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You are watching: Which of the following is not a function of cerebrospinal fluid (csf)?

StatPearls . Treasure Island (FL): StatPearls Publishing; 2021 Jan-.


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Introduction

Cerebrospinal fluid (CSF) is an ultrafiltprice of plasma consisted of within the ventricles of the brain and also the subarachnoid spaces of the cranium and also spine.<1> It performs necessary features, consisting of providing nourishment, waste removal, and also protection to the brain.<2> Adult CSF volume is estimated to be 150 ml, with a distribution of 125 ml within the subarachnoid spaces and also 25 ml within the ventricles. CSF is predominantly secreted by the choroid plexus through other sources playing a much more poorly defined role. In the adult populace, its secretion varies in between individuals, commonly varying from 400 to 600 ml per day. The continuous secretion of CSF contributes to finish CSF rebirth 4 to 5 times per 24-hour period in the average young adult. The reduction of CSF turnover might add to the build-up of metabolites viewed in aging and neurodegenerative conditions. The composition of CSF is strictly regulated, and also any variation can be useful for diagnostic purposes.<1>


Cellular

Seventy to eighty percent of CSF manufacturing is through a network of modified ependymal cells known as the choroid plexus (CP).<1> The CP is a extremely specialized, simple, cuboidal epithelium continuous with ependymal cells lining the ventricles of the brain. This basic cuboidal epithelium surrounds clusters of fenestrated capillaries permitting for the filtration of plasma.<3> CP cells have actually thick microvilli current on their apical surchallenge. They are interassociated by means of tight junctions, producing a blood-CSF barrier that helps control the complace of CSF.<1>

As tbelow is no appreciable obstacle in between the CSF and also the extracellular room of the brain (ECSB), the blood-CSF obstacle additionally serves to regulate the setting of the brain.<2> Larger substances such as cells, protein, and also glucose are not enabled passage, whereas ions and also little molecules such as vitamins and nutrients deserve to pass into the CSF fairly easily.<4> Water is enabled passage via the CP epithelium via epithelial AQP1 networks. Substances that might not pass via the blood-CSF obstacle, however are needed by the brain deserve to be proactively synthesized by or proactively transported with the CP epithelial cells into the CSF. A 5-mV lumen positive voltage potential is existing throughout CP epithelial cell membranes. This electric potential distinction pulls sodium, chloride, and bicarbonate ions from the plasma into the CSF, producing an osmotic gradient which then drives the activity of water into the CSF.<3> 

When compared to plasma, CSF has actually a higher concentration of sodium, chloride, and also magnesium, yet a lower concentration of potassium and also calcium.<1> Unprefer plasma, CSF has actually only trace amounts of cells, protein, and also immunoglobulins.<2> No cells deserve to pass through the blood-CSF barrier, although tiny numbers of white blood cells are normally presented to the CSF instraight. The normal cell count of CSF is mainly reduced than 5 cells/ml.<1> In spite of alters in blood complace and also circulation, the composition of CSF is retained constant, which provides a stable intraventricular environment, crucial for keeping normal neuronal attribute.<3>


Function

CSF assists the brain by offering protection, nourishment, and also waste removal. CSF offers hydromechanical defense of the neuroaxis via 2 mechanisms. First, CSF acts as a shock absorber, cushioning the brain against the skull. Second, CSF enables the brain and also spinal cord to become buoyant, reducing the efficient weight of the brain from its normal 1,500 grams to a a lot lesser 50 grams. The reduction in weight lessens the force used to the brain parenchyma and cerebral vessels in the time of mechanical injury. Another function of CSF is to maintain homeostasis of the interstitial liquid of the brain. A secure environment for brain parenchyma is imperative for maintaining normal neuronal feature. 

The significant conduit of nutrient supply to the brain is the CP-CSF-ECSB nexus. Substprices needed by the brain are transported from the blood, via the CP, into the CSF, and also then diffusage right into the ECSB for transport to their sites of action within the brain. CSF also assists in the removal of brain metabolism waste commodities, such as peroxidation products, glycosylated proteins, excess neurotransmitters, debris from the lining of the ventricles, bacteria, virsupplies, and otherwise unnecessary molecules. Accumulation of such unvital molecules, checked out in aging and some neurodegenerative diseases, interferes through neuronal functioning of the brain. The disruption of cerebral physiology knowledgeable via the disruption of the hydrodynamics or composition of CSF says the importance of CSF functioning.<1><2><3>


Mechanism

CSF is consistently secreted through an unchanging complace, functioning to keep a stable environment within the brain.<3> CSF is driven along the neuroaxis from the site of secretion to the website of absorption, mainly by the rhythmic systolic pulse wave within the choroidal arteries. Lesser determinants of CSF circulation are frequency of respiration, posture, venous pressure of the jugular vein, the physical effort of the individual, and time of day.<2>

