What is Cerebral Spinal Fluid?
Our brain and spinal cord are full of a clear and colourless liquid called CSF or Cerebral Spinal Fluid. Our central nervous system comprises the brain and spinal cord. It is the central nervous system that coordinates all our activities like organ function, muscle movement, and many complex human functions such as thinking and planning. CSF is also like a cushion to protect us against sudden injury or impact to the spinal cord or brain.
If there is a leakage of this vital liquid due to some injury or surgery then it can affect many parts of our body starting from headache to visual disturbance, meningitis, etc. CSF leak allows direct communication between the brain and nasal cavity, giving viruses and bacteria a direct path into our brains. Meningitis is a serious brain infection that can occur due to a CSF leak.
We will learn what is CSF, the composition of CSF, what is normal CSF volume, CSF symptoms, and CSF treatment.
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CSF is a fluid that bathes our brain and goes to the spinal cord. CSF circulation through the brain’s ventricles provides protection from external injuries. Cerebral spinal fluid also provides nutrients to the areas where it circulates.
CSF is an ultrafiltrate of plasma having low protein content and a few cells.
CSF functions include providing nutrition to the brain, removing waste from the brain, and protecting the brain and spinal cord.
In adults normal CSF volume is estimated to be 150 ml. 125 ml of this fluid is present in subarachnoid spaces and the remaining 25 ml is inside the brain ventricles.
CSF is produced primarily by a network of blood vessels in the brain called the choroid plexus and also marginally by ependymal lining cells of the ventricles in the brain.
In adults, CSF is secreted at a varying rate ranging between 400 to 600 ml in a day.
The constant cerebral spinal fluid secretion ensures there is a complete renewal of CSF four to five times within twenty-four hours (in the average young adult).
If there is a reduction in CSF turnover, it will result in metabolites accumulation which is seen in neurodegenerative diseases and ageing.
CP (choroid plexus) that produces CSF is a highly specialised and simple cuboidal epithelium that is continuous with the ependymal cells that line the ventricles in the brain.
The epithelium surrounds groups of fenestrated (having aperture or perforations) capillaries which allows plasma filtration.
The CP cells contain dense microvilli on their apical surface (at the apex). These cells are connected to each other via tight junctions which creates a CSF-blood barrier that helps in controlling CSF composition.
Since there is no barrier between the extracellular space of the brain and CSF, this CSF-blood barrier also contributes to regulating the brain environment.
Due to this barrier, large materials like cells, glucose, protein, etc. can not enter the CSF but ions and smaller molecules like nutrients and vitamins are able to pass through this CSF-blood barrier.
The epithelial AQP1 channels allow water to pass through the CP epithelium.
CSF, compared to plasma, has a higher concentration of magnesium, chloride, and sodium but calcium and potassium are present in the CSF in low concentration.
CSF flowing in the ventricular system makes its way into the subarachnoid space and is finally absorbed in the venous system villi through the subarachnoid villi.
Few other important CSF functions are:
Protection of the brain during fluctuations in blood pressure.
Regulation of the central nervous system’s chemical environment.
As a vehicle for intracerebral transport.
CSF Leak
The outermost layer of the meninges is called the dura. When the membrane surrounding the spinal cord or brain has a tear or hole, the CSF liquid escapes. There are several causes of CSF leak as outlined below:
Some CSF leaks are spontaneous and their cause is unknown.
A trauma like a head injury.
Surgery of sinus or brain.
Lumbar puncture (also referred to as spinal anaesthesia spinal tap) can also result in CSF leak.
People who have high-pressure hydrocephalus (abnormal fluid build-up in ventricles of the brain) are also at a high risk of CSK leak.
Symptoms of CSF Leak
A CSF leak can cause any of all of the symptoms mentioned below:
Positional headache that gets worse when you sit upright and is better when lying down. This is due to intracranial hypotension.
Nasal drainage.
Nausea and vomiting.
Meningitis.
Tinnitus.
Visual disturbances.
Neck pain and stiffness of the neck.
Sensitivity to light (photophobia).
Pain between shoulder blades.
Sensitivity to sound (Phonophobia).
Hearing issues like muffled sounds or ringing in ears.
Sense of imbalance.
Metallic or salty taste in the mouth.
Ear drainage.
Sense of drainage in the back of the throat.
Anosmia (Loss of sense of smell).
Cutaneous sinus tract drainage (When the CSF fluid leaks into the sinus tract, a pathway gets created which drains out the fluid through the skin).
