CEREBRAL CIRCULATION AND CEREBROSPINAL

FLUID [CSF]

CEREBRAL CIRCULATIONThe brain receives its

blood supply from four main arteries: the two

internal carotid arteries and the two vertebral arteries.

The clinical consequences of

vascular disease in the cerebral circulation is

dependent upon which vessels or combinations of vessels are involved.

CEREBRAL CIRCULATION

CEREBROSPINAL FLUID

The cerebrospinal Fluid [CSF] is a

clear, colorless, transparent, tissue

fluid present in the cerebral ventricles,

spinal canal, and subarachnoid spaces.

CEREBROSPINAL FLUID

CEREBROSPINAL FLUID [FORMATION]

CSF is largely formed by the choroid plexus of the lateral ventricle and remainder in the third and

fourth ventricles.

About 30% of the CSF is also formed from the ependymal cells lining the ventricles and other brain

capillaries.

The choroid plexus of the ventricles actively secrete cerebrospinal fluid.

The choroid plexuses are highly vascular tufts covered by ependyma.

FORMATION & CIRCULATION OF CSF

MECHANISM OF FORMATION OF CSFCSF is formed primarily by secretion and also by

filtration from the net works of capillaries and

ependymal cells in the ventricles called choroid

plexus.

Various components of the choroid plexus form a

blood-cerebrospinal fluid barrier that permits

certain substances to enter the fluid, but prohibits

others.

Such a barrier protects the brain and spinal cord

from harmful substances.

MECHANISM OF FORMATION OF CSF

The entire cerebral cavity enclosing the brain and spinal cord has a capacity of about 1600 to 1700

milliliters

About 150 milliliters of this capacity is occupied by cerebrospinal fluid and the remainder by the

brain and cord.

MECHANISM OF FORMATION OF CSFRate of formation:

About 20-25 ml/hour

550 ml/day in adults. Turns over 3.7 times a day

Total quantity: 150 ml:

30-40 ml within the ventricles

About 110-120 ml in the subarachnoid space [of which 75-80 ml in spinal part and 25-30 ml in the

cranial part].

MECHANISM OF FORMATIONCSF is formed at a rate of about 550 milliliters each

day,. About two thirds or more of this fluid originates as secretion from the choroid plexuses in

the four ventricles, mainly in the two lateral ventricles.

Additional small amount of fluid is secreted by the ependymal surfaces of all the ventricles and by the

arachnoidal membranes

Small quantity comes from the brain itself through the perivascular spaces that surround the blood

vessels passing through the brain.

MECHANISM OF FORMATIONSecretion by the Choroid Plexus. The choroid plexus, is a cauliflower-like growth of blood vessels covered by a thin layer of epithelial cells. Secretion of fluid by the choroid plexus depends mainly on active transport of sodium ions through the epithelial cells lining the outside of the plexus. The sodium ions in turn pull along large amounts of chloride ions because the positive charge of the sodium ion attracts the chloride ion's negative charge. The two of these together increase the quantity of osmotically active sodium chloride in the cerebrospinal fluid, which then causes almost immediate osmosis of water through the membrane, thus providing the fluid secretion.

MECHANISM OF FORMATION

Less important transport processes move small amount of glucose into the cerebrospinal fluid and both potassium and

bicarbonate ions out of the cerebrospinal fluid into the capillaries.

The resulting characteristics of the CSF are: Osmotic pressure approximately equal to that of plasma

sodium ion concentration approximately equal to that of plasma chloride ion about 15 per cent greater than in plasma

potassium ion approximately 40 per cent less glucose, about 30% less

ABSORPTION OF CSF THROUGH ARACHNOID VILLI

The arachnoidal villi are fingerlike inward projections of the arachnoidal membrane through the walls into

venous sinuses.

villi form arachnoidal granulations can protrude into the sinuses.

The endothelial cells covering the villi have vesicular passages directly through the bodies of the cells large

enough to allow relatively free flow of (1) cerebrospinal fluid, (2) dissolved protein molecules, and (3) even

particles as large as red and white blood cells into the venous blood.

COMPOSITION OF CSF

Proteins = 20-40 mg/100 mlGlucose = 50-65 mg/100 mlCholesterol = 0.2 mg/100 mlNa+ = 147 meq/Kg H2OCa+ = 2.3 meq/kg H2OUrea = 12.0 mg/100 mlCreatinine = 1.5 mg/100 mlLactic acid = 18.0 mg/100 ml

CHARACTERISTICS OF CSF

Nature:Colour = Clear, transparent fluidSpecific gravity = 1.004-1.007Reaction = Alkaline and does not

coagulateCells = 0-3/ cmmPressure = 60-150 mm of H2O, 10mmHg

The pressure of CSF is increased in standing, coughing, sneezing, crying, compression of internal Jugular vein (Queckenstedt’s sign

CIRCULATION OF CSF

Circulation: CSF is mainly formed in choroid plexus of the lateral ventricle.

CSF passes from the lateral ventricle to the third ventricle through the interventricular foramen

(foramen of Monro). From third ventricle it passes to the fourth ventricle

through the cerebral aqueduct. The circulation is aided by the arterial pulsations of the choroid

plexuses. From the fourth ventricle (CSF) passes to the sub

arachnoid space, around the brain and spinal cord through the foramen of magendie and foramina of

luschka.

CIRCULATION OF CSFLateral ventricle

Foramen of Monro [Interventricular foramen]

Third ventricle:

Subarachnoid space of Brain and Spinal cord

Fourth ventricle:

Cerebral aqueduct

Foramen of magendie and foramen of luschka

FUNCTIONS OF CSF

Cushioning effect: for CNS, it keeps CNS lubricated and protected from traumatic shockHomeostasis: CSF maintains physical environment by floating the brain and absorbing the shock, CSF maintains chemical environment by preventing toxins in blood from entering CNS.Nutritive function: It brings nutrients to brain and removes waste products from brain tissue.Diagnosis of illness: Laboratory examination of CSF reveals any illness or pathological condition e.g. hemorrhages, inflammation.

CSF AND INFLAMMATION

Increased inflammatory cells may be caused by infectious and noninfectious processes.

Polymorphonuclear cells indicate acute suppurative meningitis.

Mononuclear cells are seen in viral infections, syphilis, tuberculous meningitis, multiple

sclerosis, brain abscess and brain tumors.

CSF AND PROTEINS

Increased protein: CSF proteins may rise to 500 mg/dl in bacterial meningitis, intracranial tumors,

hemorrhage & infarction.

CSF & LOW GLUCOSE

Low glucose in CSF: This condition is seen in tuberculosis

Fungal infections

Meningeal dissemination of tumors

Glucose is consumed by leukocytes and tumor cells

BLOOD IN CSF

Blood: Blood may be spilled into the CSF by accidental puncture of a vein during entry of the

LP needle.

Such blood stains the fluid that is drawn initially and clears gradually. If it does not clear, blood

indicates subarachnoid hemorrhage.

CSF AND TUMOUR CELLS

Tumor cells indicate dissemination of metastatic or primary brain tumors in the subarachnoid

space.

The most common among the latter is medulloblastoma.

They can be best detected by cytological examination.

A mononuclear inflammatory reaction is often seen in addition to the tumor cells.

INDICATIONS OF CSF EXAMINATION

Infections: meningitis, encephalitisTumors:Administration of drugs in CSF (Therapeutic aim)Antibiotics: (In case of meningitis)AntimitoticsDiagnostic aim: Myelography, CisternographyAnesthetics are also given through the lumbar Puncture.

LUMBAR PUNCTURE

A lumbar puncture also called a spinal tap is a procedure where a sample of

cerebrospinal fluid is taken for examination.

CSF is mainly used to diagnose meningitis [an infection of the meninges].

It is also used to diagnose some other conditions of the brain and spinal cord.

LUMBAR PUNCTURE

Patient usually lie on a bed on side with knees pulled up against the chest.

It may also done with sitting up and leaning forward on some pillows. Sterilize the area. push a needle through the skin and tissues

between two vertebra, into the space around the spinal cord which is filled with CSF.

CSF leaks back through the needle and is collected in a sterile container.

As soon as the required amount of fluid is collected the needle is taken out and a plaster is

put over the site of needle entry.

LUMBAR PUNCTURE

CEREBROSPINAL FLUID

CEREBROSPINAL FLUID

CEREBROSPINAL FLUID

HYDROCEPHALUSLHydrocephalus" means excess water in the cranial

vault.

This condition is frequently divided into communicating hydrocephalus and noncommunicating hydrocephalus.

In communicating hydrocephalus fluid flows readily from the ventricular system into the

subarachnoid space,

in noncommunicating hydrocephalus fluid flow out of one or more of the ventricles is blocked.

Hydrocephalus