CSF function - nerve water for diagnosis

Diseases of the nervous system can take on life-threatening proportions. Often they are not detectable by a simple blood test. However, it is possible to remove nerve water and to examine changes in the laboratory.

What is CSF?

The brain and spinal cord are surrounded by a water-clear fluid, which is formed in the brain and communicates with the fluid spaces inside. That is why it is also called brain or nerve water. It protects the sensitive structures from external influences. In the area of ​​the lower lumbar spine (cerebrospinal fluid), the cerebrospinal fluid collects in a kind of reservoir, which contains no spinal cord, and can be safely gained by a puncture at this point. The procedure is therefore also called lumbar puncture; the occasional term spinal cord puncture is wrong.

What can the CSF function show?

There is only limited exchange between the blood and cerebrospinal fluid. This so-called blood-brain barrier acts as a filter that allows the necessary substances such as oxygen, carbon and water to pass through and keeps harmful substances away from the nervous system. However, some diseases and influences such as electromagnetic radiation may interfere with the function of this barrier.

From the color of the liquid as well as the type and quantity of the substances found in the liquor can draw conclusions on the cause of the disturbance. Red and white blood cells, proteins - especially antibodies -, sugars and lactates as well as possibly pathogens and cancer cells are determined in the laboratory. In the assessment, their composition is usually set in relation to the simultaneously determined blood values. Special laboratories can be used to determine other substances that are reserved for specific questions, such as interferons or copper.

When is the CSF performed?

  • Cerebral haemorrhages, eg after an accident or as a result of a vascular tear, show red blood cells and the nerve water is pink or red.
  • In infections such as bacterial and viral meningitis (meningitis) or neuroborreliosis, inflammatory cells and antibodies are present.
  • In brain tumors, metastases and leukemia, cancer cells may be present. The nerve water is then often cloudy-white or yellow.
  • In multiple sclerosis, typical changes can be detected in many patients (so-called oligoclonal bands).
  • CSF functions are also used for sudden severe headache or loss of consciousness, sometimes for the diagnosis of unclear metabolic diseases, especially in childhood.

How is the examination performed?

No special preparations of the patient are necessary. If he is very excited, he receives a drug in advance. About half an hour before the puncture blood is taken. For the puncture a relaxed back muscles and as far as possible intervertebral spaces are important. Therefore, the patient is in a crouching position where the lumbar spine is curved. When lying down he curls up like an embryo, while sitting he bends his head and back as far forward as possible, a helper holds his shoulders from the front.

First, the puncture area is thoroughly disinfected and locally anesthetized. Then a long, thin hollow needle is inserted between two vertebrae in the CSF space. Three small portions of nerve water are collected by dripping and sent to the laboratory. The needle is pulled out, the puncture site compressed and closed with a plaster. The entire procedure usually takes no longer than 5 minutes The patient must - depending on the needle used - between 4 and 24 hours bed rest.

Are there complications?

In principle, this is a fairly safe, less painful procedure that rarely involves complications. Especially if the bed rest is not respected and drinking too little, it can lead to headaches 24 to 72 hours after the puncture, especially while sitting or standing, possibly with neck stiffness, vomiting and hearing loss ("post-puncture syndrome").

Very rarely, infections or paralysis appear. Dangerous is a lumbar puncture with increased intracranial pressure and coagulation disorders or the intake of anticoagulant drugs. Then it may only be carried out in rare exceptional cases.

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