CSF is secreted by the CPs located within the ventricles of the brain, via the two lateral ventricles being the major producers. CSF flows throughout the ventricular device unidirectionally in a rostral to caudal manner. CSF produced in the lateral ventricles travel via the interventricular foramina to the third ventricle, via the cerebral aqueduct to the fourth ventricle, and also then with the median aperture (additionally well-known as the foramales of Magendie) right into the subarachnoid space at the base of the brain. Once in the subarachnoid room, the CSF starts to have actually a gentle multidirectional flow that creates an equalization of complace throughout the CSF. The CSF flows over the surface of the brain and dvery own the length of the spinal cord while in the subarachnoid room. It leaves the subarachnoid area with arachnoid villi uncovered alengthy the premium sagittal venous sinus, intracranial venous sinuses, and around the roots of spinal nerves.

Arachnoid villi are protrusions of arachnoid mater with the dura mater into the luguys of a venous sinus. A 3 to 5 mmHg push gradient between the subarachnoid area and also venous sinus pulls CSF into the venous outcirculation mechanism with the arachnoid villi that aid in its absorption. CSF might likewise enter into the lymphatic system by means of the nasal cribriform plate or spinal nerve roots. The clearance of CSF is dependent upon the posture of the individual, press differentials, and also pathophysiology.<1><2>


Related Testing

Lumbar puncture (LP), also known as a spinal tap, is a typically percreated invasive procedure in which CSF is removed from the subarachnoid space. LP is used in the measurement of intracranial press and also the sampling of CSF. It is frequently suggested in the testimonial of acute headaches and infections of the central nervous device. During an LP, the patient is inserted in the lateral recumbent place. A sterile spinal needle is then gradually placed in between vertebrae, commonly at the level of L3/4 or L4/5, into the subarachnoid room. Needle insertion might be guided by fluoroscopy or ultrasound to boost success prices and alleviate the incidence of trauma. 

Once CSF starts to circulation with the needle, it is collected serially into 4 sterile tubes. Once accumulated, CSF deserve to be analyzed for abusually present or elevated CSF components, aiding in diagnosis. For example, the presence of xanthochromia, a yellow-ovariety discoloration of CSF led to by red blood cell degeneration, suggests the possibility of a subarachnoid hemorrhage. Elevation in concentrations of immunoglobulins, termed oligoclonal bands, may indicate the presence of a systemic infection or an autoimmune disease.

Contraindications of LP incorporate raised intracranial pressure, bleeding disorders, and neighborhood skin infection. The procedure is fairly safe with seldom significant complications. Complications of LP include infection, bleeding, radicular pain, or cerebral herniation. The the majority of prevalent complication is a post-LP headache via symptoms start within 24 hrs of the procedure and frequently reresolving by day 10.<5><6>


Clinical Significance

Hydrocephalus is a pathological problem in which CSF abnormally accumulates because of enhanced CSF production, blockage of flow, or lessened absorption. The ventricles distend to accommodate elevated CSF quantities, perhaps leading to damage to the brain by pushing its tworry versus the boney skull. Hydrocephalus may be congenital or acquired. Blocked CSF flow throughout the ventricles is classified as non-communicating, or obstructive, hydrocephalus. The blockage is regularly a mass such as a tumor or an abscess situated within a foramales. Since CSF secretion is consistent, obstruction of circulation will bring about CSF develop up in front of the blockage. For example, stenosis of the cerebral aqueduct, among the the majority of prevalent causes of obstructive hydrocephalus, leads to enlargement of both lateral ventricles and the 3rd ventricle. If the circulation of CSF becomes obstructed outside the ventricles, in either the subarachnoid area or site of absorption, it classifies as interacting, or non-obstructive, hydrocephalus. 

Hydrocephalus deserve to be resulted in by genetic defects, infections, bleeding in the brain, trauma, or CNS tumors. Symptoms include headaches, convulsions, nausea, vomiting, disturbances of vision, and psychological destruction. The diagnosis is figured out with imaging techniques such as ultrasound, computed tomogram (CT), or magnetic resonance imaging (MRI) scans. The a lot of widespread therapy is shunt insertion, which diverts CSF away from the ventricles to a room of the body where it have the right to be absorbed into circulation. Endoscopic third ventriculostomy, a procedure in which a hole is created in the floor of the 3rd ventricle allowing CSF to bypass an obstruction, and cauterization of CP sections which decreases CSF manufacturing are other treatment choices.  If left untreated, hydrocephalus returns a threat of cognitive disturbances, physical disturbances, and death.<7><8>

CSF Leak is a problem in which CSF is able to escape from the subarachnoid space with a hole in the surrounding dura. The volume of CSF lost in a leak varies, varying from minute to incredibly comprehensive amounts. If the loss of CSF is excellent enough, spontaneous intracranial hypostress and anxiety (SIH) may take place. SIH most often presents through a positional headache brought about by downward displacement of the brain as a result of loss of buoyancy formerly gave by the CSF. Posterior neck stiffness, nausea, and vomiting are likewise prevalent symptoms. The incidence of SIH is approximated to be 5/100,000 each year. Womales are twice as most likely to be influenced and also have a optimal age at about 40 years.

