Arachnoid cysts appear as relatively homogeneous and uniform hypodense shadows on cranial CT. Arachnoid cysts are encapsulated by the arachnoid membrane and located in the brain, and their interior is filled with cerebrospinal fluid. If the cyst is small, there are no clinical symptoms, while larger cysts can have a compressive and occupying effect on the surrounding area. Common sites are in the greater occipital pool, temporal pole, and pineal gland, etc. Hypointense shadows can be observed on CT in the corresponding areas with relatively uniform density and clear demarcation lines around them. When there is an occupying effect on the surrounding tissues, it may displace the surrounding tissues. For example, a large occipital pool cyst may compress the cerebellum, causing symptoms such as dizziness, unstable walking, and ataxia. In the case of hyaline septal cysts, it is possible to squeeze the lateral ventricles bilaterally, causing them to become smaller or narrower.