Definition/General
Introduction:
Acute villitis is characterized by neutrophilic infiltration of chorionic villi
It represents acute inflammatory response (<1 week duration)
It typically results from bacterial infections via hematogenous spread
It may be part of ascending infection pattern.
Origin:
Results from hematogenous bacterial spread to placenta
Ascending infection from lower genital tract
Direct inoculation during procedures
Maternal bacteremia
Spread from adjacent infected tissues
Listeria monocytogenes is classic cause.
Classification:
Classified by causative organism
By severity: Mild, moderate, severe
By distribution: Focal vs diffuse
Stage-based: Early (neutrophil infiltration) vs late (microabscess formation).
Epidemiology:
Less common than chronic villitis
Incidence approximately 1-3% of pregnancies
More common with maternal immunocompromise
Associated with preterm delivery
Higher incidence in developing countries.
Clinical Features
Presentation:
Maternal fever and systemic illness
Preterm labor
Fetal distress
Stillbirth (severe cases)
Purulent amniotic fluid
Maternal leukocytosis
Signs of sepsis.
Symptoms:
Fever, chills, malaise
Abdominal pain and uterine tenderness
Purulent vaginal discharge
Nausea and vomiting
Tachycardia
Signs of dehydration
Altered mental status (severe sepsis).
Risk Factors:
Immunocompromised state
Poor prenatal care
Invasive procedures
Prolonged rupture of membranes
Chorioamnionitis
Bacterial vaginosis
Listeria exposure (unpasteurized dairy).
Screening:
Complete blood count with differential
Blood cultures
C-reactive protein
Procalcitonin levels
Amniotic fluid analysis
Fetal heart rate monitoring
Maternal vital signs monitoring.
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Gross Description
Appearance:
Placenta may show areas of hemorrhage and necrosis
Purulent exudate on surfaces
Friable tissue with easy bleeding
Yellow-white areas of inflammation
Foul odor may be present.
Characteristics:
Hemorrhagic and edematous placental tissue
Areas of softening and friability
Purulent material on maternal and fetal surfaces
Increased placental weight (edema)
Congested blood vessels.
Size Location:
May involve entire placenta (diffuse pattern) or focal areas
Random distribution
Can affect any cotyledon
Maternal surface often more severely affected
Chorionic plate involvement variable.
Multifocality:
Often shows diffuse involvement
May have multiple foci of severe inflammation
Confluent areas of necrosis
Skip lesions less common than in chronic villitis.
Microscopic Description
Histological Features:
Dense neutrophilic infiltrate in villous stroma
Microabscess formation
Villous edema and congestion
Endothelial swelling
Syncytiotrophoblast necrosis
Bacterial colonies may be visible.
Cellular Characteristics:
Predominant neutrophilic infiltration
Degenerative neutrophils with karyorrhexis
Endothelial cell swelling and damage
Extravasated red blood cells
Villous stromal edema
Bacterial organisms within tissues.
Architectural Patterns:
Loss of villous architecture
Villous swelling and distortion
Microabscess formation
Vascular congestion and thrombosis
Fibrin deposition
Intervillous space involvement.
Grading Criteria:
Grade 1: Minimal neutrophil infiltration
Grade 2: Moderate infiltration with microabscesses
Grade 3: Extensive infiltration with tissue necrosis
Based on neutrophil density and tissue destruction.
Immunohistochemistry
Positive Markers:
CD15 (neutrophils)
Myeloperoxidase (neutrophils)
CD68 (macrophages, if present)
Complement components (C3, C5a)
Bacterial antigens (organism-specific)
Fibrinogen (fibrin deposition).
Negative Markers:
CD3 (T-lymphocytes minimal in acute phase)
CD20 (B-lymphocytes absent)
CD138 (plasma cells absent)
Viral antigens (typically negative).
Diagnostic Utility:
CD15 confirms neutrophilic nature
Bacterial immunostains identify organisms
Distinguishes from chronic villitis
Quantifies inflammatory response
Aids in organism identification.
Molecular Subtypes:
Listeria monocytogenes (gram-positive rods)
Group B Streptococcus
E
coli
Enterococcus species
Staphylococcus aureus
Mixed bacterial infections.
Molecular/Genetic
Genetic Mutations:
No specific genetic mutations
Host immune response genes affect severity
Complement system variants
Toll-like receptor polymorphisms
Cytokine gene variants.
Molecular Markers:
Bacterial DNA by PCR
16S rRNA sequencing for organism identification
Inflammatory markers (IL-1β, TNF-α, IL-6)
Complement activation products
Neutrophil activation markers.
Prognostic Significance:
High risk of fetal infection
Maternal sepsis risk
Preterm delivery association
Risk of fetal death
Long-term neurodevelopmental sequelae
Chorioamnionitis development.
Therapeutic Targets:
Immediate antibiotic therapy
Broad-spectrum coverage initially
Organism-specific therapy after identification
Maternal supportive care
Fetal monitoring and delivery timing
NICU preparation.
Differential Diagnosis
Similar Entities:
Chronic villitis (lymphocytic infiltrate)
Chorioamnionitis (membrane inflammation)
Funisitis (cord inflammation)
Maternal floor infarction
Villous infarction without inflammation.
Distinguishing Features:
Acute villitis: Neutrophil predominance
Acute villitis: <1 week duration
Chronic villitis: Lymphocyte predominance
Chronic villitis: >1 week duration
Chorioamnionitis: Membrane involvement
Funisitis: Cord vessel involvement.
Diagnostic Challenges:
Early recognition before microabscess formation
Organism identification
Distinguishing from other acute inflammatory conditions
Sampling adequacy
Correlation with clinical presentation.
Rare Variants:
Necrotizing villitis
Hemorrhagic villitis
Mixed acute and chronic villitis
Fungal villitis (rare)
Viral villitis with secondary bacterial infection.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
Placenta weighing [weight]g showing acute inflammatory changes with [distribution]
Diagnosis
Acute Villitis (Neutrophilic Villitis)
Classification
Classification: Grade [1/2/3] acute villitis with [focal/diffuse] distribution
Histological Features
Shows dense neutrophilic infiltrate in villous stroma with microabscess formation
Organism Studies
Gram stain: [results], Special stains: [results], Organisms: [identified/pending culture]
Severity Assessment
Severity: Grade [1/2/3] based on neutrophil density and tissue destruction
Clinical Correlation
Findings consistent with acute bacterial infection. High risk for maternal and fetal complications.
Recommendations
Immediate antibiotic therapy recommended. Culture correlation essential. NICU involvement advised.
Final Diagnosis
Acute Villitis, Grade [1/2/3], with [organism/pending identification]