CSF is a clear fluid that circulates outside of the brain, in cavities within the brain (ventricles), and in the space surrounding the spinal cord.
Most CSF originates in the choroid plexus. The choroid plexus is composed of a network of tiny blood vessels that are located in the third, lateral, and fourth ventricles. The remaining CSF, about 30%, is formed in other sites such as the subarachnoid space and the ependymal lining of the ventricles. A diagram of the brain showing the location of the choroid plexus appears on the next page of this course.
The volume of CSF in an adult is approximately 90–150 mL of CSF. Babies up to about four weeks of age have an average volume of 10–60 mL of CSF.
