—  SHORT COURSE #06  —

Placental Development, Indications for and Methods of Examination

Section 4 - Infection

Phyllis C. Huettner, M.D.


Intrauterine infections can have important consequences for the fetus including abortion, stillbirth, active infection in the newborn period and long-term sequelae such as neurologic deficits including cerebral palsy, mental retardation, blindness, deafness and learning disabilities.

There are two broad patterns of placental infection - ascending infections and hematogenous infections, each associated with a characteristic type and pattern of inflammation within the placenta as well as characteristic types of organisms. In general, ascending infections, the most common pattern, are caused by bacteria that pass from the vagina or cervix into the uterus and cause acute inflammation of the fetal membranes (acute chorioamnionitis) and umbilical cord (acute funisitis). In hematogenous infections, a less common pattern, organisms are passed hematogenously from the mother to the placenta and fetus. This pattern is typically due to viral organisms, protozoa (Toxoplasma gondii) and some bacteria (Listeria monocytogenes, Treponema pallidum). The placenta usually shows chronic inflammation of the villi (villitis). Infants may also be infected with bacterial or viral agents after passing through an infected birth canal, a common form of infection with HIV and HSV, but this form of transmission does not involve the placenta.

Ascending Infection and Acute Chorioamnionitis
Chorioamnionitis is the most common form of inflammation in the placenta. It is found in the placentas of about 4% of uncomplicated term deliveries. Chorioamnionitis is strongly correlated with prematurity and is increased in women of low socioeconomic status and African-American women.

It has become clear that infection causes acute chorioamnionitis. The implicated organisms may be aerobic or anaerobic and are typically normal flora or contaminants of the vagina and cervix such as Ureoplasma urealytica, Mycoplasma hominis, bacteroides urealyticus, E. coli, Staphylococci, Streptococci, and Proteus. There is increasing evidence that some of these organisms may ascend from the lower GYN tract weeks or even months before acute chorioamnionitis develops and reside in the uterine tissues including the decidua due to decreased local immunity secondary to pregnancy. Another common organism isolated from amniotic fluid is Fusobacterium nucleatum, the organism seen in case 4.

Case 4: Acute Chorioamnionitis Secondary to Fusobacterium Infection
Microscopically this case is typical of severe necrotizing chorioamnionitis. There is a marked acute inflammatory infiltrate that involves the chorion and the amnion. Extensive karyorrhectic debris is present. The amniotic basement membrane is thickened and eosinophilic. Much of the amniotic epithelium is necrotic or sloughed. Even on the H&E sections you can see numerous long, filamentous organisms involving the amnion. This is an example of fusobacterium chorioamnionitis.

Fusobacterium nucleatum is a gram-negative anaerobe that is ubiquitous in the oral cavity and is associated with periodontal disease. Periodontal disease has recently been recognized as a risk factor for preterm delivery. Fusobacterium nucleatum has been cultured in the amniotic fluid of 10% to 30% of women in preterm labor with intact membranes and in about 10% of women with preterm rupture of membranes. Yet this species of fusobacterium is rarely isolated from the lower genital tract leading investigators to postulate that it is dissemination, probably from oral plaque, that seeds the amniotic cavity. In experimental animals, intravenous injection of Fusobacterium nucleatum colonizes and proliferates in the uterus, beginning in the decidua and spreading to the chorion and amnion, eventually resulting in preterm birth. The pathogenesis in humans is likely similar.

Pathologic Features and Grading of Acute Chorioamnionitis
On gross examination, the fetal membranes in chorioamnionitis are typically normal but in cases of severe or longstanding infection, may be discolored, friable and foul smelling. Sometimes small, white-yellow plaques can be seen on the surface of the umbilical cord when Candida is the etiologic agent.

Both the mother and the fetus (after about 20 weeks) respond to infection in the amniotic cavity. Maternal neutrophils migrate from maternal blood vessels in the decidua, through the decidua, the chorion and eventually into the amnion of the free membranes (membrane roll). Maternal neutrophils also migrate from the intervillous space, which is essentially a maternal blood vessel, and accumulate in the fibrin beneath the chorion, then pass through the connective tissue of the chorion and eventually into the amnion of the fetal plate of the placenta. Fetal neutrophils migrate out of large vessels on the chorionic plate on the side of the vessels closest to the amniotic cavity. In sections of the fetal plate of the placenta, the inflammatory cells will be a mixture of maternal and fetal neutrophils.

Fetal neutrophils may also migrate from the umbilical cord vessels. The umbilical vein is first involved, followed by the artery. Neutrophils are first seen in the clear spaces between smooth muscle cells. Neutrophils may migrate completely through the vessel wall to involve the surrounding Wharton's jelly. If severe, rings or arcs of degenerating neutrophils will surround the umbilical vessels.

Because of the increasingly clear relationship between acute chorioamnionitis and adverse fetal outcome, including long-term sequelae such as cerebral palsy and chronic lung disease, a reproducible grading system has been proposed to facilitate standardization in diagnosis, study and treatment. In this system both the stage (localization) and grade (severity) are determined for the maternal inflammatory response (chorioamnionitis) and the fetal inflammatory response (chorionic vasculitis and funisitis).

