A clear, watery fluid that flows around spinal cord and brain and helps in providing protection to them is known as cerebrospinal fluid or CSF. And the test required checking the CSF is known as cytology. The cytology is a method of analysis or tests which evaluates the substance of CSF and help in diagnosing the conditions affecting the brain and the central nervous system. Choroid plexus is a special tissue that has many blood vessels helps in forming the CSF and also in secreting it. Its rate of production gives us an idea that CSF is replaced every hour in our body.