Cerebrospinal fluid is a biological fluid in which the brain and spinal cord bathe. Zoom on its functions and on the diseases that can reveal its analysis.
1. Definition of cerebrospinal fluid
Cerebrospinal fluid (CSF) is a colorless fluid found in the brain and spinal canal. This cerebrospinal fluid (CSF) is distributed in two spaces: the subarachnoid space, which is external to the central nervous system (brain and spinal cord), and the ventricular system, which is located inside the brain.
The cerebrospinal fluid (CSF), which is located outside the central nervous system, forms cisterns: the large cistern under the cerebellum, the posterior cistern containing the basilar artery, and the inter-peduncular cistern containing the polygon of Willis.
The central nervous system (CNS) is surrounded by the meninges. Between the dura mater and the arachnoid, which does not penetrate the sulci, is the subdural space that contains a small amount of lymph-like fluid. The last meninges, the pie-mum, penetrates the sulci. The cerebrospinal fluid is found between the piebald and the arachnoid.
The cerebrospinal fluid is produced mainly in the choroid plexuses, but also in the capillaries of the subarachnoid, spinal and peri-brain space, and to a small extent in the intra-parenchymal vessels. It then joins the subarachnoid space through the perivascular spaces of Virchow-Robin.
The cerebrospinal fluid is a colorless fluid with a pH of about 7.32. It contains 3 to 5 lymphocytes per cm3. Its composition is different from that of plasma, although it is similar. Its volume is 150 ml in adults, of which 30 ml are in the spinal subarachnoid space.
The secretion is 500 ml per 24 hours, i.e. approximately 21 ml per hour, which means that the totality of the cerebrospinal fluid is renewed 3 to 4 times per day.
The fluid space of the brain chamber is a dynamic system under pressure. The pressure of the cerebrospinal fluid defines the intracranial pressure, the physiological value of which varies throughout life. It oscillates between 3 and 4 mmHg before one year and is between 10 and 15 mmHg in adults.
2. What is the purpose of cerebrospinal fluid?
Cerebrospinal fluid has a double role of protection (against infectious and toxic agents, trauma...) and exchange with the blood through the hematomeningeal barrier.
The cerebrospinal fluid (CSF) plays a role in the mechanical protection of the central nervous system. It prevents the brain tissue from being subjected to mechanical pressure. It acts as a fluid buffer and protection in certain positions (head down).
It acts as a buffer and as a reservoir to regulate the brain volume: if the volume of the brain parenchyma or the volume of the intracerebral blood increases, the cerebrospinal fluid is drained. If, on the other hand, the brain volume or the cerebral blood volume decreases, the cerebrospinal fluid increases.
Molecules and waste products from the brain are drained into the cerebrospinal fluid, which also plays an immunological protective role. Cerebrospinal fluid also serves to some extent for nutrient exchange with the nervous tissue.
3. What are the diseases of the cerebrospinal fluid?
The cerebrospinal fluid is transparent and its composition is relatively constant. It is modified by all inflammatory processes in the meninges. Indeed, as the cerebrospinal fluid is in intimate contact with the brain, and also with the spinal cord, its composition can be modified in many diseases, neurological or extra-neurological.
These changes may concern the biochemical composition of the cerebrospinal fluid (glucose or proteins), the presence of microbes (bacteria, viruses, or parasites), or abnormal cells (cancerous).
Increased volume due to a brain tumor decreases the cerebrospinal fluid. Chronic meningitis, spinal cord tumors, and meningeal tumors produce Froin syndrome: during spinal cord compression, compression of the spinal veins releases protein-rich blood cells and plasma; hemoglobin turns the cerebrospinal fluid yellow as it degrades.
Meningitis and encephalitis are infections of the nervous system: meningitis is an infection of the meninges, encephalitis is an infection of the brain parenchyma. Meningoencephalitis is an infection of the meninges, subarachnoid space, and brain parenchyma.
Meningitis can be viral or bacterial. It can also be caused by inflammatory autoimmune diseases (systemic lupus erythematosus, Behçet's disease, sarcoidosis) or by tumor diseases (carcinomatous meningitis).
A meningeal hemorrhage or subarachnoid hemorrhage (SAH) is defined by the irruption of arterial blood into the subarachnoid spaces, with the blood mixing with the cerebrospinal fluid. An arterial aneurysm is the leading cause of meningeal hemorrhage. Other causes are arterial dissections, cerebral and spinal cord vascular malformations, reversible cerebral vasoconstriction syndrome, cerebral venous thrombosis... In 10% of cases, meningeal hemorrhage is idiopathic (of unknown cause).