Diagnosis is aided by typical MRI findings, such as a rise of intracranial venous volume, pituitary hyperemia, intensified pachymeninges, and descent of the brain. Many situations of SIH resolve without therapy. Conservative approaches such as bed rest, hydration, and also boosted caffeine intake may likewise be effective; but, more drastic actions might be essential. An epidural blood patch, wbelow blood is injected into the spinal epidural space, might relieve CSF hypovolemic symptoms by replacing lost CSF volume via blood volume. Surgical repair of the CSF leak through a suture or steel aneurysm clip is relatively safe and effective in giving relief.<9>

Meningitis is a problem in which the coverings of the brain become inflamed. There are 2 classifications of meningitis: aseptic and also bacterial. Aseptic meningitis deserve to outcome from agents such as fungi, drugs, and also cancer metastasis, however virsupplies reason the majority of aseptic meningitis situations. Fever, nuchal rigidity, and also photophobia are classically presenting symptoms. Diagnosis is through an analysis of CSF obtained through LP. Viral PCR analysis of CSF is valuable in diagnosing viral meningitis. Treatment is often supportive, controlling fever and also pain. Bacterial meningitis has actually a a lot reduced incidence than aseptic meningitis, however is more severe. However before, the incidence of bacterial meningitis has considerably dropped as a result of regimen vaccination.

Symptoms are comparable to aseptic meningitis, however clinical presentation is even more severe. Additional symptoms encompass transformed mental standing, seizures, and also focal neurologic indications. Diagnosis is likewise possible via LP. CSF is normally cloudy in appearance through a low glucose level and potential positive gram stain and culture. Patients presumed to have bacterial meningitis have to immediately get broad-spectrum antibiotics to prevent clinical degradation. After culture outcomes rerevolve, the clinician have the right to make adjustments to the antibiotics. Patients should better be admitted to the extensive treatment unit for close monitoring. Many patients through bacterial meningitis that get appropriate therapy recoup without complications.<10>

Subarachnoid Hemorrhage (SAH) is the leakage of blood into the subarachnoid room wbelow it mixes via CSF. Trauma is the most common reason of SAH via 80% of nontraumatic SAHs resulting from aneurysm rupture. Other nontraumatic reasons of SAH incorporate arteriovenous malformations and also vasculitis. Spontaneous SAH has a low incidence, through only 30,000 situations international every year. Ninety-seven percent of patients with SAH existing via a sudden onset headache, defined as a thunderclap headache or the worst headache of the patient"s life. Other symptoms incorporate vomiting, seizures, loss of consciousness, and death. Non-contrast head CT is beneficial in diagnosis. CT has high sensitivity after hemorrhage, however sensitivity decreases as time passes. After a negative CT, an LP have to follow to dominance out SAH. An LP is positive when erythrocytes are current in tubes 1 and also 4, or xanthochromia is visible. Management of SAH consists of reducing risks of re-bleeding and also preventing any kind of additional brain injuries.<11> 

Pseudotumor Cerebri Syndrome (PTCS) is a rare medical condition in which intracranial push is elevated without the occurrence of ventriculomegaly or intracranial masses. The pathogenesis is not well taken. The a lot of extensively welcomed theory proposes diminished absorption of CSF at the arachnoid granulations or the olfactory lymphatics as the reason. This problem has an annual incidence rate of 0.9/100,000 in the general populace. Before puberty, both females and males are equally influenced, however after puberty, women are influenced nine times even more often.

PTCS many frequently affects obese womales of childbearing age. Womales in between the periods of 20 to 44 years and also who weigh 20% more than their right body weight have an incidence rate of 19.3/100,000. A spinal fluid examination is critical in the diagnosis of PTCS. CSF pressure is better than 250 mm CSF in adults and also 280 mm CSF in kids. Adolescents are the embraced worths for diagnosis of PTCS. Headache is the most prevalent presenting symptom, though tright here are no specific distinguishing attributes of a PTCS headache. Occasionally asymptomatic patients present via papilledema detected during routine eye exams. Pulsatile tinnitus, transient visual obscurations, visual area defects, and also visual loss are various other symptoms of PTCS.

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Traditional therapy consists of medications to decrease CSF secretion from the choroid plexus. Surgery is suggested for patients through worsening vision brought about by papilledema. Surgical choices encompass optic nerve sheath fenestration and CSF ssearching. Many patients through PTCS have a great outcome, although a tiny percent of patients proceed to endure persistent headaches or blindness.<12>