Often people who have a health checkup are told it is an arachnoid cyst and become nervous and even fearful because of it, which becomes relaxing once you are able to recognize it properly. Most people are discovered during a cranial CT, as this is now a more routine medical exam, some are discovered during other incidental examinations, and a much smaller number are found to have a spinal arachnoid cyst. Whether they are intracranial or spinal, they only differ in location, and the causes and mechanisms of occurrence and principles of management are basically the same. An intracranial arachnoid cyst is, to put it simply, an increased fluid cyst somewhere on the outside of the brain tissue, a capsule with fluid inside, specifically cerebrospinal fluid, which is the fluid that normally circulates between the brain tissue and the surface of the soft meninges that cover it and the arachnoid membrane. This fluid space is referred to in medical terminology as the subarachnoid space, and it is a very thin layer on CT and MRI images, whereas an arachnoid cyst is an increase and enlargement of cerebrospinal fluid that collects in one of these circulating places, the difference being that all of this cerebrospinal fluid is encapsulated by the wall of the capsule formed by the arachnoid membrane, so that this fluid is not in the same place as the subarachnoid space. Since the source of its contents is cerebrospinal fluid and the cyst wall is formed by the arachnoid membrane, these cysts are usually distributed on the surface of the brain and spinal cord, or in the sulci and pools of the brain, and will not be inside the brain tissue, but it will squeeze the brain tissue and occupy some space in the brain tissue. Obviously, although arachnoid cysts are also divided into primary and secondary, they are a benign occupying lesion, which is important because the vast majority of us now understand the concept of benign versus malignant, and what benign implies is relatively clear to all of us. The most common locations of cysts found on examination are in the temporal lobe, occipital greater pool, pterygoid saddle, and parietal lobe. Although arachnoid cysts may show some abnormalities due to different locations and sizes, they are usually asymptomatic or difficult to detect, but are found during physical examinations or other incidental circumstances. When an arachnoid cyst is found, the first step is not to panic and worry, but to see a neurologist to learn more about the state of the condition. In general, if the cyst is small and grows slowly and does not affect your life and work, your doctor will not recommend surgery or medication, but will let you observe it, and if it never changes, you may be able to ignore it for life. Of course, the surgery is also relatively simple.