Usually bacteria are not seen on histologic sections. When they are, it is important to consider post delivery overgrowth in unfixed specimens, especially those without inflammation. An important exception is group B β-hemolytic streptococci which is such a virulent organism that bacterial colonies may be found even without much inflammation. As we saw in the Case 4, fusobacterium can also be visualized on H&E. Candida is another organisms identified on H&E, usually associated with microabscesses on the surface of the umbilical cord (see below).

The pathogenesis of acute chorioamnionitis is likely different in term and preterm gestations. In term gestations there is a strong relationship between rupture of membranes and the duration of membrane rupture, and the likelihood of developing acute chorioamnionitis. In contrast, in many preterm gestations, it appears that chorioamnionitis precedes and, in fact causes premature membrane rupture and frequently preterm labor. In this situation, low virulence organisms such as Ureaplasma and Mycoplasma ascend into uterine tissues, perhaps very early in pregnancy, and eventually extend from decidua to chorion, amnion and into the amniotic fluid. Uterine contractions can be induced by inflammatory cytokines such as I-1, IL-6 and tumor necrosis factor produced as a result of the inflammatory response. The inflammatory response also releases other factors such as metalloproteases that degrade the extracellular matrix of the membranes and remodel cervical collagen leading to premature cervical ripening and membrane rupture.

Peripheral Funisitis (Candida Infection)
Candida infections have a very characteristic pattern of inflammation in the placenta. The typical finding has been referred to as peripheral funisitis. Grossly, small, yellowish-white plaques, sometimes with a tan or red center, are seen on the surface of the umbilical cord. Microscopically, wedge-shape abscesses are present just beneath the amnion on the outer surface of the umbilical cord. Often the fungal and psuedo-hyphal forms of the organisms can be appreciated on H&E sections but are even more apparent with special stains like PAS or GMS. Occasional cases can show necrotizing funisitis in which there is abundant cellular debris and sometimes calcification in the Wharton's jelly outside the umbilical vessels. Most cases of Candida funisitis also have accompanying acute chorioamnionitis and fungal organisms may be identified in the membranes.

Qureshi et al reported the largest series of Candida funisitis, in which they studied 32 cases over a 14-year period. Seventy-five percent of their cases were premature with a mean gestational age of 31 weeks. Only 16% of infants developed congenital candidiasis, all with skin lesions at birth. Three of the mothers in this series had IUDs in place and two had cerclages, known risk factors for developing intrauterine Candida infection.

Hematogenous Infection
Infectious agents may reach the placenta by hematogenous spread from the mother. Usually organisms that infect the placenta in this way are viruses but this pattern of spread may be seen with some bacterial infections, such as Listeria and syphilis and parasitic infections such as toxoplasmosis. Infections that reach the placenta by the hematogenous route are usually associated with villitis. Villitis is usually not appreciated on gross examination of the placenta. Occasionally, small foci of necrosis may be seen. Sometimes placentas with villitis are enlarged and pale. Microscopically, there is an inflammatory infiltrate in the villi. The inflammatory cells may be lymphocytes, histiocytes, plasma cells and, occasionally, neutrophils or a mixture of these. Rarely, villitis may be composed of granulomatous inflammation. The inflammatory cells may be associated with necrosis of the villous trophoblast and prominent villous agglutination with eosinophilic fibrinoid material or they may infiltrate the villi without destruction. Sometimes the majority of the inflammation is present around the villi (intervillositis). In addition to inflammation, the involved villi may show vascular destruction, stromal hemosiderin and fibrosis. Usually areas of active inflammation, resolving villitis and healed villitis are scattered in a patchy distribution throughout the placenta. Sometimes, however, the villitis is localized to a particular area such as stem villi or basal plate. This distribution does not appear to be related to the etiology.

Studies have shown that examination of four sections of placental parenchyma will detect the vast majority of villitis, although in a more recent study six sections of parenchyma were required to detect 85% of cases. Over 95% of villitis is villitis of unknown etiology (VUE, see below) meaning that an infectious agent will not be identified on histologic sections, electron microscopy or culture. The percentage of cases classified as VUE may change, however, as more advanced molecular techniques to detect infection are applied to these cases. The morphologic features of some of the well known infectious agents can sometimes point to a particular infectious etiology that may be confirmed with immunohistochemistry, PCR, infant and maternal serologies, or detailed clinical history.

Case 5: CMV Villits

Cytomegalovirus
In the United States, CMV is the most commonly identified infectious agent in cases of villitis where an etiology is identified. About 1% of infants are born with congenital CMV infection. About 5% to10% of these will have disseminated disease with hepatosplenomegaly, jaundice, petechiae or death. Ninety percent of congenitally infected infants will have clinically unrecognized disease and about 5% to15% of these will have long-term sequelae such as mental retardation, learning disabilities and sensorineural hearing loss. Congenital CMV infection represents an important public health problem. It is estimated that nearly two billion dollars is spent annually in the U.S. on the care of symptomatic infants with congenital CMV infection. Treatment of congenitally infected infants shortly after birth may decrease the severity of neurologic damage and improve long-term outcome, therefore it is important for pathologists to have a high level of suspicion for CMV and convey positive results immediately to the pediatrician caring for the infant.

