Definition/General
Introduction:
Bacterial meningitis is acute purulent infection of meninges and subarachnoid space
Caused by bacterial pathogens
Characterized by neutrophilic pleocytosis in CSF
Medical emergency requiring immediate treatment
High morbidity and mortality if untreated.
Origin:
Results from hematogenous spread of bacteria
Direct extension from adjacent infections (sinusitis, otitis)
Post-neurosurgical
Traumatic CSF leak
Congenital CNS anomalies
Immunocompromised states.
Classification:
Based on age groups: Neonatal (Group B Strep, E
coli, Listeria)
Children (S
pneumoniae, N
meningitidis, H
influenzae)
Adults (S
pneumoniae, N
meningitidis)
Elderly (S
pneumoniae, Listeria)
Post-surgical (Staph, Gram-negative).
Epidemiology:
Incidence 2-10 per 100,000 annually
S
pneumoniae most common overall (50%)
N
meningitidis in young adults (25%)
Case fatality rate 10-15% with treatment
Neurological sequelae in 20-30% survivors.
Clinical Features
Presentation:
Classic triad: fever, neck stiffness, altered mental status
Rapid onset (hours to days)
Severe headache
Photophobia
Nausea and vomiting
Rash (meningococcal).
Symptoms:
Fever (95% cases)
Headache (90% cases)
Neck stiffness (85% cases)
Altered mental status (80% cases)
Nausea/vomiting (75% cases)
Photophobia (70% cases)
Seizures (30% cases).
Risk Factors:
Age extremes (<2 years, >65 years)
Immunocompromised states
CSF leaks
Recent neurosurgery
Sinusitis, otitis media
Alcoholism
Diabetes mellitus.
Screening:
Urgent lumbar puncture
Blood cultures
CT head if focal signs
Rapid antigen tests
Procalcitonin levels
Gram stain and culture.
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Gross Description
Appearance:
CSF is turbid to frankly purulent
Cloudy, milky appearance
Yellow-green tinge
Viscous consistency
High opening pressure (>300 mmH2O).
Characteristics:
Markedly elevated opening pressure (300-600 mmH2O)
High protein (100-500 mg/dL)
Very low glucose (<40 mg/dL, CSF:serum <0.4)
Very high cell count (>1000 cells/μL)
Low pH (<7.35).
Size Location:
Diffuse meningeal involvement
Subarachnoid space inflammation
Ventricular system may be involved
Cerebral edema
Increased intracranial pressure.
Multifocality:
Generalized meningitis
Basilar predominance
Ventricular involvement
Brain abscess (complication)
Subdural empyema (complication).
Microscopic Description
Histological Features:
CSF shows massive neutrophilic pleocytosis (>90% neutrophils)
Very high cell count (1000-50,000 cells/μL)
Degenerative neutrophils
Bacteria visible on Gram stain (60-90%)
Abundant debris.
Cellular Characteristics:
Mature neutrophils with multi-lobed nuclei
Degenerative changes: pyknosis, karyorrhexis
Toxic granulation
Hypersegmented neutrophils
Macrophages with phagocytosed material.
Architectural Patterns:
Sheets of neutrophils
Dense cellular infiltrate
Inflammatory debris
Fibrin strands
Bacterial colonies (when visible)
Necrotic background.
Grading Criteria:
Severity based on: Cell count >1000/μL
Neutrophil predominance >90%
Protein >100 mg/dL
Glucose <40 mg/dL
Positive Gram stain.
Immunohistochemistry
Positive Markers:
Myeloperoxidase positive neutrophils
CD15 positive neutrophils
Lysozyme positive macrophages
CD68 positive macrophages.
Negative Markers:
Lymphoid markers (CD3, CD20)
Epithelial markers
Neural markers
Tumor markers.
Diagnostic Utility:
IHC rarely needed
Gram stain most important
Bacterial culture for organism identification
Bacterial antigens by latex agglutination
PCR for fastidious organisms.
Molecular Subtypes:
Based on causative organism: Gram-positive cocci (Streptococcus, Staphylococcus)
Gram-negative diplococci (Neisseria)
Gram-negative rods (Enterobacteria)
Gram-positive rods (Listeria).
Molecular/Genetic
Genetic Mutations:
No host genetic changes
Bacterial DNA detection by PCR
16S rRNA for bacterial identification
Species-specific PCR
Resistance genes detection.
Molecular Markers:
Procalcitonin markedly elevated
C-reactive protein >100 mg/L
IL-1β, IL-6, TNF-α elevated
Lactate >4 mmol/L
LDH >100 U/L.
Prognostic Significance:
Glasgow Coma Score at presentation
Age >65 years poor prognosis
Delay in treatment worsens outcome
S
pneumoniae highest mortality
Neurological complications in 20-30%.
Therapeutic Targets:
Empirical antibiotics: ceftriaxone + vancomycin
Dexamethasone (before/with first antibiotic dose)
Targeted therapy based on culture
Supportive care
ICP management.
Differential Diagnosis
Similar Entities:
Viral meningitis (lymphocytic predominance)
Fungal meningitis (chronic, lymphocytic)
Tuberculous meningitis (lymphocytic)
Partially treated bacterial meningitis
Brain abscess rupture.
Distinguishing Features:
Bacterial: Neutrophilic predominance
Bacterial: Very low glucose
Viral: Lymphocytic predominance
TB: Lymphocytes, low glucose slowly
Partially treated: Mixed cellular pattern.
Diagnostic Challenges:
Partially treated cases may have atypical findings
Gram stain negative in 10-40% cases
Culture negative if pre-treated
Listeria may show lymphocytic predominance
Early stages may have fewer neutrophils.
Rare Variants:
Listeria meningitis (lymphocytic in elderly)
Rickettsial meningitis
Mycoplasma meningitis
Nocardia meningitis (immunocompromised)
Post-neurosurgical meningitis.
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.
URGENT NOTIFICATION
CRITICAL RESULT: Findings consistent with BACTERIAL MENINGITIS - Clinical team notified immediately
Specimen Information
CSF, volume [X] mL, turbid to purulent appearance
Opening Pressure
Opening pressure: [X] mmH2O (>300 mmH2O indicates elevated ICP)
Cell Count
Total cell count: [X] cells/μL (>1000 cells/μL)
Cell Differential
Neutrophils: [X]% (>90%), Lymphocytes: [X]%, Monocytes: [X]%
Gram Stain
Gram stain: [Positive/Negative] - [Description of organisms seen]
Biochemistry
Protein: [X] mg/dL (>100 mg/dL), Glucose: [X] mg/dL (<40 mg/dL), CSF:Serum glucose ratio: [X] (<0.4)
Culture
Bacterial culture: [Organism identified/Pending/No growth] - Sensitivity: [Pattern]
Final Diagnosis
BACTERIAL MENINGITIS - [Organism if identified]
URGENT COMMENT
MEDICAL EMERGENCY: Bacterial meningitis confirmed. Immediate antibiotic therapy and supportive care required. Infectious disease and neurology consultation recommended. Repeat LP may be needed to monitor treatment response.