Cerebrospinal Fluid (CSF) Overview

Introduction to Cerebrospinal Fluid (CSF)

• Definition: CSF can be likened to a specialized blood or fluid product that serves numerous critical functions in protecting the central nervous system (CNS).

  • Cushions the CNS

  • Removes waste

  • Delivers nutrients

Production and Circulation of CSF

• Source:

  • CSF is produced by the choroid plexus located in the ventricles of the brain.

  • Circulates through:

  • Brainstem

  • Spinal cord

  • Subarachnoid space

• Exit Route:

  • Enters the bloodstream via the veins of the arachnoid granulations.

Pathological Conditions Related to CSF

• Obstruction Effects:

  • Obstruction in CSF flow leads to the buildup of water in the brain, causing conditions like hydrocephalus.

  • Commonly seen in infants.

• Impact:

  • Can lead to brain trauma, stroke, or infection.

Role of CSF in Blood-Brain Barrier (BBB)

• Importance: CSF serves as a critical component for maintaining the integrity of the blood-brain barrier, characterized by:

  • Very tight junctions that prevent blood from directly accessing brain tissue.

Anatomy of Meninges and CSF Flow

• Meninges Structure:

  • Meninges consist of three layers:

  1. Dura mater

  2. Arachnoid layer

  3. Pia mater

• Flow Path: CSF flows between the arachnoid layer and the pia mater within the subarachnoid space.

CSF Collection Procedure

• Lumbar Puncture:

  • A procedure performed by a physician or anesthesiologist.

  • Aseptic Technique: Essential to prevent bacterial contamination.

  • Local anesthetic is applied to the area before puncturing the dura mater.

  • Opening and Closing Pressures: Measured before and after CSF collection.

  • Number of Tubes: Typically, CSF is collected in four different tubes, each serving different testing purposes.

Tube Functionality and Testing

1. Tube 1: Chemical testing (does not matter if contaminated by skin flora).

2. Tube 2: Microbiology testing (most sterile).

3. Tube 3: Send-out testing (viral antigen testing, electrophoresis).

4. Tube 4: Microscopic testing (to minimize inaccuracies from traumatic tap).

Handling and Processing CSF

• Critical Handling:

  • CSF should be labeled and transported to the laboratory immediately to avoid cell lysis.

  • Delays can affect cell counts and chemistry results including lactate levels.

• Low Volume Considerations:

  • Prioritize tests when low volume is collected, especially if only 1 mL of CSF is available. contact physician

CSF Examination

Physical Examination

• Normal Appearance:

  • Clear and colorless, resembling water.

• Cloudiness: Indicates the presence of cells, proteins, or microorganisms.

• Xanthochromia:

  • Definition: Abnormal color usually yellow, but can also be orange or pink.

  • Causes: May indicate past hemorrhage due to the presence of proteins and cellular debris.

Microscopic Examination

• Cell Counts:

  • Count red blood cells (RBCs) and white blood cells (WBCs) using a hemocytometer.

  • Normal white blood cell count: 0-5 WBCs.

• Differential Counts:

  • Identify types of WBCs present (neutrophils, lymphocytes, etc.).

  • done on wright stain

Analysis of Cell Types in CSF

• Neutrophils: Associated with bacterial meningitis.

• Lymphocytes: Indicative of viral infections.

• Plasma Cells: Related to multiple sclerosis (MS).

• Macrophages: Involved in cleanup from infections or hemorrhage.

• Eosinophils: Linked to parasitic infections.

• Malignant Cells: Abnormal presence could indicate tumors, leukemias, or lymphomas.

Neutrophils and Macrophages in CSF

• Macrophages: Cleanup cells that can engulf debris (including erythrophages post-hemorrhage).

• Eosinophils Presence: Indicates potential parasitic infection or allergies.

CSF Chemistry Testing

Protein Testing

• Protein Levels: Normal total protein: 15–45 mg/dL, much lower than in blood.

• Increased Proteins: Often seen in conditions like meningitis and MS, indicating barrier integrity issues.

• Specific Proteins: Assess albumin and IgG levels to determine underlying pathologies.

  • IgG Presence: Often elevated in infections and MS.

  • albumin not made in CSF, big issue ; if elevated, it suggests a disruption in the blood-brain barrier, indicating potential neurological damage or inflammation.

• CSF electrophoresis is primarily done to detect this oligoclonal banding in the gamma region. When we see this present, that's suggestive of multiple sclerosis. So the thing that I would know on this slide would definitely be this bullet point. Something else that helps us diagnose MS is myelin basic protein. So myelin is a fat like insulator that surrounds our nerves and makes nerve conduction easier.

Glucose and Lactate Testing

• Glucose Levels: Normal CSF glucose is 60-70% of blood glucose; a drop may indicate meningitis or cancer.

• could be traumatic tap, glucose in RBC’s

• Lactate Levels: Normal values range from 10-22 mg/dL;

  • Increased values suggest tissue hypoxia or anaerobic metabolism in conditions like cerebral infarction.

Microbiological Testing of CSF

• Importance in Diagnosis: Vital for determining causative agents in meningitis.

• Sterility and Temperature: Crucial for ensuring accurate results.

  • Recommended Stains: Gram stains, acid-fast staining, and India ink staining for specific pathogens(cryptococcus neoformmans). need to centrifuge first

• Culture Tests: Main method for identifying common meningitis pathogens (e.g., Haemophilus influenzae, Neisseria meningitidis).

Special Considerations in CSF Analysis

• Oligoclonal Bands: Detected through electrophoresis; indicative of multiple sclerosis.

• Presence of Myelin Basic Protein: Suggests progression of diseases affecting myelin sheaths, e.g., MS.

• PCR Testing: Emerging as a diagnostic tool for viral causes of meningitis (e.g., HSV, CMV). Being done more often

Conclusion

• Summary of Key Findings: Different cell types and biochemical tests in CSF can lead to critical insights into abnormalities affecting central nervous system health and inform the clinical approach to a variety of neurological conditions.