CSF

Question 0

CSF Formation

Answer 0

• Formed & secreted chiefly (70-75%) by choroid epithelia
• Choroid epithelia located in:
  
  • portions of the lateral ventricles
  • roofs of the third and fourth ventricles
  • foramina of Luschka and Munro (Interventricular foramen).

The choroid plexus:

• Core of capillary networks w/ fenestrated endothelia
  
  • surrounded by cuboidal, choroid epithelium.
• Separates CSF from blood in the vessels
• Secretory properties:
  
  • continuous production of CSF
  • active transport from CNS into the blood

Remaining 25-30% of CSF originates from extrachoroidal sources
-cerebral capillary walls
-Total estimated volume of CSF is about 140 ml.
*Ventricles contain ~30 ml.
*SAS of the brain and spinal cord contains ~110 ml.
Rate of formation of CSF in adults is 500 ml/day
*CSF is replaced 3-4 times per day.

Question 1

CSF Distribution and Circulation

Answer 1

• clear colorless fluid in ventricles & subarachnoid spaces (SAS)
• One-Way Direction of CSF Circulation
• Lateral ventricles thru interventricular foramina (Munro)
• Into the III ventricle & thru the cerebral aqueduct to IV ventricle
• Exits the IV ventricle laterally thru paired foramina of Lushcka
• medially through an unpaired foramen of Magendie
• foramina allow CSF into the expanded SAS called cisterns:
  
  • cerebellomedullary (magna)
  • pontine, superior (ambines)
  • interpeduncular
  • chiasmatic cistern
• drains into the superior sagittal sinus via the arachnoid villi into the venous system

Question 2

Functions of the Cerebrospinal Fluid

Answer 2

• Maintenance of constant external environment for neurons & glia
• Removal of harmful brain metabolites
  
  • one-way flow from ventricular system to SAS & venous sinuses
• Protection of CNS from trauma by the buoyancy effect
  
  • reducing the momentum of the brain to trauma

Question 3

CSF Composition

Answer 3

• not a simple filtrate or dialysate of the blood plasma.
• Protein concentration lower than in the blood plasma.
• Glucose, Ca2+, and K+concentrations are lower than in plasma.
• pH is slightly less than that of arterial blood.
• CSF contains less than 4/ml cells (monocytes & lymphocytes)
• occasional RBC in CSF from lumbar taps if the tap is contaminated by puncturing nervous tissue vessels.

Question 4

Change in CSF Color indicates:

Answer 4

Grossly bloody or yellow (xanthochromia) color may indicate a hemorrhage.

Question 5

Change in CSF Protein Content Indicates:

Answer 5

> 150 mg/dl:
-indicates bilirubin (bound to albumin) brought from the plasma to CSF

> 500 mg/dl:
-block in spinal subarachnoid space by a tumor, meningeal cancer or other compressing lesion.

Question 6

Increases in CSF White Cells Indicates:

Answer 6

• White blood cell counts > 4 /ml are pathological
• chiefly lymphocytes in fungal infections
• bacterial meningitis it is chiefly neutrophils

Question 7

Tumor Cells in CSF

Answer 7

Exfoliate tumor cells may be in the CSF in primary or metastatic brain cancer patients.

Question 8

Change in Glucose Concentration in CSF Indicates

Answer 8

Glucose in CSF is decreased in acute bacterial infection but rarely in viral infection.

Question 9

Changes in CSF gamma globulin concentration indicates

Answer 9

In multiple sclerosis (MS) and other inflammatory diseases the gamma-globulin content is increased in CSF whereas blood level of gamma-globulin is normal.

Question 10

Hydrocephalus

Answer 10

• literally ‘ water brain”
• Hydrodynamic disorder of CSF causing excess intracranial CSF
• Corrected by surgical insertion of special shunting devices.
• Characterized by an expansion of the ventricles and frequently an increase in intracranial pressure caused by:
  
  • oversecretion of CSF
  • impaired reabsorption of CSF
  • obstruction of CSF circulation (ventricles or SAS).

Question 11

Communicating hydrocephalus

Answer 11

• caused by oversecretion or impaired reabsorption
• Oversecretion can occur in tumors of the choroid plexus
  
  • papillomas
• Impaired absorption of CSF may result from tumors, congenital malformations, or scarring.

Question 12

Noncommunicating hydrocephalus

Answer 12

• caused by obstruction of CSF circulation
• Blockage at the cerebral aqueduct (tumor of pineal gland)
• Blockage the foramina of 4th ventricle (Magendie & Luschka)

Question 13

Hydrocephalus ex vacuo

Answer 13

• Occurs in aged individuals
• No increase in intracranial pressure (ICP) associated with the enlargement of the ventricles
• Thinning of cortical tissue.
• Cerebral atrophy is primary pathology

Question 14

Blood-CSF barrier:

Answer 14

• Formed by tight junctions of choroid epithelial cells
• Controls the transfer of nutrients that are needed in small amounts over an extended period of time
  
  • Eg. Vit. C, Vitamin 6, folates

Question 15

CSF-brain barrier:

Answer 15

• Interface b/t ependymal cells lining ventricles & intercelluar space of the brain/spinal cord
• No tight junctions b/t adjacent ependymal cells
• Allows molecules to move bidirectionally b/t the CSF and the intercellular space of the CNS

Question 16

Function of Blood Brain Barrier

Answer 16

• regulates diffusion of metabolites & metabolic products b/t blood and brain
• Maintains composition of the CNS microenvironment.
• Transports substances that the brain consumes rapidly
  
  • glucose, amino acids, lactate and ribonucloesides

Question 17

Structures of the Blood Brain Barrier

Answer 17

• Endothelial cells lining brain capillaries
• Tight junctions b/t adjacent endothelial cells to block diffusion.
• Endothelial cells are deficient in vesicular transport.
• Continuous basement membrane of the endothelial cells
• Perivascular foot processes of astrocytes cover the outer surface of the endothelial cells (minor role)

Question 18

Transport mechanisms for Blood Brain Barrier

Answer 18

• Diffusion for lipid soluble, hydrophobic compounds

- Passive and active transporter, ion channels & exchangers for ions & lipid insoluble hydrophilic compounds

Question 19

Circumventricular Organs

Answer 19

• Areas of specialized tissue that lack a blood-brain barrier.
• Located in close proximity to the ventricular system
  
  • Pineal body
  • Subcommissural organ
  • Subfornical organ
  • Organum vasculosum of the lamina terminalis
  • Median eminence
  • Neurohypophysis
  • Area postrema.
• Allows rapid brain response to systemic chemical changes.

Question 20

Clinical Situations that Cause the Blood Brain Barrier to Breakdown

Answer 20

• Malignant primary brain tumors and secondary brain metastases tend to have excessively leaky vessels.
  
  • Causes accumulation of interstitial fluid (vasogenic edema) -Stroke and bacterial meningitis
• MS: T lymphocytes enter the CNS thru a compromised BBB
  
  • Attack myelin in the brain & spinal cord leading to symptoms.
• Disruption by inflammation may trigger chronic or acute seizures and cause the onset of epilepsy.
• exacerbate neurological consequences of TBI, HIV-associated dementia, hypertension, brain hemorrhage, exposure to radiation and nerve gases.

Question 21

Clinical Aspect of Intentional BBB Breakdown

Answer 21

Drugs can be delivered to the brain by:

• simple diffusion
  
  • small lipid soluble molecules cross the BBB (heroin, morphine)
• temporary disruption of the BBB w/ hyperosmotic solution
• piggyback via existing membrane carriers or transcytosis of membrane receptors.
• implanted intraventricular reservoirs.

Question 22

Two Types of Brain Edema

Answer 22

-Brain edema (increased brain volume): increased water content.

Types of Brain Edema:

• Vasogenic (caused by stroke, ischemia, head trauma, meningitis)
• Cytotoxic (caused by drug poisoning, hyponatremia, water intoxication, hypoxia)