Grossly the placenta may be normal, small, if the fetus is growth retarded, or enlarged and pale, if the fetus is anemic. The characteristic microscopic features of CMV villitis are lymphoplasmacytic inflammatory infiltrates, stromal hemosiderin, necrotizing vasculitis, occluded villous vessels and villous necrosis. In about 20% of cases the characteristic eosinophilic intranuclear and basophilic cytoplasmic inclusions can be identified in stromal, endothelial, Hofbauer or trophoblast cells. Immunohistochemistry, in situ hybridization and PCR will detect CMV in the placenta of cases of congenital infection even in cases that are normal histologically or in which the infection is subclinical. In a study of 94 term placentas sent for examination for reasons other than infection, that were normal histologically, 11% had CMV detected by PCR and in situ hybridization. By in situ hybridization, CMV DNA localizes predominantly in the mesenchyme and trophoblast of the villi but is also seen in extravillous trophoblast and decidual cells.

CMV usually infects the fetus in utero. This may occur as a result of a primary maternal infection during pregnancy, the pattern typically seen in women of higher socioeconomic status, or after reactivation of latent viral infection, the pattern typical in women of lower socioeconomic status. Primary maternal infection is more likely to infect the fetus and these fetuses are more likely to be symptomatic. There is evidence that decidual cells or decidual macrophages may serve as a reservoir for CMV and that reactivation from these cells is enhanced as a result of the inflammatory response to concomitant bacterial infections.

Usually infected women are asymptomatic. There are no guidelines for treating CMV that occurs in pregnancy, making the role of screening women for CMV infection unclear. Infection in the neonate may also occur by contact with infected cervical secretions or, rarely, by an ascending route as well as by hematogenous spread..

Herpes Simplex Virus (HSV)
Disseminated HSV infection may cause severe disease and death in the newborn. HSV is usually acquired during delivery through an infected birth canal, but cases of transplacental and/or ascending infection have also been reported. Hematogenous spread is uncommon but is associated with necrotizing lymphocytic villitis or villous necrosis with little inflammation. Fibrinoid necrosis of villous vessels has also been described. Recent work shows that placental factors serve as a barrier to vertical HSV transmission. Syncytiotrophoblast cells show decreased expression of three HSV entry mediators needed for virus to enter cells, effectively preventing access of HSV into the fetal circulation. Ascending infection is associated with acute necrotizing chorioamnionitis, chronic lymphoplasmacytic chorioamnionitis, or acute funisitis. Occasionally, viral inclusions may be seen in the amnion. Immunohistochemistry and in situ hybridization may be helpful in confirming infection.

Varicella-Zoster
Because most women in the U.S. are infected during childhood, Varicella infection during pregnancy is uncommon. About one-fourth of infants born to mothers with Varicella will be clinically infected or show serologic evidence of infection. Only about 1% will develop the most severe manifestations, congenital Varicella syndrome, characterized by cicatricial skin scarring, hypoplastic limbs and ocular defects.

Infection is thought to occur transplacentally yet the majority of placentas are normal. Some cases have been associated with villitis containing lymphocytes, plasma cells, histiocytes, multinucleated giant cells and even poorly formed granulomas. Some have reported nuclear viral-like inclusions in the villi. The decidua may show a lymphoplasmacytic infiltrate.

Parvovirus B19
Parvovirus B19 is a small single-stranded DNA virus that causes erythema infectiousum (Fifth disease), a mild condition characterized by rash and low-grade fever, in children. Healthy adults are usually asymptomatic but may develop polyarthralgia, arthritis or flu-like symptoms. People with sickle cell disease or other chronic anemias may develop aplastic crises following infection.

About 50% of reproductive age women are immune to parvovirus. Of the non-immune women, about 17% will become infected after exposure. Exposure from a household contact, rather than occupational exposure, results in the highest rate of maternal infection. Although most fetuses are unaffected by maternal infection, the risk of fetal death is as high as 9% if infection occurs before 20 weeks gestation. Most affected fetuses are hydropic and die between 20 and 28 weeks gestation. Infection with parvovirus is a very uncommon cause of fetal loss in the first trimester. Whether parvovirus infection may explain a significant number of late second trimester and third trimester non-hydropic losses is controversial.

Parvovirus infects erythrocyte precursors, which have a specific receptor, as well as cardiac myocytes and endothelial cells. Because erythropoesis is markedly increased in the second trimester, destruction of erythroid precursors by parvovirus at this time leads to anemia and hydrops. Direct effects on cardiac myocytes may also contribute. Parvovirus does not cause congenital anomalies.

