.6), maternal anemia (Piotrowicz et al., 1969), and pregnancy at high altitude (Jackson et al., 1987). Also, some cases of prolonged pregnancy (see Fig. 15.14) (Essbach & Röse, 1966; Emmrich & Mälzer, 1968) and many cases of preterm delivery (maturitas precox placentae) (Becker, 1981a; Schweikhart et al., 1986) show similar features. When groups of small terminal villi with increased knotting alternate with groups of severely immature villi (Fig. 14.6), preeclampsia is a prominent possibility (see Chapter 19).

The syncytial knots caused by trophoblastic ﬂat sec- tioning just discussed are usually concentrated in groups of terminal villi. Similar trophoblastic features around the surfaces of immature villous types represent, in most cases, villous sprouting. Abnormal degrees of this phe- nomenon can be seen in moles and in several of the chromosomal aberrations (see Chapter 21, Fig. 21.27, and Chapter 22).

Langhans’ Cells

The villous cytotrophoblast is difﬁcult to identify in routine parafﬁn sections. Despite the fact that Langhans’

cells are present at about 20% of the villous surfaces at term, one usually finds only one clearly identifiable Lang- hans’ cell per cross section of any peripheral villus. Lower frequencies of Langhans’ cells (in routine paraffin histol- ogy: fewer than a mean of one visible in two peripheral villous cross sections) are found in postplacental hypoxia (e.g., IUGR with absent end-diastolic flow in the umbilical arteries) (Macara et al., 1996) (see Chapter 15), and in fetally malperfused villi (fetal death, thrombosis of stem vessels) (see Placental Surface Vessels in Chapter 12).

In contrast, increased numbers of Langhans’ cells (in routine parafﬁn histology: more than two visible per peripheral villous cross section) are usual ﬁndings in immature placentas; they also exist in “persisting immaturity” (Becker & Röckelein, 1989) (see Chapter 15), erythroblastosis (Wentworth, 1967; Pilz et al., 1980) (see Chapter 16), maternal anemia (Kosanke et al., 1998) (see Chapter 19), and maternal diabetes mellitus (Werner &

Schneiderhan, 1972) (see Chapter 19). It is said that their number increases with the severity and duration of preeclampsia (Fox, 1997).

Vasculosyncytial Membranes

Vasculosyncytial membranes are the result of sinusoidal dilatation of the terminal villous capillaries, which bulge against the trophoblastic surfaces and attenuate them to thin lamellae (see Figs. 6.4A and 6.7A). The incidence is closely related to fetal villous vascularization. Imma-

ture placentas and cases of “persisting immaturity” (Fig.

14.5; also see Chapter 15) show reduced villous capillar- ization and, consequently, a paucity of vasculosyncytial membranes.

On the other hand, an increased capillarization of terminal villi is found at high altitude (Jackson et al., 1987;

Reshetnikova et al., 1994) and in some other hypoxic disorders (preeclampsia, maternal heart failure, maternal anemia) (Beischer et al., 1970; Alvarez et al., 1970, 1972;

Kadyrov et al., 1998) (see Control of Villous Develop- ment in Chapter 7). It results in an increase of the vascu- losyncytial membranes; it can come about only when these conditions have existed for some time. In IUGR with absent end-diastolic umbilical blood ﬂow, similar features are observed. Here, abnormally long, unbranched capillaries are combined with reduced diameters of terminal villi (Krebs et al., 1996; Macara et al., 1996). Finally, fetal villous congestion (see Fig. 14.1) can increase vasculosyncytial membranes.

Trophoblastic Basement Membrane

In routine parafﬁn sections of normal villi, the trophoblastic basement membrane is usually only seen when special stains are applied, such as aldehyde-fuchsin, peri- odic acid-Schiff (PAS), and immunohistochemistry for collagen IV or laminin. Marked thickening of the base- ment membrane that becomes clearly visible has been described under various pathologic conditions, such as preeclampsia and essential hypertension (Fox, 1968c), maternal diabetes (Liebhart, 1971, 1974), and IUGR with absent end-diastolic umbilical blood ﬂow (Macara et al., 1996). The reason for these basement membrane changes presumably is that constituents of the basal lamina are secretory products of the villous trophoblast; the increased thickness indicates an altered trophoblastic activity, for example, increased secretion or decreased turnover of basal lamina molecules.

