CSF system and blood-brain barrier. Lumbar puncture. Examination of CSF. CSF syndromes
A. Cerebrospinal Fluid (CSF) System
Definition: CSF is a clear, colorless fluid surrounding the brain and spinal cord.
Functions
- Mechanical protection (shock absorber)
- Brain buoyancy (reduces effective weight)
- Nutrient and metabolite transport
- Waste removal
- Maintains CNS homeostasis
Formation & Volume: Produced mainly by choroid plexus
- Production: ~500 mL/day
- Total volume: ~150 mL
Circulation Pathway: Lateral ventricles → Foramen of Monro → 3rd ventricle → Aqueduct of Sylvius → 4th ventricle → Foramina of Magendie & Luschka → Subarachnoid space → Arachnoid villi → Venous sinuses
Absorption: Through arachnoid granulations. Into superior sagittal sinus
B. Blood–Brain Barrier (BBB)
Definition: A selective barrier separating blood from CNS tissue.
Structure: Capillary endothelial tight junctions. Basement membrane. Astrocyte foot processes
Functions
- Protects brain from toxins and pathogens
- Maintains stable CNS environment
- Controls substance exchange
Permeability
- Easily Cross BBB: Oxygen. Carbon dioxide. Lipid-soluble substances
- Poorly Cross BBB: Proteins. Most drugs. Toxins and microorganisms
C. Lumbar Puncture (LP)
Definition: Procedure to obtain CSF from the lumbar subarachnoid space.
Site: L3–L4 or L4–L5 interspace. (below spinal cord termination)
Indications
1.Diagnostic: Meningitis. Encephalitis. Subarachnoid hemorrhage. Multiple sclerosis. Guillain–Barré syndrome
2.Therapeutic: Intrathecal drug administration. Reduction of CSF pressure
Contraindications
- Absolute: Raised intracranial pressure with mass lesion. Local infection at puncture site
- Relative: Coagulopathy. Severe thrombocytopenia
D. CSF Examination
1. Opening Pressure
- Normal: 70–180 mmH₂O
- ↑ in: meningitis, hydrocephalus, intracranial hypertension
2. Appearance
- Normal: clear, colorless
- Abnormal: Turbid → infection. Bloody → hemorrhage/trauma. Xanthochromic → old subarachnoid hemorrhage
3. Cell Count
- Normal: 0–5 lymphocytes/μL
- Pleocytosis = increased WBC
4. Protein
- Normal: 15–45 mg/dL
- ↑ in: meningitis, tumors, GBS
5. Glucose ≈ 60% of blood glucose
- ↓ in: Bacterial meningitis. Tuberculous meningitis
E. CSF Syndromes
1. Meningeal Syndrome
- Clinical: Headache. Fever. Neck stiffness. Photophobia. Vomiting
- CSF: Pleocytosis. ↑ protein
2. Bacterial Meningitis Syndrome
- CSF: Turbid. ↑ opening pressure. Neutrophilic pleocytosis. ↑ protein. ↓ glucose
3. Viral Meningitis Syndrome
- CSF: Clear. Lymphocytic pleocytosis. Mild ↑ protein. Normal glucose
4. Tuberculous / Fungal Meningitis
- CSF: Lymphocytic pleocytosis. ↑ protein. ↓ glucose
5. Subarachnoid Hemorrhage
- CSF: Bloody CSF. Xanthochromia (after hours)
6. Albuminocytologic Dissociation
- Definition: ↑ protein with normal cell count
- Typical disease: Guillain–Barré syndrome