CSF Flashcards
Neuroendocrine role/transport function of CSF
CSF is involved in the distribution of hypophyseal hormones in the brain and the clearance of hormones from the brain and blood
Description of (normal) CSF
Clear, colorless, free of clots and free of blood
Average total CSF volume in
- Adults
- neonates
Adults = 90-150 mLs (~8% of total CNS cavity volume) neonates = 10-60 mLs
Formation of CSF
-Formed predominantly at the Choroid plexus (70%) deep within the brain/by ependymal lining the ventricles and (30%) formed as interstitial fluid.
=result of selective ultrafiltration of plasma and active secretion by the epithelial membranes
Rate of CSF formation
=500 mL/day (0.4 mL/minute) = resorption must occure
Resorption of CSF
Occurs at out-pouchings in the dura/dural sinuses called ***arachnoid villi (=granulations) that protrude through the dura to the venous sinuses of the brain and into the bloodstream.
–They act as one-way valves to maintain an excretion volume equal to the production volume–
Also, small amounts of resorption occur along the perineurial lymphatics.
Circulation of CSF
Begins in the Lateral ventricles –> 3rd ventricle –> 4th ventricle, through the ventricular foramina (three small openings in the 4th ventricle) –> Intracranial and subarachnoid spaces.
Communicating Hydrocephalus
=impaired resorption
-Usually occurs after bacterial meningitis or subarachnoid hemorrhage - CNS pressure and CSF volume ^^.
Obstructive Hydrocephalus
=blockage of any of the ventricles or the foramina
Function of the Blood-Brain Barrier
=Prevent passage of plasma constituents into CSF
Blood-Brain Barrier is composed of
Capillary epithelium and fenestrated choroidal capillaries
Factors that significantly influence a substance’s access to the brain and CSF
- Molecular weight (entry=inversely related to size)
- Protein binding (highly protein bound sub.s enter less readily than unbound sub.s)
- Lipid solubility (Lower lipid soluble sub.s enter less readily than highly soluble ones (=alcohol, CO))
Lab investigations of CSF are indicated for cases of suspected
- -Dx of disease states = Meningeal CNS infections, demyelinating diseases, CNS malignancy, hemorrhage into the CNS, and
- -Therapy
CSF specimens are obtained by
Lumbar puncture (between L3-4 or lower) using aseptic technique.
Normal pressure of CSF
= 90-180 mm/Hg - minor changes can occur due to coughing, respiration or straining.
Increased CNS pressure due to (5)
- CHF
- Inflammation of meninges
- Mass lesions
- Obstruction of intracranial venous sinuses
- Cerebral edema
Decreased CNS pressure due to (4)
- Partial/complete sinus blockage
- Circulatory collapse
- Dehydration
- CSF leakage
3-4 tubes of CSF are drawn if pressure is adequate. from first to last the tubes are used for what analysis?
1st = chemical and immunologic studies
2nd = microbiologic examination
3rd (and/or 4th) = cell count and differential
CSF may appear cloudy/turbid due (6)
- wbcs > 200 cells/uL
- rbcs > 400 cells/uL
- presence of microorganisms
- presence of contrast media
- aspiration of epidural fat during lumbar puncture
- an increased CSF protein level (>45 mg/dL)
Clots in CSF may be caused by
Increased fibrinogen, which may be due to
- traumatic tap
- subarachnoid block
- suppurative meningitis
- tuberculous meningitis (may appear on CSF in these cases after refrigeration for 12-24 hours)
Two most common causes of blood and Hgb pigments to be seen in CSF =
- Traumatic tap = artifactual presence of blood/derivatives due to interdiction of blood vessels during the lumbar puncture - As the tubes are drawn, there will be a gradual clearing.
- Subarachnoid hemorrhage = breakdown of CNS barrier and Circulatory system from trauma - All tubes collected will have the same degree of discoloration.
Traumatic tap characteristics (3)
- Clear supernatant
- (-) D-dimer (no fibrinogen)
- May have clots present
Characteristics of Subarachnoid hemorrhage (3)
- Xanthochromic supernatant
- Erythrophages on microscopic examination
- No clots
Xanthochromia
=pink, yellow or orange color of CSF supernatant
RBCs lyse in CSF due to decreased protein and lipid levels (compared to plasma) - after hemolysis, CSF will change from a cloudy/hazy pink-red –> clear pink-red, then through various shades as Oxyhgb –> Methgb –> Bilirubin (after 12 hrs).
-Decrease in discoloration over the 1st 2 days, complete clearing in 2-4 weeks. May also be due to
- CSF protein (>150 mg/dL) / TT w/ plasma contam. of protein
- Contamination by merthiolate (skin disinfectant)
- Carotenoids (hypercarotenemia)
- Melanin (Meningeal Melanosarcoma)
- Rifampin therapy
Normal cell counts in CSF
Adults =
Causes of increased segs (4)
- meningitis (***bacterial, early viral, early tuberculous)
- cerebral abscess
- post-seizure
- post-CNS hemorrhage
Causes of increased lymphs (2)
- meningitis (***viral, tuberculous, fungal, bacterial (unusual organisms))
- degenerative disorders