Perivillous Fibrinoid

Most perivillous fibrinoid is a blood clotting product. It is found in defects of the villous trophoblastic cover (see Perivillous Fibrinoid in Chapter 6) and here may act as a substitute for damaged trophoblast. The deposition of perivillous fibrinoid is a regular phenomenon, occurring in every placenta, and the amount increases with advancing pregnancy. This increase is particularly true for the stem villi, whose trophoblastic surface is largely replaced by fibrinoid at term (see Figs. 8.11 and 8.12). One normally finds some increase of fibrin encasing larger groups of villi below the chorionic plate (subchorionic laminated fibrin, bosselation), and also in the marginal zone.

Macroscopically visible deposits that embed larger parts of villous trees are abnormal. These are referred to

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as Gitterinfarkts (Becker & Röckelein, 1989), whereas increased amounts of fibrinoid at the base of the placenta belong to the entity known as maternal floor infarction, an important placental disease (see Maternal Floor Infarction in Chapter 9). In obstructing large parts of the maternofetal exchange surface, these deposits may endan- ger fetal growth and survival. Otherwise, disseminated perivillous fibrinoid deposition has no pathologic signifi - cance (Fox, 1967, 1997).

Intravillous Fibrinoid

This different type of fibrinoid has also been referred to as villous fibrinoid necrosis. It must not be confused with the perivillous fibrinoid just discussed. It is a fibrinoid patch that replaces villous stroma and vasculature under- neath a more or less intact trophoblastic cover (see Fig.

3.2F). It occurs occasionally in normal mature placentas, but its incidence is increased in placentas from diabetic mothers and in cases of erythroblastosis fetalis (Fox, 1968a). Its genesis has been discussed in context with immune attacks (Burstein et al., 1973).

Villous Calciﬁcation

Villous calcifications are relatively uncommon and quite different from the minute calcium deposits in fibrinoid that occur with advancing gestation. The latter is found mostly in the floor and septa and was discussed in Chapter 9. Villous calcification may occur when villi have been destroyed by processes of the past such as thrombosis, CMV infection, and infarction (Fig. 14.7). Calcifications of villous tissues are also observed in some retained placental fragments or when the placenta of a fetus papyra- ceus is retained to term. Quantitatively they play no important role in placental pathology.

An entirely different type of calcification is the finely granular deposition of purple-staining calcium precipi- tate in basement membranes of abortuses. It is currently not certain that this represents calcium salts, as other salts have similar staining characteristics. This fine stippling is perhaps the result of deficient transport of materials through the trophoblast but not consumed after fetal death with its cessation of capillary flow. It has no known etiologic role.

Stem Vessels

It was suggested that the number of arteries in peripheral stem villi is decreased in association with umbilical Doppler high resistance (Giles et al., 1985). Since then, the topic of fetal villous arteries has attracted much attention. Studies by other investigators have not cor- roborated this ﬁnding (Jackson et al., 1995; Macara et al., 1995).

The most conspicuous pathologic changes of fetal stem vessels comprise thromboses. These are common features and affect mostly superﬁcial veins. Laminated mural thrombi are our most common ﬁnding. They result primarily from obstruction of venous return to the fetus (cord knots, spirals, and prolapse) and velamentous insertion, and accompany long-standing chorioamnionitis and CMV infection. The main stem vessels and further distal vascular structures may atrophy or disappear completely.

Thrombosis may thus lead to complete atrophy of portions of the villous tissue (see Fig. 12.60). Thrombosis of large arteries is less common, and usually it remains unclear what the etiology might have been. Protein C and S deﬁciencies have been entertained as possible causes but have never been proved. They are extremely serious for fetal development and survival.

Obliterative endarteritis (see Fig. 13.14) and especially hemorrhagic endovasculitis (HEV) (see Fig. 12.62) are prominent aspects of this area. HEV is found nearly exclu- sively in stillborn infants and most often results from postmortem dissolution of the large blood vessels and those of Figure 14.7. Immature placenta with degenerated villi that contain conspicuous areas of calciﬁcation (black, irregular, and fragmented intravillous foci). H&E ¥160.

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stem villi. Identical changes accompany local obliterations (velamentous vessels); there is no convincing evidence that they represent an infection (see Chapter 12).

Other vascular phenomena, such as ﬁbromuscular sclerosis, also occur in stem vessels, primarily arteries.

They are extensively discussed by Fox (1997) and other placentologists. We see them as secondary features of vascular phenomena and usually find them in the “local- ized” form. It is very uncommon to identify such lesions in widespread distribution. They are then related to Doppler flow anomalies and growth restriction (Fok et al., 1990), but a precise etiology has not been identified.

