The occipital pool is an anatomical structure in the brain that is located below the cerebellum, in the lower posterior part of the posterior cranial fossa, and can be connected upward to the fourth ventricle. The greater occipital pool refers to the enlargement of the occipital pool compared to normal. The presence or absence of the occipital pool, how it is shaped and its size are different in different people, especially the shape and size, which often varies. The general enlargement of the greater occipital pool can be seen at any age, it is more of an imaging term than a disease, and in most cases is due to arachnoid cysts. Patients generally have normal volume and morphology of the fourth ventricle, no obvious occupying effect, and no hydrocephalus, etc. They do not need to be treated, and can be reviewed with semi-annual cranial MRI and followed up, and if there is continued enlargement of the occipital pool or a compressive effect, surgery is considered.