As with fetal anemia of any cause, the placenta is often large for gestational age and pale. The villi may be edematous and there is marked erythroblastosis. No villitis is seen. The red cell precursors often contain eosinophilic intranuclear glassy inclusions that cause margination of the chromatin. Similar inclusions can be seen in various fetal tissues especially bone marrow, liver and lung. The inclusions are not well visualized in air-dried material (bone marrow smear or other tissue smears). Immunohistochemistry, in situ hybridization and PCR may be useful in confirming the diagnosis. Caution should be exercised in using PCR on placental tissue as this technique may amplify viremic maternal blood and a positive result may not prove fetal infection.

Human Immunodeficiency Virus (HIV)
HIV can be transmitted from infected mother to infant in utero, by transplacental passage, at delivery, or in the postnatal period by breastfeeding. Most cases of vertical transmission occur by contact with maternal blood or secretions during delivery. The role the placenta plays in promoting or preventing transmission of HIV is still not well understood. HIV antigens can be detected by immunohistochemistry and in situ hybridization and HIV DNA by PCR in trophoblast, Hofbauer cells, villous capillary endothelial cells and amnion, but these findings do not correlate well with the results of viral culture or with infant infection.

The pathologic findings in placentas from HIV positive women have not shown a consistent pattern. In one large study, the placentas of HIV positive women showed significantly more chorioamnionitis and plasma cell deciduitis but were less likely than an HIV negative control group to show villitis. In this study about 22% of the infants born to HIV positive women became infected. Interestingly, the placentas of transmitting women in this study were significantly less likely to show chorioamnionitis. Other studies have shown an association between maternal transmission and acute chorioamnionitis and funisitis.

HIV is a tremendous public health problem in large parts of Africa as is malaria. Co-infection with malaria and HIV has important implications for mother and infant. The frequency and severity of malarial infections is increased in pregnant women who are HIV + compared to those that are not. It is thought that this is due to the immunosuppression caused by HIV. These mothers have a significantly greater chance of transmitting HIV to their children. Malaria in the placenta causes significant placental inflammation and tissue destruction which may increase the access of maternal blood to the fetal circulation. The rate of preterm delivery, low birthweight infants and infant mortality are all significantly increased when these infections occur together.

Syphilis
The prevalence of congenital syphilis (CS) had risen dramatically in the 1980's and 1990's to become the second most common cause of chronic intrauterine infection. Rates in the US fell dramatically in the late 1990's but remain quite high in developing nations. The serologic diagnosis of syphilis in the neonate is often problematic. The CDC requires the identification of spirochetes in fetal, neonatal, cord or placental tissues to establish the diagnosis. For this reason, recognition of the placental findings associated with CS is important in targeting cases for special stains and molecular studies.

On gross examination, placentas from cases of CS may be normal or may be enlarged, bulky and edematous. Microscopically, many cases of CS exhibit the classic triad of 1). large, hypercellular, immature villi 2). proliferative fetal vascular changes, characterized by endovascular proliferation with lumen narrowing, perivascular fibroblastic proliferation with loosening and medial hypertrophy and 3). villitis, usually chronic, sometimes acute, plasmacytic or granulomatous. This triad is seen in only 43%, two of three features in an additional 47% and only one of three in 10% of cases of CS. The presence of intra or perivillous neutrophils in combination with proliferative vascular lesions is a particularly good indicator of CS. In addition to the classic triad, some cases of CS are associated with lymphoplasmacytic deciduitis and chorioamnionitis. Necrotizing funisitis, characterized by a band of inflammation and karyorrhectic debris in the cord, is frequently seen in CS but is not specific. How the pathologic findings in the placenta evolve over the course of in utero infection or change with maternal treatment has not been studied.

Adding the pathologic placental features of congenital syphilis, particularly enlarged villi, acute villitis and necrotizing funisitis, to the results of physical examination, long bone X-rays and laboratory tests has been shown to improve the diagnosis of congenital syphilis from 67% to 89% in live-born infants and 91% to 97% in stillborn infants in one study.

There is a strong association between the presence of the classic triad and spirochete organisms on silver stains and Treponema pallidum DNA by PCR. Silver stains may also identify organisms even when the complete triad is not present. In cases of CS the number of organism in the placenta, cord and membranes may be quite low. It is often difficult to identify spirochetes in the villi, but when seen, they are usually present in sclerotic villi adjacent to villitis. Organisms are best seen in the cord, free membranes and decidua and may be identified even when these structures are not inflamed or abnormal. PCR may identify additional cases not identified by staining.

Listeria monocytogenes
The pathologic features of placentas in Listeria monocytogenes infections are different in several respects from those of other villitides. With Listeria infection the predominant inflammatory cell is the neutrophil. These gather between the trophoblast and villous stroma. Palisaded histiocytes and multinucleated giant cells may also be seen. When several inflamed villi coalesce they form small microabscesses. These can sometimes be seen as small white or yellow lesions on gross examination although generally the placenta appears normal grossly. Usually there is also acute chorioamnionitis raising the possibility that the infection may be spread by hematogenous and ascending mechanisms. Sometimes bacteria can be seen in amniotic epithelial cells. The organism is a small rod-shaped or curved gram-positive bacillus. Although difficult to visualize in tissue sections, it may stain with Warthin Starry, Dieterle or Brown-Hopps stains. Recently work with an immunohistochemical stain suggests that this method may be more sensitive than standard special stains.

