Cerebral Spinal Fluid in the Central Nervous System

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.