Cerebrospinal fluid

Cerebrospinal fluid (CSF) is a clear and colorless fluid found in the ventricles and the subarachnoid space of the central nervous system. It is produced by the choroid plexus of the lateral, third, and fourth ventricles. The fluid is continuously created at a rate of 0.5 ml per minute, with a total volume of 150 ml in the central nervous system. Its pressure normally remains steady at around 60-150 mmH2O but can increase during activities like coughing or exercise.

The choroid plexus, made up of vascular tissue covered by a fold of pia called the tela choroidea, further covered by the ependymal lining of the ventricles. The CSF contains similar inorganic salts as plasma, approximately half the amount of glucose compared to blood, minimal protein, and a small number of lymphocytes (0–3 per cubic millimeter).

The cerebrospinal fluid serves various functions. It cushions and safeguards the central nervous system from physical trauma, provides buoyancy and support for the brain, maintains the skull’s contents (reducing volume during increases in brain or blood volume), nourishes the central nervous system, eliminates wastes from neurons, and facilitates the transport of pineal secretions to the pituitary gland.

The circulation of CSF begins with its production by the choroid plexus. It then flows from the lateral ventricle to the third ventricle through the interventricular foramen of Monroe. It subsequently reaches the fourth ventricle via the cerebral aqueduct of Sylvius and also flows through the spinal canal. The CSF leaves the fourth ventricle by passing through the foramen of Majendie and Lushka and enters the subarachnoid space. From there, it moves through arachnoid granulations into the superior sagittal sinus and ultimately drains out through the internal jugular vein along with the dural venous blood.

Hydrocephalus is a condition characterized by an abnormal increase in CSF volume within the skull, often coupled by raised CSF pressure. This can occur due to increased production of the fluid, such as in a choroid plexus tumor, or due to blockage in CSF circulation, such as inflammation leading to formation of strictures or the presence of obstructing tumors. Hydrocephalus can also be caused by diminished absorption of CSF, particularly at the level of arachnoid granulations where inflammatory exudate can block the villi, or in cases of obstruction in the superior sagittal sinus caused by venous thrombosis.