The consequences of Listeria infection can be quite severe for the fetus and neonate. Listeria may be a cause of spontaneous abortion, prematurity, neonatal sepsis, meningitis, other morbidity and death. Perinatal infections are of two types - early onset and late onset. Early onset infections typically occur within a few hours of delivery and are associated with septicemia (85%) and respiratory disease (38%). This form has a high mortality rate (30 to 63%) and is usually associated with a history of maternal disease and isolation of Listeria monocytogenes from maternal sites. Late onset disease occurs five or more days after delivery and is associated with septicemia and meningitis but has a lower mortality rate (0 to 25%). Typically this pattern is not associated with a history of maternal illness and Listeria monocytogenes is not cultured from maternal sites.

Mothers become infected after ingesting food contaminated with Listeria, often an unpasteurized dairy product or unwashed vegetables. Most cases are sporadic but epidemics do occur. Adults are usually not acutely ill but pregnant women develop a febrile, flu-like illness and have a 20-fold increased incidence compared to other adults. The increased severity of disease in pregnant women and the propensity to infect the fetus appears to be related to decreased T cells and macrophages and ineffective macrophage function due to properties of the endometrial stromal cells during pregnancy.

Toxoplasma Gondii
The placental findings in Toxoplasma gondii infections are highly variable. On gross examination, the placenta may be normal or enlarged and edematous. Microscopically, villitis is usually seen but it may be subtle and non-necrotizing or extensively necrotizing with fibrosis. Usually the inflammatory infiltrates are composed of lymphocytes and histiocytes; plasma cells are not typically present. Sometimes true granulomas with central necrosis and palisaded histiocytes are present in the inflamed villi. In addition to villitis, other findings include decidual plasma cells, increased nucleated red cells in fetal vessels, a hemorrhagic endovasculitis-like picture, chronic chorioamnionitis and funisitis, and thrombosis and calcification of large chorionic vessels on the fetal plate.

Usually the encysted organism is the form that is identified in placental tissues. It may be found in the cord, membranes, decidua or villi and may be difficult to identify, as the cysts are usually not associated with inflammation. Tachyzoites released from the cysts are associated with marked inflammation and necrosis. Immunohistochemistry, immunofluorescence and PCR may all aid in making the diagnosis.

Congenital toxoplasmosis almost always occurs after primary maternal infection in pregnancy; rare cases of infection after reactivation have been reported. In the U.S. only a third of adult women are immune, therefore the majority of pregnant women are at risk for primary infection. This occurs from ingesting oocyts from cat feces, soil or unwashed vegetables or tissue cysts from undercooked meat. Transmission to the fetus occurs in 35 to 50% of primary maternal infections. The risk of transmission increases the later in gestation the mother acquires the infection but the severity of sequelae in the infant is increased if infection is acquired earlier in gestation. The majority of congenitally infected infants are asymptomatic at birth but most will develop sequelae such as blindness, deafness, microcephaly and decreased IQ. Because treatment during pregnancy as close to infection as possible significantly reduces the number of infants with sequelae and the number with severe sequelae, there has been intense interest in optimizing screening programs in areas with high rates of infection.

Villitis of Unknown Etiology (VUE)
The vast majority of cases of villitis represent villitis of unknown etiology (VUE) in which an infectious etiology cannot be established. The incidence of VUE varies with the population studied and ranges from 6% in a U.S. series to 26% in Argentina.

The placentas from most cases of VUE are normal on gross examination. Microscopically, about 85% are very mild or mild in extent meaning that six or fewer foci are identified in four sections of placenta. In most cases the villitis is randomly distributed throughout the placenta but about 20% have an exclusive or partial basal/parabasal distribution, often with associated decidual inflammation. Most cases are necrotizing and are composed of lymphocytes and histiocytes. There may be associated vasculitis of fetal stem vessels with associated downstream avascular terminal villi.

There are two schools of thought about the pathogenesis of VUE. One proposes that VUE is the result of an as yet unidentified infectious pathogen. A diligent search for pathogens has been ongoing for several decades now and no consistent patterns of infection have been detected in cases of VUE. Recent studies, however, have examined selected patients with unexplained mortality or severe morbidity such as unexplained acute systemic illness, respiratory death or neurologic compromise at birth, for infectious agents. In situ hybridization was utilized to search for DNA viruses and RT-PCR utilizing a bacterial concensus primer was used to search for bacterial organisms. In about 75% of these cases, using these methods, an infectious etiology was found. The most common was Coxsackie virus. Villitis was seen in only a minority of these cases however. Perhaps studies such as these, which utilize molecular techniques to look for a wide variety of infectious agents, in cases of villitis of unknown etiology would also find evidence of an infectious etiology.

Another theory proposes that VUE is an immunologic phenomenon. This seems more likely. The cells in foci of villitis have been demonstrated to be primarily maternal in origin and to represent T helper cells and Ia antigen-bearing macrophages as would be expected in an allograft reaction, in this case host versus graft, between maternal and fetal tissues. This theory is also in keeping with clinical features such as an increased incidence of maternal autoimmunity in women with placental VUE and the tendency for VUE to recur in some patients in subsequent pregnancies. The target antigen of maternal attack is still not known.

