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Placenta

Infectious conditions

Chorioamnionitis

Reviewers: Mandolin Ziadie, M.D. (see Reviewers page)
Revised: 26 January 2013, last major update September 2011
Copyright: (c) 2003-2013, PathologyOutlines.com, Inc.

Definition
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● Maternal inflammatory response usually due to ascending bacterial infection by group B streptococci, Listeria monocytogenes and fusobacterium (fusobacterium caused 18% of cases, detect with Warthin-Starry stain, Arch Pathol Lab Med 1985;109:739)
● Two or more microbes are common
● May cause premature rupture of membranes
● Major cause of fetal/neonatal infection, stillbirth, prematurity and perinatal morbidity and mortality

Clinical features and Diagnosis
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● Maternal temperature > 37.8 C plus two of the following: maternal or fetal tachycardia, uterine tenderness, foul amniotic fluid odor or leukocytosis
● Clinical features have poor specificity and sensitivity for prediction of histologic chorioamnionitis
● Associated with premature rupture of membranes
● Associated with occult congenital syphilis in stillborn (Arch Pathol Lab Med 1994;118:44)
● More frequent and severe with younger gestational age
● Note: fetal hypoxia and meconium staining of membranes do NOT cause inflammatory changes in placenta

Gross description
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● Dull, opaque membranes with yellow-green discoloration and cloudy amniotic fluid, possibly with purulent exudate
● May be grossly normal

Micro description
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● Neutrophilic infiltrate of free membranes and those overlying the chorionic plate
● Variable fetal response including funisitis and chorionic plate vasculitis
● May have acute intervillositis (often due to Listeria monocytogenes) or peripheral funisitis (often due to Candida)

Grading
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Stage 1 (mild): Acute subchorionitis / acute chorionitis:
● Neutrophils in subchorionic fibrin or interface between deciduas and chorion

Stage 2 (moderate): Acute chorioamnionitis:
● Neutrophils in connective tissue plane between chorion and amnion

Stage 3 (severe): Necrotizing chorioamnionitis:
● Necrosis, amnion sloughing, thickening of amnion basement membrane and neutrophilic karyorrhexis
● Multifocal abcesses may be present

Micro images
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Acute inflammation


Acute exudative inflammation present with microabscess formation in decidua


Figure 1B

Subacute chorioamnionitis
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● May indicate long standing infection by pathogens of low virulence
● Prolonged (subacute) inflammation with amniotic necrosis is associated with chronic lung disease (bronchopulmonary dysplasia, Wilson-Mikity syndrome, Hum Pathol 2002;33:183)
● Mixed cell infiltrate of mononuclear cells and neutrophils, primarily in the amnion and upper chorion

Chronic chorioamnionitis
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● Rare; etiology unknown
● Primarily lymphocytic infiltration of chorioamnion, associated with chronic villitis of unknown etilogy (71%), maternal hypertension (20%), preterm infants (40%) and intrauterine growth restriction (15%) (Hum Pathol 1998;29:1457)

End of Placenta > Infectious conditions > Chorioamnionitis

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