Fifth ventricle: The septum pellucidum is the septum between the lateral ventricles on both sides. A median suture forms in the primitive septum pellucidum in the fourth month of fetal life, which then develops into two separate lobules, with the fifth ventricle as the gap between the two lobules. The anterior and superior part of the cavity is the corpus callosum, the posterior and inferior part is the dome, and the lateral wall is the septum pellucidum lobule. Under normal conditions, this cavity will gradually fuse and disappear. If it has not fused by a certain age and is filled with cerebrospinal fluid, it forms a septal lumen, which is not part of the ventricular system because it does not have the ventricular canal that the latter has. The sixth ventricle: caused by incomplete closure of the hippocampus, is often formed by the posterior extension of the septal cavity or can exist alone. It is surmounted by the corpus callosum and the pressure part, and anteriorly and laterally by the vaulted column and body, which extends posteriorly and inferiorly to terminate near the foot of the vault. It is also not part of the ventricular system. Congenital hyaline septal interspace with a transverse diameter of less than 1 cm is called fifth ventricle formation, and a transverse diameter greater than 1 cm is a hyaline septal cyst. The clinical presentation is nonspecific and the cause is unclear, partly due to cystic enlargement and obstruction of the interventricular foramen or lateral ventricles causing hydrocephalus, therefore, one and the hair should be further noted for other neurological developmental abnormalities and signs. Most patients are found incidentally during cranial CT or MRI examination, mostly asymptomatic, without surgical management. However, some septal cysts grow in size with age and are associated with obvious clinical symptoms, such as headache, dizziness, poor memory, epilepsy, syncope, and so on. These patients should be treated surgically. CT, MRI: In the transverse level examination with the auditory contour, the fifth ventricle is located between the frontal angles of the lateral ventricles on both sides on the image of the upper level of the third ventricle, and its cavity wall is parallel and can reach the interventricular foramen of the lateral ventricles posteriorly. The sixth ventricle is located at the posterior end of the fifth ventricle. It is flask-shaped.