Although in most cases of VUE the fetus is unaffected, it has been significantly associated with small for gestational age infants and antenatal growth arrest, perinatal mortality, oligohydramnios not related to membrane rupture and to chronic monitoring abnormalities. These more severe clinical complications are usually associated with more severe villitis. VUE is most commonly seen in placentas from gestations over 32 weeks of age.

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Chronic chorioamnionitis
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  2. Jacques S and Qureshi F. Chronic chorioamnionitis: a clinicopathologic and immunohistochemical study. Hum Pathol,.1998; 29(12):1457-61.
Candida
  1. Qureshi F, Jacques S, Bendon R, et al. Candida funisitis: A clinicopathologic study of 32 cases. Pediatr Dev Pathol. 1998; 1:118- 24.
Cytomegalovirus
  1. Fisher S, Genbacev O, Maidji E, et al. Human cytomegalovirus infection of placental cytotrophoblasts in vitro and in utero: implications for transmission and pathogenesis. J Virol. 2000; 74(15):6808-20.

  2. Guerra B, Lazzarotto T, Quarta S, et al. Prenatal diagnosis of symptomatic congenital cytomegalovirus infection. Am J Obstet Gynecol 2000; 183(2):476-82.

  3. Halwachs-Baumann G, Genser B, Danda M, et al. Screening and diagnosis of congenital cytomegalovirus infection: a 5-year study. Scand J Infect Dis 2000; 32(2):137-42.

  4. Kumazaki K et al. Detection of cytomegalovirus DNA in human placenta. J Med Virol 2002; 68:363-9.

  5. Modlin JF et al. Case 25-2003: A newborn boy with petechiae and thrombocytopenia. NEJM 2003; 349:691-700.

  6. Mostoufi-zadeh M, Driscoll S, Biano S, et al. Placental evidence of cytomegalovirus infection of the fetus and neonate. Arch Pathol Lab Med. 1984; 108(5):403-6.

  7. Muhlemann K, Miller R, Metlay L, et al. Cytomegalovirus infection of the human placenta: an immunocytochemical study. Hum Pathol. 1992; 23(11):1234-7.

  8. Nakamura Y, Sakuma S, Ohta Y, et al. Detection of the human cytomegalovirus gene in placental chronic villitis by polymerase chain reaction. Hum Pathol. 1994; 25(8):815-8.

  9. Pereira L et al. Human cytomegalovirus transmission from the uterus to the placenta correlates with the presence of pathogenic bacteria and maternal immunity. J Virol 2003; 77:13301-13314.

  10. Sachdev R, Nuovo G, Kaplan C, et al. In situ hybridization analysis for cytomegalovirus in chronic villitis. Pediatr Pathol 1990; 10(6):909-17.

  11. Stagno S, Pass R, Dworsky M, et al. Congenital cytomegalovirus infection: the relative importance of primary and recurrent maternal infection. N Engl J Med. 1982; 306(16):945-9.

  12. Stagno S and Whitley R Herpesvirus infections of pregnancy. Part I: Cytomegalovirus and Epstein-Barr virus infections. N Engl J Med 1985; 313(20):1270-4.

  13. Trincado DE et al. Highly sensitive detection and localization of maternally acquired human cytomegalovirus in placental tissue by in situ polymerase chain reaction. J Infect Dis 2005;192;650-7.

  14. Whitley RJ, Cloud G, Gruber W et al. Ganciclovir treatment of symptomatic congenital cytomegalovirus infection: results of a phase II study. J Infect Dis. 1997; 175:1080-6.
Herpes Simplex Virus (HSV)
  1. Altshuler G. Pathogenesis of congenital herpesvirus infection. Case report including a description of the placenta. Am J Dis Child.1974; 127(3):427-9.

  2. Koi H et al . Syncytiotrophoblast is a barrier to maternal-fetal transmission of herpes simplex virus. Biol Repro 2002; 67:1572-79.

  3. Schwartz D and Caldwell E. Herpes simplex virus infection of the placenta: the role of molecular pathology in the diagnosis of viral infection of placental-associated tissues. Arch Pathol Lab Med 1991; 115(11):1141-4.

  4. Sickel J and di Sant'Agnese A. Anomalous immunostaining of "optically clear" nuclei in gestational endometrium: a potential pitfall in the diagnosis of pregnancy-related herpes virus infection. Arch Pathol Lab Med . 1994; 118:831-3.

  5. Witzleben CM and Driscoll SG. Possible transplacental transmission of herpes simplex infection. Pediatrics. 1965; 35(2):192-199.
Varicella-Zoster
  1. Qureshi F and Jacques S. Maternal varicella during pregnancy: correlation of maternal history and fetal outcome with placental histopathology. Hum Pathol. 1996; 27(2):191-5.

  2. Robertson N and McKeever P. Fetal and placental pathology in two cases of maternal varicella infection. Pediatr Pathol. 1992; 12(4):545-50.
Parvovirus
  1. Anand A, Gray E, Brown T, et al. Human parvovirus infection in pregnancy and hydrops fetalis. N Engl J Med. 1987; 316(4):183-6.

  2. Berry P, Gray E, Porter H, et al., Parvovirus infection of the human fetus and newborn. Semin Diagn Pathol. 1992; 9(1):4-12.

  3. Caul E, Usher J, and Burton P. Intrauterine infection with human parvovirus B19: a light and electron microscopy study. J Med Virol. 1988; 24(1):55-66.

  4. Harger J, Adler S, Koch W, et al. Prospective evaluation of 618 pregnant women exposed to parvovirus B19: risks and symptoms. Obstet Gynecol 1998; 91(3):413-20.

  5. Krause J, Penchansky L, and Knisely A. Morphological diagnosis of parvovirus B19 infection: a cytopathic effect easily recognized in air-dried, formalin-fixed bone marrow smears stained with hematoxylin-eosin or Wright-Giemsa. Arch Pathol Lab Med. 1992; 116(2):178-80.

  6. de Krijger R, van Elsaker-Niele A, Mulder-Stapel A, et al. Detection of parvovirus B19 infection in first and second trimester fetal loss. Pediatr Pathol Lab Med. 1998; 18(1):23-34.

  7. Nyman M et al. Detection of human parvovirus B19 infection in first-trimester fetal loss. Obstet Gynecol 2002; 99:795-8.

  8. Tolfvenstam T, Papadogiannakis N, Norbeck O, et al. Frequency of human parvovirus B19 infection in intrauterine fetal death. Lancet. 2001; 357(9267):1494-7.

  9. Vogel H, Kornman M, Ledet S, et al., Congenital parvovirus infection. Pediatr Pathol Lab Med. 1997; 17(6):903-12.
Human Immunodeficiency Virus (HIV)
  1. Brahmblhatt H et al. The effects of placental malaria on mother-to-child HIV transmission in Rahai, Uganda. AIDS 2003;17:2539-41.

  2. Burgess T. Determinants of transmission of HIV from mother to child. Clin Obstet Gynecol. 2001; 44(2):198-209.

  3. Chandwani S, Greco A, Mittal K, et al. Pathology and human immunodeficiency virus expression in placentas of seropositive women. J Infect Dis. 1991; 163(5):1134-8.

  4. Fowler M. Update: transmission of HIV-1 from mother to child. Curr Opin Obstet Gynecol. 1997. 9(6):343-8.

  5. Jauniaux E, Nessmann C, Imbert M, et al. Morphological aspects of the placenta in HIV pregnancies. Placenta 1988; 9(6):633-42.

  6. Lewis S, Reynolds-Kohler C, Fox H, et al. HIV-1 in trophoblastic and villous Hofbauer cells, and haematological precursors in eight-week fetuses. Lancet. 1990; 335(8689):565-8.

  7. Martin A, Brady K, Smith S, et al. Immunohistochemical localization of human immunodeficiency virus p24 antigen in placental tissue. Hum Pathol. 1992; 23(4):411-4.

  8. Mattern C, Murray K, Jensen A, et al. Localization of human immunodeficiency virus core antigen in term human placentas. Pediatrics. 1992; 89(2):207-9.

  9. Mwamyumba F et al. Placental inflammation and perinatal transmission of HIV-1. JAIDS. 2002; 29:262-69.

  10. Schwartz DA et al. Placental abnormalities associated with human immunodeficiency virus type 1 infection and perinatal transmission in Bangkok, Thailand. J Infect Dis. 2000; 182:1652-7.
Syphilis
  1. Berry M, and Dajani A. Resurgence of congenital syphilis. Infect Dis Clin North Am. 1992; 6(1):19-29.

  2. Genest D, Choi-Hong S, Tate J, et al. Diagnosis of congenital syphilis from placental examination: comparison of histopathology, Steiner stain, and polymerase chain reaction for Treponema pallidum DNA. Hum Pathol. 1996; 27(4):366-72.

  3. Qureshi F, Jacques S, and Reyes M. Placental histopathology in syphilis. Hum Pathol. 1993; 24(7): 779-84.

  4. Russell P and Altshuler G. Placental abnormalities of congenital syphilis: a neglected aid to diagnosis. Am J Dis Child. 1974; 128(2):160-3.

  5. Schwartz D, Larsen S, Beck-Sague C, et al. Pathology of the umbilical cord in congenital syphilis: analysis of 25 specimens using histochemistry and immunofluorescent antibody to Treponema pallidum. Hum Pathol. 1995; 26(7):784-91.

  6. Sheffield JS et al Placental histopathology of congenital syphilis. Obstet Gynecol 2002; 100:126-33.

  7. Walter P, Blot P, and Ivanoff B. The placental lesions in congenital syphilis: a study of six cases. Virchows Arch A Pathol Anat Histol 1982; 397(3):313-26.
Listeria
  1. Benshushan A et al. Listeria infection during pregnancy: a 10 year experience. IMAJ 2002; 4:776-780.

