Cerebrospinal fluid

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Cerebrospinal fluid (CSF), Liquor cerebrospinalis, is a clear bodily fluid that occupies the subarachnoid space in the brain (the space between the skull and the cerebral cortex—more specifically, between the arachnoid and pia layers of the meninges). It is basically a saline solution and acts as a "cushion" or buffer for the cortex.

Physiology

Cerebrospinal fluid also occupies the ventricular system of the brain and the spinal cord. It is mainly produced by the choroid plexus, but also by the ependymal lining of the brain's ventricles. The CSF is formed by the choroid plexus or the ventricles, circulates through the interventricular foramina into the third ventricle and then via the mesencephalic duct (cerebbfg fg ral aqueduct) into the fourth ventricle space through two lateral apertures and one median aperture, and is then absorbed by the venous system to the blood circulation.

The total amount of cerebrospinal fluid is about 150 ml, and about 500 ml is produced every day, which indicates its very active circulation.

Pathology

The cerebrospinal fluid has many putative roles including mechanical protection of the brain, distribution of neuroendocrine factors, and facilitation of pulsatile cerebral blood flow. Understanding cardiovascular dynamics is valuable as the flow pattern of arterial blood must be tightly regulated within the brain in order to assure consistent brain oxygenation. CSF movement allows arterial expansion and contraction by acting like a spring, which prevents wide changes in intracranial blood flow. When disorders of CSF flow occur, they may therefore impact not only CSF movement, but also the intracranial blood flow, with subsequent neuronal and glial vulnerabilities. The venous system is also important in this equation. Infants and patients shunted as small children may have particularly unexpected relationships between pressure and ventricular size, possibly due in part to venous pressure dynamics. This may have significant treatment implications but the underlying pathophysiology needs to be further explored.

CSF connections with the lymphatic system have been demonstrated in several mammalian systems. Preliminary data suggest that these CSF-lymph connections form around the time that the CSF secretory capacity of the choroid plexus is developing (in utero). There may be some relationship between CSF disorders, including hydrocephalus and impaired CSF lymphatic transport.

Diagnosis and therapy

Cerebrospinal fluid can be tested for the diagnosis of a variety of neurological diseases. Usually, it is obtained by a procedure called lumbar puncture in an attempt to count the cells in the fluid and to detect the levels of protein and glucose. These parameters alone may be extremely beneficial in the diagnosis of central nervous system infections (especially meningitis and subarachnoid hemorrhage). Moreover, a cerebrospinal fluid culture examination may yield the microorganism that has caused the infection. By using more sophisticated methods, such as the detection of the oligoclonal bands, an ongoing inflammatory condition (for example, multiple sclerosis) can be recognized. A beta-2 transferrin assay is highly specific and sensitive for the detection for e.g. cerebrospinal fluid leakage.

Lumbar puncture can also be performed to measure the intracranial pressure, which might be increased in certain types of hydrocephalus.

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