Definition/General
Introduction:
Normal cerebrospinal fluid (CSF) is a clear, colorless fluid in CNS cavities
Total volume approximately 120-150 mL in adults
Continuously produced by choroid plexus
Circulates through ventricular system
Absorbed by arachnoid granulations.
Origin:
Produced by choroid plexus (70%) in lateral, third, and fourth ventricles
Ependymal surfaces (20%)
Cerebral capillaries (10%)
Production rate: 20 mL/hour or 500 mL/day
Complete turnover every 6-8 hours.
Classification:
Normal CSF characteristics: Clear and colorless
Cell count <5 cells/μL
Protein <45 mg/dL
Glucose 50-80 mg/dL
Opening pressure 70-180 mmH2O
Sterile under normal conditions.
Epidemiology:
Present in all healthy individuals
Age-related variations minimal
No gender differences
Premature infants may have slightly higher cell counts
Elderly may have slightly higher protein.
Clinical Features
Presentation:
Normal CSF causes no clinical symptoms
Normal neurological examination
No signs of increased intracranial pressure
No fever or systemic illness
Normal mental status.
Symptoms:
No symptoms in normal state
Normal cognitive function
No headache
No nausea or vomiting
No photophobia
No neck stiffness.
Risk Factors:
No risk factors for normal CSF
Physiological state
Age variations within normal limits
No pathological processes
Intact blood-brain barrier.
Screening:
Lumbar puncture performed only for clinical indications
No routine screening of normal CSF
Diagnostic LP when CNS pathology suspected
Therapeutic LP for specific conditions.
Master Normal CSF Pathology with RxDx
Access 100+ pathology videos and expert guidance with the RxDx app
Gross Description
Appearance:
Normal CSF is crystal clear and colorless
Water-like consistency
No turbidity or cloudiness
No blood or xanthochromia
Odorless.
Characteristics:
Opening pressure 70-180 mmH2O
Specific gravity 1.004-1.007
pH 7.35-7.45
Osmolality 280-300 mOsm/kg
Protein <45 mg/dL.
Size Location:
Total volume 120-150 mL in adults
Lumbar CSF obtained at L3-L4 or L4-L5 level
Ventricular CSF has slightly different composition
Cisternal CSF intermediate composition.
Multifocality:
Present throughout entire CNS
Lateral ventricles
Third and fourth ventricles
Subarachnoid space
Central canal of spinal cord.
Microscopic Description
Histological Features:
Normal CSF contains very few cells (<5 cells/μL)
Predominantly lymphocytes (60-70%)
Monocytes (30-40%)
Rare neutrophils (<2%)
No RBCs in normal CSF.
Cellular Characteristics:
Small lymphocytes with round nuclei
Mature monocytes with kidney-shaped nuclei
Rare large lymphocytes
No atypical cells
No microorganisms visible.
Architectural Patterns:
Dispersed single cells
No clustering
Clean background
No debris or protein precipitate
Rare reactive changes.
Grading Criteria:
No grading applicable
Cell count <5/μL
Differential count: lymphocytes 60-70%, monocytes 30-40%
No atypical features.
Immunohistochemistry
Positive Markers:
CD3 positive T-lymphocytes
CD20 positive B-lymphocytes (fewer)
CD68 positive monocytes/macrophages
CD45 pan-leukocyte marker.
Negative Markers:
Cytokeratins (no epithelial cells)
GFAP (no astrocytes in normal)
Neurofilament (no neurons)
Tumor markers negative.
Diagnostic Utility:
IHC rarely needed for normal CSF
Flow cytometry may be used for lymphocyte typing
Polyclonal lymphocyte population
Normal T:B cell ratio.
Molecular Subtypes:
Normal CSF has polyclonal lymphocytes
CD4+ and CD8+ T-cells present
No clonal populations
Normal immune surveillance.
Molecular/Genetic
Genetic Mutations:
No genetic abnormalities in normal CSF
Normal chromosome complement
No clonal gene rearrangements
Normal DNA content.
Molecular Markers:
Protein <45 mg/dL
Albumin predominant protein
IgG <4 mg/dL
Glucose 50-80 mg/dL
Lactate <2.2 mmol/L
LDH <40 U/L.
Prognostic Significance:
Normal CSF indicates no CNS pathology
Intact blood-brain barrier
No inflammatory process
No malignancy
Normal CNS function.
Therapeutic Targets:
No treatment required for normal CSF
Maintenance of normal physiology
Prevention of CNS infections
Treatment of conditions causing abnormal CSF.
Differential Diagnosis
Similar Entities:
Viral meningitis (early stage)
Partially treated bacterial meningitis
Post-ictal state
Traumatic tap (minimal blood)
Normal pressure hydrocephalus.
Distinguishing Features:
Normal: Clear, <5 cells/μL
Normal: Normal protein and glucose
Viral: Lymphocytic pleocytosis
Bacterial: Neutrophilic pleocytosis
Traumatic: RBCs present.
Diagnostic Challenges:
Very low cell counts may limit evaluation
Processing artifacts
Contamination during collection
Age-related variations
Technical factors affecting counts.
Rare Variants:
Normal CSF has no variants
Individual physiological differences
Age-related changes
Diurnal variations minimal
Position-related pressure changes.
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
CSF, volume [X] mL, clear, colorless
Opening Pressure
Opening pressure: [X] mmH2O (Normal: 70-180 mmH2O)
Appearance
Crystal clear, colorless
Cell Count
Total cell count: [X] cells/μL (<5 cells/μL normal)
Cell Differential
Lymphocytes: [X]%, Monocytes: [X]%, Neutrophils: [X]%
Biochemistry
Protein: [X] mg/dL (<45 mg/dL normal), Glucose: [X] mg/dL (50-80 mg/dL normal)
Microbiology
Gram stain: No organisms seen. Culture: [Results]
Malignant Cells
No malignant cells identified
Final Diagnosis
Normal cerebrospinal fluid
Comment
CSF findings within normal limits. No evidence of infection, inflammation, or malignancy.