This blog submission brings us to the close of Brain Awareness Week. As a follow up to the previous article on the anatomy and physiology of the brain, we would like to continue our learning and explore the terms we so often hear when dealing with hydrocephalus. These definitions are taken from our various educational publications, which are all found primarily under the Education and Support section of our website.
Cerebrospinal Fluid Circulation and Absorption
CSF is formed within the ventricles by small, delicate tufts of specialized tissue called the choroid plexus. The solid arrows in the drawing below, Cerebrospinal fluid (CSF) Circulatory Pathway, show the major pathway of CSF flow. Beginning in the lateral ventricles, CSF flows through two passageways into the third ventricle. From the third ventricle it flows down a long, narrow passageway (the aqueduct of Sylvius) into the fourth ventricle. From the fourth ventricle it passes through three small openings (foramina) into the subarachnoid space surrounding the brain and spinal cord. CSF is absorbed through blood vessels over the surface of the brain back into the bloodstream. Some absorption also occurs through the lymphatic system. Once in the bloodstream, it is carried away and filtered by our kidneys and liver in the same way as are our other body fluids.
The ventricular system is the major pathway for the flow of CSF. CSF also flows directly from the ventricles into the brain tissue surrounding them. This is shown by the broken arrows. Here the CSF passes through the spaces between the cells to where it eventually enters the subarachnoid space. It is believed that the brain tissue does not absorb any CSF, but simply provides another pathway for the fluid moving to the subarachnoid space. Some small amounts of CSF are also absorbed into lymphatic channels along the membranes covering the nerves (nerve sheaths) as they leave the brain stem and spinal cord .
Our bodies produce approximately a pint (500 ml) of CSF daily, continuously replacing CSF as it is absorbed. Under normal conditions there is a delicate balance between the amount of CSF that is produced and the rate at which it is absorbed. Hydrocephalus occurs when this balance is disrupted. Although there are many factors that can disrupt this balance, the most common is a blockage, or obstruction, somewhere along the circulatory pathway of CSF. The obstruction may develop from a variety of causes, such as brain tumors, cysts, scarring and infection.
To learn more about hydrocephalus, visit these areas of our website: