CEREBRAL CIRCULATION AND CEREBROSPINAL FLUID [CSF]

CEREBRAL CIRCULATION AND CEREBROSPINAL FLUID [CSF] Sultan Ayoub Meo MBBS, PGC Med Ed, M.Phil, Ph.D Professor, Department of Physiology College of Medicine, King Saud University

CEREBRAL CIRCULATION TheCircle of Willis is the joining area of several arteries at the bottom (inferior) side of the brain. At the Circle of Willis, the internal carotid arteries branch into smaller arteries that supply oxygenated blood over 80% of the cerebrum.

CEREBRAL CIRCULATION

CEREBRAL CIRCULATION The Circle of Willis is a vital formation of arteries at the base of the brain OR Grouping of arteries near the base of the brain which is called the Arterial Circle of Willis. It is named after an English physician named Thomas Willis, who discovered it and then published his findings in his 1664, a seminal peace on the inner workings of the brain entitled, Cerebri anatomi (from the Latin for “Anatomy of the Brain”).

CEREBRAL CIRCULATION The brain receives its blood supply from four main arteries: the two internalcarotid arteries and the two vertebral arteries. The clinical consequences of vascular disease in the cerebral circulation is depend upon which vessels or combinations of vessels are involved.

CEREBRAL CIRCULATION The vertebral arteries unite to form Basilar artery The basilar artery and the carotids form the circle of Willis below the hypothalamus The circle of Willis is origin of six large vessels supplying the cerebral cortex Substances injected into one carotid artery distributed almost completely to the cerebral hemisphere on that side. Normally no crossing over occurs probably because the pressure is equal on both sides

CEREBRAL CIRCULATION The arteries and arterioles supply blood to the brain are highly specialized, include both vascular smooth muscle and endothelial cells that are unlike vascular cells from the peripheral circulation or other vascular beds. The vascular smooth muscle is highly responsive to changes in pressure, a process called myogenic activity,that contributes to autoregulation of cerebral blood flow. The endothelial cells in the brain circulation are also highly specialized and provide a barrier to fluid movement called the blood-brain barrier. When these normal cell processes fail or altered such as in hypertension

CEREBRAL CIRCULATION Fainting: Temporary loss of consciousness, weakness of muscles, and inability to stand up, caused by sudden loss of blood flow to the brain. Fainting is a relatively common symptom caused by a variety of problems relating to changes in blood pressure. The American Heart Association reports that fainting is responsible for 3% of all visits to emergency rooms and 6% of all admissions to hospitals.

CEREBRAL CIRCULATION Stroke: Stroke occurs when the blood supply to a part of the brain is blocked resulting in the death of an area within the brain. If a large vessel is blocked the outcome may be rapidly fatal or may lead to very severe disability. If smaller blood vessels are blocked the outcome is less severe and recovery may be good. The most common types of disability are the loss of functions of one side of the body and speech problems.

CEREBRAL CIRCULATION Principal types of stroke: Thrombotic: Stroke due to the blockage of an artery leading to or in the brain by a blood clot. Haemorrhagic: Stroke due to bleeding from a ruptured blood vessel, usually a consequence of hypertension. Embolic: Stroke due to the formation of a blood clot in a vessel away from the brain. The clot is carried in the bloodstream until it lodges in an artery leading to or in the brain. The thrombotic and haemorrhagic forms are common,

CEREBRAL CIRCULATION Transient ischaemic attack: When blood supply to a part of the brain is temporarily interrupted without producing permanent damage. Recovery may occurs within 24 hours. Usually result from small blood clots or clumps from plaques of atheroma which get carried into the blood circulation producing transient blockages. Occasionally these clots may get carried from the heart or arteries leading to the brain (e.g. carotid arteries), rather than from within the cerebral circulation itself.

CEREBRAL CIRCULATION Dementia: This may result from repeated episodes of small strokes which produce progressive damage to the brain over a period of time. The main clinical feature of dementia is a gradual loss of memory and intellectual capacity. Loss of motor function in the limbs and incontinence can also occur.

