CSF Flashcards
What is the total volume of CSF?
150ml
What is the daily production of CSF?
550ml
What is the turnover for CSF?
> 3.5 times
What is CSF and where is it made?
plasma controlled ultra-filtrate produced by the choroid plexus of the 4th & lateral ventricles & around blood vessels
> It is in direct communication & it is actually same as brain ECF
What is the function of CSF?
- provide mechanical support
- cushioning for the brain & spinal cord
- transport biological waste
- optimises environment for neuronal function
What forms the blood brain barrier?
Tight junctions between the epithelial cells of the capillaries & those of the colloid plexus
What is the function of the blood brain barrier?
- prevent free movement of large & hydrophilic molecules between plasma & CSF & facilitating movement of essential molecules like glucose
> Fat soluble molecules cross the barriers freely
> HCO3 and H uses carbonic anhydrase in the choroid plexus to allow their passage & regeneration as carbon dioxide and water
What factors affect blood brain barrier permeability?
- Inflammation
- Immaturity
- Toxins
- Neovascularity (trauma, tumor)
Describe the course of cerebral spinal fluid?
circulates from brain tissue & choroid plexus into the ventricles, subarachnoid space, via the lateral and medial foramina of lushka & Magendie, and arachnoid villi
What is a lumbar puncture?
when a needle is inserted into the spinal canal to collect CSF for diagnostic testing
> stringently aseptic
> tube 1- glucose
> tube 2 - chloride, protein, IgG
Note: CSF in ventricles has lower protein than in the lumbar region
What are the contraindications for a lumbar puncture?
- Raised intracranial pressure
- Infection at site
CSF analysis aids in the diagnosis of?
Subarachnoid hemorrhage
Meningitis
Demyelinating disease
Malignancy
Head injury
What clinical findings distinguish bacterial from viral menigitis?
lactate
Lactate > 3.9mmol/l = bacterial
Lactate < 2.8mmol/l = viral
Explain the presence of LDH in CSF?
LDH is normally present in CSF : <40u/L in adults or <70u/L
- differentiates traumatic tap from hemorrhage because fresh traumatic taps do not elevate LDH
What is a traumatic tap and how do you distinguish it?
occurs if the needle inadvertently has entered an epidural vein during insertion during LP
> a yellowish tinge to the CSF fluid = xanthrochromia
Describe glucose in CSF?
- Enters CSF by passive diffusion or active transport
- roughly two-thirds of plasma glucose
- Normal fasting CSF glucose is 2.2-3.9 mmol/L
Describe chloride in CSF?
- Important for TB meningitis diagnosis
- normal range is 116mmol/l - 130mmol/l
- Cl < 100mmol/l is diagnostic
Describe protein in CSF?
- Spinal fluid is an ultrafiltrate of plasma lacking HMW proteins
e.g Alpha-2 macroglobulin, IgM - protein concentration of CSF is less than 1% of plasma
> slightly higher in babies due to peremeable BBB
Describe a subarachnoid hemorrhage in CSF?
red cells are a diagnostic feature
- RBCs that have been in the CSF for >4 hrs cause yellow staining of the CSF called Xanthochromia
> indicates previous bleeding
- 2-4 hrs : RBCs lyse & release oxyhemoglobin ( pink to orange color change)
- At 12hrs : Hb metabolized to bilirubin, levels peak at 36 hrs & persist to weeks
Name other causes of xanthochromia?
- High CSF protein (>1.5g/L)
- elevated serum bilirubin
- Meningeal melanoma
- Hypercaroteinemia
- Rifampicin therapy
- Previous traumatic tap
Explain the diagnostic evidence of demyelinating disorders in CSF?
- elevated levels of basic myelin protein (BMP) from breakdown of myelin sheath with high CSF protein levels from immunoglobulins
= DDs release BMP into the CSF
> Can be used to diagnose MS even in the absence of oligoclonal bands
Note: MBP is usually < 1.5ng/ml - The IgG synthesis rate or the IgG/Albumin index is also used for diagnosis
- measure the levels of both IgG and albumin
Note : MS is associated with increased IgG synthesis rate - Oligoclonal bands seen also in lymphoma, chronic lymphocytic leukaemia, malignancies, chronic active hepatitis, rheumatoid arthritis
What is the protein index?
- assesses amount of intrathecal protein synthesis due to inflammation or other pathology
- assesses permeability of BBB in relation to increased thecal protein synthesis
> Albumin is the reference protein
> Normal CSF albumin/Serum albumin ratio is less than 9
> CSF IgG index is 0.3 to 0.8
> Greater indicates increased intrathecal synthesis
Note: IgG index = IgGcsf/IgGserum divided by ALBcsf/ALBserum
Describe possible errors in metabolism that could affect CSF?
- Glycine encephalopathy(Non ketotic hyperglycinemia) - Increased glycine synthesis
- Respiratory chain disorders - Increased CSF lactate and pyruvate
- 3-phosphoglycerate dehydrogenase deficiency - low CSF serine
- Organic acidemias - increased lactate
