The surface of the brain and spinal cord and its interior are filled with fluid, which is called “cerebrospinal fluid” in medical terminology. In other words, the cerebrospinal fluid is distributed inside the brain and spinal cord and on their surfaces. The cavity inside the brain that is filled with cerebrospinal fluid is the “ventricle”; the cavity inside the spinal cord that is filled with cerebrospinal fluid is called the “central canal of the spinal cord”; and the cavity on the surface of the brain and spinal cord that is filled with cerebrospinal fluid is called the “subarachnoid space “. The dynamic circulation of cerebrospinal fluid has a nutritional, supportive and protective effect on the nervous system. Once the dynamic circulation of cerebrospinal fluid is broken, it can lead to an abnormal accumulation of cerebrospinal fluid, or what we call “fluid retention”. The abnormal accumulation of cerebrospinal fluid in the ventricular system is known as hydrocephalus; the abnormal accumulation of cerebrospinal fluid in the central canal of the spinal cord is known as spinal cavernous disease; the abnormal accumulation of cerebrospinal fluid in the subarachnoid space is known as arachnoid cyst. The abnormal accumulation of cerebrospinal fluid in the subarachnoid space is known as “arachnoid cyst”. Therefore, hydrocephalus, spinal cord cavitation and arachnoid cyst are essentially manifestations of impaired cerebrospinal fluid circulation.