Diseases of the nervous system can assume life-threatening proportions. They are often not detectable by a simple blood test. However, it is possible to remove nerve fluid and examine it for changes in the laboratory.
What is cerebrospinal fluid?
The brain and spinal cord are surrounded by a water-clear fluid that is formed in the brain, where it communicates with the fluid spaces inside. That is why it is also called cerebrospinal fluid or neural fluid. It protects the sensitive structures from external influences. In the area of the lower lumbar spine (lumbar), the cerebrospinal fluid collects in a kind of reservoir that no longer contains any spinal cord and can be safely obtained at this point by puncture. The procedure is therefore also called lumbar puncture; in contrast, the term spinal cord puncture, which is used from time to time, is incorrect.
What can the spinal tap show?
There is limited exchange between the blood and cerebrospinal fluid. This so-called blood–brain barrier acts like a filter, allowing needed substances such as oxygen, carbon and water to pass through and keeping harmful substances out of the nervous system. However, with some diseases and influences such as electromagnetic radiation, the function of this barrier can be disturbed.
Conclusions about the cause of the disorder can be drawn from the color of the fluid and the type and amount of substances found in the CSF. In the laboratory, red and white blood cells, proteins – especially antibodies – sugar and lactate are determined, as well as pathogens and cancer cells if necessary. In the assessment, their composition is usually related to the blood values determined at the same time. In special laboratories, additional substances reserved for specific questions, such as interferons or copper, can be determined.
When is the cerebrospinal fluid puncture performed?
- In cases of cerebral hemorrhage, for example, after an accident or as a result of a ruptured blood vessel, red blood cells show up, and the cerebrospinal fluid is pink or red.
- In infections such as bacterial and viral meningitis or neuroborreliosis, inflammatory cells and antibodies are present.
- In brain tumors, metastases and leukemia possibly cancer cells. The nervous fluid is then often cloudy white or yellow.
- In multiple sclerosis can be detected in very many patients typical changes (so-called oligoclonal bands).
- CSF punctures are also used in sudden onset of severe headache or loss of consciousness, sometimes for the diagnosis of unclear metabolic diseases especially in childhood.
How does the examination proceed?
There is no need for special preparations of the patient. If he is very excited, he is given a medication in advance. Blood is drawn about half an hour before the puncture. For the puncture, relaxed back muscles and the widest possible intervertebral spaces are important. Therefore, the patient is in a crouching position with the lumbar spine curved. When lying down, he curls up like an embryo; when sitting, he bends his head and back as far forward as possible, with an assistant holding his shoulders from the front.
First, the puncture area is thoroughly disinfected and locally anesthetized. Then a long, thin hollow needle is inserted into the CSF space between two vertebrae. Three small portions of cerebrospinal fluid are obtained by dripping and sent to the laboratory. The needle is withdrawn, the puncture site compressed, and sealed with a band-aid. The entire procedure usually takes no more than 5 minutes The patient must be on bed rest for between 4 and 24 hours, depending on the needle used.
Are there any complications?
In principle, this is a fairly harmless, less painful procedure that is rarely associated with complications. Especially if bed rest is not observed and too little is drunk, headaches may occur 24 to 72 hours after the puncture, especially when sitting or standing, possibly with neck stiffness, vomiting and hearing loss (“postpuncture syndrome”).
Very rarely, infections or paralysis occur. Lumbar puncture is dangerous in cases of increased intracranial pressure and coagulation disorders or when taking anticoagulant medication. Then it may be performed only in rare exceptional cases.