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 CSF CSF 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 from 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 CSF Rate 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 FORMATION CSF 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 FORMATION Secretion by the Choroid Plexus.The choroid plexus, is a cauliflower-like growthof blood vessels covered by a thin layer of epithelial cells. Secretion of fluid by the choroid plexus depends mainly on active transportof sodiumionsthrough 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

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 protruding 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 ml Glucose = 50-65 mg/100 ml Cholesterol = 0.2 mg/100 ml Na+ = 147 meq/Kg H2O Ca+ = 2.3 meq/kg H2O Urea = 12.0 mg/100 ml Creatinine = 1.5 mg/100 ml Lactic acid = 18.0 mg/100 ml

CHARACTERISTICS OF CSF Nature: Colour = Clear, transparent fluid Specific gravity = 1.004-1.007 Reaction = Alkaline and does not coagulate Cells = 0-3/ cmm Pressure = 60-150 mm of H2O 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 mainlyformed in choroid pleaxus 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 cerebrol aqueduct. The circulation is aided by the arterial pulsations of the chroid 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 CSF Lateral ventricle Foramen of Monro [Interventricular foramen] Third ventricle: Cerebral aqueduct Fourth ventricle: Foramen of megendie and formen of luschka Subarachnoid space of Brain and Spinal cord

CIRCULATION OF CSF Circulation: CSF slowly moves cerebromedullary cistern and pontine cisterns and flows superiorly through the interval in the tentorium cerebelli to reach the inferior surface of the cerebrum. It moves superiority over the lateral aspect of each cerebrol hemisphere.

FUNCTIONS OF CSF A shock absorber A mechanical buffer Act as cushion between the brain and cranium Act as a reservoir and regulates the contents of the cranium Serves as a medium for nutritional exchange in CNS Transport hormones and hormone releasing factors Removes the metabolic waste products through absorption

CSF AND INFLAMMATION Increased inflammatory cells [pleocytosis] may be caused by infectious and noninfectious processes. Polymorphonuclear pleocytosis indicates acute suppurative meningitis. Mononuclear cells are seen in viral infections (meningoencephalitis, aseptic meningitis), syphilis, neuroborreliosis, tuberculous meningitis, multiple sclerosis, brain abscess and brain tumors.

CSF AND PROTEINS Increased protein: CSF protein may rise to 500 mg/dl in bacterial meningitis. A more moderate increase (150-200 mg/dl) occurs in inflammatory diseases of meninges (meningitis, encephalitis), intracranial tumors, subarachnoid hemorrhage, and cerebral infarction. A more severe increase occurs in the Guillain-Barré syndrome and acoustic and spinal schwannoma.

CSF AND PROTEINS Multiple sclerosis: CSF protein is normal or mildly increased. Increased IgG in CSF, but not in serum [IgG/albumin index normally 10:1]. 90% of MS patients have oligoclonal IgG bands in the CSF. Oligoclonal bands occur in the CSF only not in the serum. The CSF in MS often contains myelin fragments and myelin basic protein (MBP). MBP can be detected by radioimmunoassay. MBP is not specific for MS. It can appear in any condition causing brain necrosis, including infarcts.

CSF & LOW GLUCOSE Low glucose in CSF: This condition isseen in suppurative tuberculosis Fungal infections Sarcoidosis 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 leptomeningeal 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. Erythrocytes from subarachnoid hemorrhage are cleared in 3 to 7 days. A few neutrophils and mononuclear cells may also be present as a result of meningeal irritation.

Leukemia Cells in CSF

CSF AND XZNTHOCHROMIA Xanthochromia [blonde color] of the CSF following subarachnoid hemorrhage is due to oxyhemoglobin which appears in 4 to 6 hours and bilirubin which appears in two days. Xanthochromia may also be seen with hemorrhagic infarcts, brain tumors, and jaundice.

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, encephalitis Inflammatory conditions: Sarcoidosis, neuro syphilis, SLE Infiltrstive conditions:Leukamia, lymphoma, carcinomatous - meningitis Administration of drugs in CSF (Therapeutic aim) Antibiotics: (In case of meningitis) Antimitotics Diagnostic aim: Myelography, Cisternography Anaesthetics are also given through the lumbar Puncture.

CONTRA-INDICATIONS FOR LP Local skin infections over proposed puncture site (absolute contraindication) Raised intracranial pressure (ICP); exception is pseudotumor cerebri Suspected spinal cord mass or intracranial mass lesion (based on lateralizing neurological findings or papilledema) Uncontrolled bleeding diathesis Spinal column deformities (may require fluoroscopic assistance) Lack of patient cooperation

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.

PRECAUTIONS FOR LUMBAR PUNCTURE • Asked to sign a consent form • Ask about taking any medicines • Are allergic to any medicines • Have / had any bleeding problems • Ask about medications such as aspirin or warfarin • Ask the female patient might be pregnant • Empty the bladder before the procedure

CEREBRAL CIRCULATION AND CEREBROSPINAL FLUID [CSF]