CSF Analysis
If you show any of the symptoms of a CSF leak, your physician may suggest a CSF analysis which is a group of tests that examine the cerebrospinal fluid for diagnosis of diseases that affect the brain and spinal cord. The other name for CSF analysis is Spinal Fluid Analysis. CSF Analysis includes tests to diagnose the following conditions:
Infectious diseases like meningitis and encephalitis that affect the brain and spinal cord can be found through CSF analysis. The test looks at bacteria, white blood cells, and other materials in the CSF for determining if the infection is present or not.
Autoimmune disorders for instance MS (multiple sclerosis) and Guillain-Barre syndrome can be determined with CSF analysis. To find out for these disorders, CSF analysis looks at certain proteins in the fluid (albumin protein and IgG/albumin).
Bleeding in the brain.
Brain tumours.
CSF is a colourless fluid in the brain ventricles and spinal cord which protects us from any kind of shock like a head injury. Because of many reasons like brain injury, surgery of spine or brain, etc. can cause this CSF to escape and give rise to many diseases like meningitis. A CSF analysis of the spinal cord can determine if the leak has caused any disease or not. In case of complications treatment of CSF leaks include conservative treatments like rest, hydration, infusion, and more invasive ones like surgery.
FAQs on Cerebral Spinal Fluid
1. What is cerebrospinal fluid (CSF) and where is it found in the human body?
Cerebrospinal fluid, or CSF, is a clear, colourless body fluid that circulates in and around the central nervous system (CNS). It is primarily found in the subarachnoid space (the area between the arachnoid mater and pia mater meninges), the ventricles of the brain, and the central canal of the spinal cord.
2. What are the main functions of cerebrospinal fluid?
The importance of cerebrospinal fluid lies in its multiple protective and metabolic functions for the brain and spinal cord. Its key functions include:
- Protection and Cushioning: CSF acts as a shock absorber, protecting the delicate brain and spinal cord from mechanical injury and trauma.
- Buoyancy: By suspending the brain, CSF reduces its effective weight from about 1,400 grams to approximately 25 grams, which prevents the brain from being crushed under its own weight.
- Waste Removal: It serves as a medium for removing metabolic waste products from the CNS, which lacks a lymphatic system.
- Nutrient and Hormone Transport: CSF helps in transporting essential nutrients and hormones to different parts of the brain.
3. Where is cerebrospinal fluid produced in the brain?
Cerebrospinal fluid is continuously produced by specialised tissue called the choroid plexus. This tissue is located within the walls of the ventricles of the brain, which are the fluid-filled cavities deep inside the brain.
4. How does cerebrospinal fluid circulate throughout the central nervous system?
The circulation of CSF follows a specific pathway. It is first produced in the lateral ventricles, flows into the third ventricle, and then passes through the cerebral aqueduct into the fourth ventricle. From there, it moves into the subarachnoid space surrounding the brain and spinal cord. Finally, it is reabsorbed back into the bloodstream through structures called arachnoid villi or granulations.
5. How is cerebrospinal fluid different from blood plasma in its composition?
While CSF is derived from blood plasma, its composition is significantly different due to the selective filtration process at the blood-CSF barrier. The main differences are:
- Protein Content: CSF has a much lower concentration of protein than blood plasma.
- Cell Count: Healthy CSF is almost completely cell-free, whereas blood is rich in red and white blood cells.
- Ion Concentrations: The concentrations of ions like sodium, potassium, calcium, and chloride are actively regulated and differ from those in plasma to maintain a stable environment for neural function.
6. What is the importance of maintaining normal CSF pressure?
Maintaining normal intracranial pressure is crucial for brain health. A disruption in the balance between CSF production and absorption can lead to serious conditions. If CSF accumulates due to a blockage or poor absorption, it can cause hydrocephalus, a condition of increased pressure that can damage brain tissue. Conversely, abnormally low CSF pressure can cause severe headaches and other neurological issues.
7. How does the blood-brain barrier relate to the formation of cerebrospinal fluid?
The blood-brain barrier (BBB) and the blood-CSF barrier work together to protect the central nervous system. While the BBB protects the brain tissue itself, the blood-CSF barrier, located at the choroid plexus, specifically regulates the formation of CSF. It filters blood plasma and actively transports specific substances to create CSF, ensuring that it is a stable, clean fluid free from toxins, pathogens, and large molecules found in the blood.