Occlusions of this type are found after infarcts and primarily in long-standing thrombosis. Indeed, when they occur in infarcts we find it unlikely that they are “prolif- erative” in nature; rather, it is more probable that they come about by the condensation of dying tissues. These obliterations are usual findings in placentas associated with fetal demise. We believe them to be secondary features because other diseases nearly always explain the fetal death. In the presence of absent or reversed end- diastolic velocity in Doppler flow studies, and fetal growth retardation, NRBCs are elevated, and Bernstein et al.

(1997) presumed the stem vessel lesions to have derived from thromboses. These were held to be responsible for increased impedance and, thus, growth restriction. By contrast, Krebs et al. (1996) and Macara et al. (1996) studied the vascularization of peripheral villi of growth- restricted neonates and absent end-diastolic flow velocity by scanning and transmission electron microscopy. They found significant villous abnormalities caused by abnormal capillarization, which they declared to be the reason for growth restriction of the fetus. Concentric thickening of media and intima of the tertiary villous vessels were found by Harvey-Wilkes and her colleagues (1996). Asso- ciated with this, they observed elevated endothelin levels and used these findings to explain an increased placental resistance and the fetal growth restriction. But what the original etiology for most of these changes is remains speculative, although thrombosis remains the most attrac- tive hypothesis. For that reason, microembolism studies were undertaken in sheep (Gagnon et al., 1996); the results are similar to the spontaneous occurrence in human placentas.

The extensive discussion of endarteritis obliterans by Fox (1997) includes a photograph (see Fig. 6.23) of a vessel depicting “endothelial swelling.” Others have called similar features endothelial edema. It very likely represents an artifact and has no relationship to endarteritis. Similar discussions occurred in considerations of HIV-related vascular alterations (see Contractility of Umbilical Vessels in Chapter 12). Indeed, the entity has been widely discussed as occurring in diabetes, preeclampsia, erythroblastosis, and other conditions. Rapid ﬁxation and the use of Bouin’s solution usually prevents

“endarteritis” from being recognizable. It must also be said that the peripheral districts of so-called endarteritis are usually not disturbed, negating its importance as a primary disease of the placenta.

Nucleated Red Blood Cells

The fetal blood vessels may contain NRBCs. This is a normal ﬁnding in gestations of less than 3 months’ duration (see Fig. 3.1C). These elements are abnormal in the last trimester, however, especially when they are identi- ﬁed in routine histology. They then betray the fetal response to erythropoietin (EPO), a hormone that is now frequently measured in neonates. When NRBCs are present one must enumerate them in neonatal blood smears as they rapidly decline after birth. They signify fetal anemia, infection, erythroblastosis, transplacental hemorrhage, or, importantly, prenatal hypoxia. Because it takes time for the secretion of these cells from precursor stores (liver, marrow) through the intervention of EPO and perhaps other signals, the presence of NRBCs suggests that fetal tissue hypoxia of whatever type has occurred many hours, perhaps days, before birth. The topic is covered more extensively in Chapter 8 (see Nucleated Red Blood Cells).

Villous Capillarization

The vasculature of villi is difficult to adjudicate because the capillaries tend to collapse after delivery. The degree of collapse depends on the mode of delivery, the mode of cord clamping, the time elapsed between cessation of umbilical circulation and fixation, and the composition of the fixative (see Tables 28.8 to 28.10). Moreover, when the tissue is fixed in inadequate volumes of fixative the tissue becomes compressed. Thus, asymmetrical compression or distortion of the placenta during fixation may cause considerable shifts of intravascular volume with complete collapse in one part of the fetal vascular bed and apparent overdistention in another. Conclusions concerning villous capillarization, therefore, must always take these potential errors into consideration.

Reduced capillarization of the terminal villous tree is found in slightly immature placentas (see Figs. 14.5 and 15.9). This feature is combined with a uniform trophoblastic cover of the mature intermediate villi that show unusually straight and parallel sections because terminal side branches are largely missing (Fig. 14.5; see Chapter 15).

Complete atrophy of capillaries can be found periph- eral to obstructive lesions in the stem vessels (see Placen- tal Surface Vessels in Chapter 12). Small groups of avascular villi are seen in every placenta (Fig. 14.4), but a higher incidence is often combined with IUGR or intrauterine fetal death.

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Hypercapillarization may show different features, some of these have already been considered. Cases of hypoxic hypercapillarization are usually characterized by numer- ous but small capillary cross sections in clusters of aggre- gated terminal villi. The latter are often connected to each other by trophoblastic ﬂat sections. This feature is often referred to as chorangiosis (see Figs. 14.1, 15.6, and 15.16, and Chapter 24) (Bacon et al., 1984; Jackson et al., 1985, 1988). Three-dimensional reconstruction revealed richly branched capillary nets (Scheffen et al., 1990) resulting from branching angiogenesis. Branching angiogenesis is driven by vascular endothelial growth factor (VEGF), the expression of which is upregulated by low oxygen partial pressures (see Chapter 7). Typical examples of hypoxic hypercapillarization are found in maternal anemia (Kadyrov et al., 1998), and in IUGR with preserved end-diastolic umbilical ﬂow with or without preeclampsia (Todros et al., 1999).