Changes in the cerebrospinal fluid composition may reflect alterations in the proximal part of the peripheral nervous system (PNS): leptomeningeal carcinomatosis, neurolymphomatosis, paraneoplastic neuropathies, Guillain-Barré syndrome...
Hydrocephalus is a disorder of the hydrodynamics of the cerebrospinal fluid causing an increase in the volume of the compartment that is not allocated to this fluid. More rarely, hydrocephalus can be attributed to hypersecretion of cerebrospinal fluid, due to obstruction of the cerebrospinal fluid outflow tract. Chronic hydrocephalus can be the result of cerebral aggression (meningitis, stroke, head trauma...) or idiopathic. It is manifested by walking and balance disorders, sphincter disorders (urinary and fecal incontinence), and cognitive disorders (memory, attention...). The accumulation of cerebrospinal fluid in the cranium can result in an increase in pressure (intracranial hypertension) that can damage the brain and alter its functioning.
4. How is the cerebrospinal fluid disease treated?
Bacterial meningitis is treated with intravenous antibiotic therapy. Mild viral meningitis is treated with rest and medication to relieve pain and fever. Meningitis due to the HIV virus requires specific antiviral treatment.
Treatment of meningeal hemorrhage due to a ruptured aneurysm, the most common cause, consists of treating the aneurysm and treating the meningeal hemorrhage itself with surgical or endovascular treatment.
The treatment of hydrocephalus is almost exclusively surgical (which consists of diverting excess cerebrospinal fluid to the heart or abdomen). Medical treatment is more limited and is aimed at reducing the secretion of cerebrospinal fluid. Treatment of the cause of the hydrocephalus is essential in parallel with any cerebrospinal fluid diversion procedure, and in particular the removal of a tumor lesion.
5. Who are the cerebrospinal fluid specialists?
Cerebrospinal fluid specialists are neurologists who take care of the treatment of nervous system pathologies: stroke, Alzheimer's disease, Parkinson's disease, epilepsy, or neurogenetic diseases. Neurosurgeons are concerned with all cranial and spinal pathologies, of tumoral, vascular, traumatic, or degenerative origin, as well as aneurysmal arterial malformations, meningeal hemorrhages, and nervous system tumors.
6. What are the cerebrospinal fluid examinations?
Cerebrospinal fluid investigations are performed by lumbar puncture, but also by gas ventriculography, myelography, CT, and MRI.
Lumbar puncture is a diagnostic method for inflammatory pathologies (infectious and non-infectious) of the brain in particular, but also of the marrow and meninges.
The analysis of cerebrospinal fluid taken by lumbar puncture is essential for the diagnosis of neurological pathologies. Its pressure can be measured: it must not exceed 15 cmH2O. Chemical analysis of the CSF (glucose albumin, lactic acid, protein electrophoresis, immunological tests), cytological (number of cells per milliliter), and bacteriological analysis can also be performed.
The indications for a lumbar puncture are infections of the central nervous system (meningitis, encephalitis, myelitis), assistance in the diagnosis of subarachnoid hemorrhage, oncology (carcinomatous meningitis, lymphoma, leukemia), inflammatory diseases (Guillain-Barré syndrome, multiple sclerosis, vasculitis, sarcoidosis). A lumbar puncture is thus essential for the diagnosis of nervous system infections such as meningitis and encephalitis. It allows the diagnosis of herpes or Creutzfeldt-Jakob disease. Cerebrospinal fluid analysis can also be used to diagnose meningeal hemorrhage, especially when the brain scan, is normal, chronic hydrocephalus, and to help diagnose certain cancers that have spread to the nervous system.
Lumbar puncture also allows the study of specific proteins in the cerebrospinal fluid, which helps in the diagnosis of certain degenerative diseases such as Alzheimer's disease. There are biomarkers in the CSF that have a sensitivity and specificity of more than 80% to detect Alzheimer's disease.
Imaging tests such as CT or MRI can be used to diagnose hydrocephalus. Brain MRI is the reference examination in case of suspicion of a brain tumor. A cerebral scanner allows the diagnosis of meningeal hemorrhage. It allows localizing of the mass, specifying its characteristics, to diagnose possible complications (involvement, hemorrhage, hydrocephalus...). In case of suspicion of meningitis, a lumbar puncture and a blood culture (blood analysis) are performed. A CT scan is performed in case of mental confusion, loss of consciousness, or if cranial hypertension is suspected.
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