cerebrospinal fluid (CSF) - Physiology, Pathology, Diagnosis and therapy

In vertebrates a clear, colourless, protein-free fluid circulating through the ventricles of the brain, the central canal of the spinal cord, and the subarachnoid space. It surrounds the brain and spinal cord, and provides them with mechanical support and nutrients. In humans, CSF is sometimes collected (by lumbar puncture) and analysed for diagnostic purposes: an excess of CSF around the brain in the fetus and young child (through overproduction or blockage within the circulating system) leads to hydrocephalus, unless it is drained off.

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).

Physiology

Cerebrospinal fluid also occupies the ventricular system of the brain and the spinal cord. It is a prime example of the separation of brain function from the rest of the body, as all CSF is generated locally in the brain. The CSF formed by the choroid plexuses in the ventricles, circulates through the interventricular foramina into the third ventricle and then via the mesencephalic duct (cerebral aqueduct) into the fourth ventricle through two lateral apertures and one median aperture.

The total amount of cerebrospinal fluid is about 140 ml, being replaced 4 to 5 times a day(Enting et al., 1998), which indicates its very active circulation. This continuous flow through the ventricular system into the subarachnoid space and finally exiting into the venous system provides somewhat of a "sink" that reduces the concentration of larger, lipoinsoluble molecules penetrating into the brain and CSF. (Saunders et al., 1999)

The CSF contains approximately 0.3% plasma proteins, also being 15 to 40 mg/dL, depending on sampling site. (Felgenhauer, 1974)

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. 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.

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 impaired CSF lymphatic transport.

Diagnosis and therapy

Cerebrospinal fluid can be tested for the diagnosis of a variety of neurological diseases.

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