We often mention the first, second, third and fourth ventricles in clinical practice, but sometimes we hear doctors say the fifth and sixth ventricles? So what are the fifth and sixth ventricles? The fifth ventricle is the septum pellucidum cavity, and the sixth ventricle is the result of incomplete closure of the hippocampal union, also known as the dome cavity, which can be formed by the posterior extension of the fifth ventricle or can exist alone. It can be caused by congenital incomplete closure of the septum pellucidum or hippocampus or by acquired trauma. If the fifth and sixth ventricles do not compress the ventricles and interventricular foramina and do not cause hydrocephalus and cranial hypertension, treatment is not necessary. If the compression of the interventricular foramen causes obstructive hydrocephalus, surgical resection and shunt are feasible; dexamethasone and acetylglutamine have also been reported to cure the disease.