One sometimes ﬁnds cases in which very few (usually only two) but locally dilated capillary cross sections occupy extremely small terminal villi (see Fig. 15.13).

These villi have long, unbranched capillary loops (see Figs. 7.17 and 15.6) resulting from excessive nonbranch- ing angiogenesis. The respective terminal villi rarely aggregate, forming clusters of villi connected by syncytial knotting. Rather, they represent a mixture of single villous cross sections measuring only 40 to 60 mm in diameter, together with few ﬁliform longitudinal sections (Fig. 14.8).

These features often exist among premature deliveries (Schweikhart et al., 1986). We observed the most impressive cases of this kind associated with severe IUGR with absent umbilical end-diastolic blood ﬂow (Krebs et al., 1996; Macara et al., 1996; Kingdom et al., 1997) (Fig. 14.8).

This condition is thought to be caused by abnormally high intervillous oxygen partial pressures (postplacental hypoxia) (Kingdom & Kaufmann, 1997).

These features are not always easy to differentiate from villous congestion (see Fig. 14.3), also resulting in overdis- tended peripheral vessels. The presence of overdistended veins in stem villi, the normalcy of villous caliber distribution, the loss of plasma between the erythrocytes, extrava- sations, and signs of hemolysis may be helpful for the diagnosis. Congestion may be the result of cord complica- tions (see the sections Knots and Thrombosis of the Pla- cental Vascular Tree in Chapter 12) and also of thrombosis of major villous stem veins. Finally, we have often observed congestion in cases of premature rupture of the membranes, perhaps because of loss of amnionic ﬂuid thus altering venous umbilical blood ﬂow.

Stromal Architecture and Stromal Fibrosis

Fibrosis of stem villi is a good indicator of placental maturity (see Chapter 8, Figs. 8.2 to 8.12). Fibrosis starts on about the 15th week postmenstruation (p.m.), begins

around the stem vessels, and should be complete a few weeks before term. When reticular, unﬁbrosed connec- tive tissue persists under the trophoblastic membrane, as in Figures 8.5 and 8.6, it signiﬁes immaturity.

Extensive stromal ﬁbrosis is abnormal, especially when it is not restricted to the stem villi (i.e., those with media- endowed vessels). It can be found in “intrauterine growth retardation combined with absent umbilical end-diastolic blood ﬂow” (Macara et al., 1996), in avascular villi following stem vessel obstruction or fetal death (see Fig. 14.4) (Becker, 1981b; Veen et al., 1982), in CMV infection, and in a few other conditions. It has been speculated that increased intravillous oxygen partial pressure stimulates collagen synthesis when it occurs in the maternally well oxygenated but fetally malperfused placenta (for review, see Kaufmann et al., 1993; Kingdom & Kaufmann, 1997).

In contrast, intraplacental hypoxia has been inferred to be responsible for reduced villous ﬁbrosis (Fox, 1968b, Figure 14.8. Placenta at 29 weeks’ gestation associated with severe fetal growth retardation (neonatal death), showing marked accelerated maturation of the terminal villous branches.

The small diameter of terminal villi and the absence of syncytial knotting suggest this is a case of nonbranching angiogenesis in terminal villi caused by postplacental hypoxia (cf. Chapter 15).

As is typical for many cases of accelerated maturation, stem villi remain in their normal immature condition. Their appearance must not be confused with edema. H&E ¥64.

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1997), for example, unﬁbrosed, immature villi in preeclampsia (see Fig. 14.6).

Hofbauer Cells (Macrophages)

These cells can easily be seen within the stromal channels of the immature intermediate villi (see Figs. 7.4 and 7.9).

When one uses immunohistochemical markers for macrophages (CD68 antibodies), it becomes evident that they are present in all villous types throughout all stages of pregnancy, although they may be difﬁcult to see. There- fore, the impression of increased numbers of Hofbauer cells is usually the result of increased numbers of immature intermediate villi. It thus points to an immature placenta or persisting immaturity in a term organ. Other associations are unknown.