  2. Driscoll S, Gorbach A, and Feldman D. Congenital listeriosis: diagnosis from placental studies. Obstetrics and Gynecology. 1962; 20(2):216-20.

  3. Klatt E, Pavlova Z, Terberg G, et al. Epidemic perinatal listeriosis at autopsy. Hum Pathol. 1986; 17:1278-81.

  4. Parkash V, Morotti R, Joshi V, et al. Immunohistochemical detection of listeria antigens in the placenta in perinatal listeriosis. Int J Gynec Pathol. 1998; 17:343-50.

  5. Redline R and Lu C, Role of local immunosuppression in murine fetoplacental listeriosis. J Clin Invest 1987; 79:1234-41.

  6. Redline R, Shea C, Papaioannou V, et. Al. Defective anti-listerial responses in deciduoma of pseudopregnant mice. Am J Pathol 1988; 133(3):485-96.

  7. Scully R, Mark E, McNeely W, et al. Weekly clinicopathological exercises. N Eng J Med 1997; 336(20):1439-46.

  8. Silver H. Listeriosis during pregnancy. Obstet Gynecol Surv. 1998; 53(12):737-40.

  9. Yamazaki K, Price J, and Altshuler G. A placental view of the diagnosis and pathogenesis of congenital listeriosis. Am J Obstet Gynecol 1977; 129(6):7035.
Toxoplasma Gondii
  1. Altshuler G. Toxoplasmosis as a cause of hydranencephaly. Am J Dis Child. 1973; 125(2):251-2.

  2. Chabbert E et al. Comparison of two widely used PCR primer systems for detection of Toxoplasma in amniotic fluid, blood and tissues. J Clin Micro 2004; 42:1719-22.

  3. Desmonts G and Couvreur J. Congenital toxoplasmosis: a prospective study of 378 pregnancies. N Engl J Med, 1974. 290(20):1110-6.

  4. Elliott W. Placental toxoplasmosis: report of a case. Am J Clin Pathol. 1970; 53(3):413-7.

  5. Foulon W, Villena I, Stray-Pederse B, et al. Treatment of toxoplasmosis during pregnancy: a multicenter study of impact on fetal transmission and children's sequelae at age 1 year. Am J Obstet Gynecol 1999; 180(2 Pt 1):410-5.

  6. Fricker-Hidalgo H, Pelloux H, Racinet C, et al. Detection of Toxoplasma gondii in 94 placentae from infected women by polymerase chain reaction, in vivo, and in vitro cultures. Placenta 1998; 19(7):545-9.

  7. Kravetz JD and Federman DG. Toxoplasmosis in pregnancy. Am J Med 2005;118:212-16.

  8. Popek E. Granulomatous villitis due to Toxoplasma gondii. Pediatr Pathol. 1992; 12(6): p. 281-288.

  9. Tsai M and O'Leary T. Identification of Toxoplasma gondii in formalin-fixed, paraffin-embedded tissue by polymerase chain reaction. Mod Pathol 1993; 6(2):185-8.
Villitis of Unknown Etiology
  1. Altemani A. Immunohistochemical study of the inflammatory infiltrate in villitis of unknown etiology. Path Res Pract. 1992; 188:303-9.

  2. Altshuler G, Russell P, and Ermocilla R. The placental pathology of small-for-gestational age infants. Am J Obstet Gynecol. 1975; 121(3):351-9.

  3. Becroft DM et al. Placental villitis of unknown origin: epidemiologic associations. Am J Obstet Gyn 2005;192:264-71.

  4. Genen L et al. Correlation of in situ detection of infectious agents in the placenta with neonatal outcome. J Pediat 2004; 144:316-20.

  5. Jacques S and Qureshi F. Chronic intervillositis of the placenta. Arch Pathol Lab Med. 1993; 117:1032-5.

  6. Knox W and Fox H. Villitis of unknown aetiology: its incidence and significance in placentae from a British population. Placenta. 1984; 5:395-402.

  7. Labarrere C, Althabe O, and Telenta M. Chronic villitis of unknown aetiology in placentae of idiopathic small for gestational age infants. Placenta. 1982; 3:309-17.

  8. Labarrer C, McIntyre, J and Faulk P. Immunohistologic evidence that villitis in human normal term placentas in an immunologic lesion. Am J Obstet Gynecol. 1990; 162(2):515-22.

  9. Redline R and Abramowsky C. Clinical and pathologic aspects of recurrent placental villitis. Hum Pathol. 1985; 16(7):727-31.

  10. Redline R and Patterson P. Villitis of unknown etiology is associated with major infiltration of fetal tissue by maternal inflammatory cells. Am J Pathol. 1993; 143(2):437-9.

  11. Redline R and Patterson P. Patterns of placental injury. Arch Pathol Lab Med. 1994; 118:698-701.

  12. Russell P. Inflammatory lesions of the human placenta. III: The histopathology of villitis of unknown aetiology. Placenta 1980; 1:227-44.

  13. Satosar A et al. Histologic correlates of viral and bacterial infection of the placenta associated with severe morbidity and mortality in the newborn. Hum Pathol 2004; 35:536-45.