An apparent deﬁciency of macrophages is observed in moles and some chromosomal aberrations, especially in their large, pale villi that otherwise have the appearance of immature intermediate villi. In these cases, the pale stroma is very loose and hydropic and does not belong to the reticular type, that which has stromal channels and contains macrophages (see Chapters 21 and 22, Figs. 21.5, 22.9, and 22.21).

Inﬂammatory Changes

Villi may participate in infectious diseases by inﬁltration of mononuclear and polymorphonuclear leukocytes (polys). Polys are rarely within villi; they are most common in the amnionic sac infection syndrome, chorioamnionitis.

When polys are present within villi, this signiﬁes an acute infectious bacterial disease. Acute villitis is a prominent feature of listeriosis, a disease that is disseminated by maternal septicemia. Other maternal bacterial infections, such as staphylococcal sepsis and other bacterial septicemias, are extremely uncommon. They all produce abscesses in the placenta with dissolution of villous tissue.

Much the commonest placental infection recognized is that with cytomegalovirus (CMV). The picture this virus produces is extremely variable. When one ﬁnds plasma cells concentrated in a few villi, especially when they are accompanied by hemosiderin-laden macrophages and villous sclerosis, then CMV infection is likely.

One may then have to search for the typical inclusion bodies, a sometimes difﬁcult task, or stain with immuno- probes or identify the virus with the polymerase chain reaction (PCR) technique. Typical “owl-eye” cells may be found in endothelium, trophoblast, and unidentiﬁed stromal cells (see Fig. 20.48). Other chronic villitides are caused by toxoplasma and syphilis; they are rarely due to rubella and other recognized viruses (see Chapter 20).

Much the most problematic is the entity known as vil- litis of unknown etiology (VUE), which is also discussed at length in Chapter 20. In this villitis chronic inﬂamma-

tory cells predominate but plasma cells and polys are generally absent. The villi, however, may disintegrate as Figure 14.9 shows. Villitis of unknown etiology is frequent and has no known etiology. It may recur in subsequent gestations and, when extensive, it may cause fetal death.

No microorganisms have been discovered as its cause and recent suggestions of the possible inﬁltration with maternal immunocytes are too inconclusive still. They may signal immune recognition of the fetal antigen, but that is far from certain.

Villous Edema or Immaturity

Many authors call every large, pale-staining villus an edematous villus following the description by Naeye et al. (1983). It is our experience that most of these villi are in fact normal immature intermediate villi (Fig. 14.10) (Pilz et al., 1980; Kaufmann et al., 1987). They may cause diagnostic problems, as their reticular stromal core has only a weak afﬁnity for conventional stains because it lacks collagen. The resulting histologic picture is that of a seemingly edematous villus that had accumulated much interstitial ﬂuid.

True edematous villi indeed exist, however, as well.

They are particularly impressive in hydatidiform moles and hydatid degeneration of abortion specimens (Fig.

14.11), but some are found occasionally in infections such as syphilis, toxoplasmosis, CMV infection, and a variety of cases of hydrops (Fig. 14.12). Placentas from erythroblastosis and other causes of hydrops may show a combination of the two features, as most villi display a retarded maturation and many are additionally edematous (Fig. 14.13).

Figure 14.9. Placenta from a patient with villitis of unknown etiology (VUE) at 36 weeks’ gestation. The infant was stillborn.

Note marked inﬁltration of chronic inﬂammatory cells and simultaneous destruction of villous integrity (right). H&E

¥250.

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Figure 14.10. Placenta at 26 weeks’ gestation of a case of con- genital epidermolysis bullosa. The villous architecture, appropriate for this gestational age, is composed of immature intermediate villi with reticular stroma. They are surrounded by small mesenchymal villi. H&E ¥160.

Figure 14.11. Villi of a partial hydatidiform mole caused by triploidy. There is marked villous distention with edema ﬂuid.

On ﬁrst glance, this appearance is similar to that of immature intermediate villi (Figs. 14.10 and 14.13), but the macrophages of normal intermediate villi are lacking. H&E ¥64.

Figure 14.12. Villi of hydropic fetus with Finnish nephrosis. Most villi are severely hydropic, but they are not different from villi in placentas of other hydrops cases. Compare with Figure 14.11. H&E

¥160.

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Small numbers of immature intermediate villi are found in the centers of the villous trees in nearly every mature placenta (see Fig. 7.18). These are the still proliferating villi and may represent a kind of growth reserve. When they occur in disseminated fashion, or even when there is only a prevalence of this villous type, this indicates immaturity, synchronous or asynchronous. It may be found in many cases of preterm delivery (Schweikhart et al., 1986) and of prolonged pregnancy (Fox, 1968d; Kemnitz & Theuring, 1974; Mikolajczak et al., 1987).

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