Obstructive hydrocephalus (non-traffic hydrocephalus (obstructive hydrocephalus): caused by obstruction of the ventricular system, the site of obstruction is mostly at the narrowing of the ventricular system, such as the interventricular foramen, the aqueduct or the exit of the fourth ventricle, etc. The ventricular system below the obstruction can be significantly enlarged). Traffic hydrocephalus (traffic hydrocephalus (there is no obstruction between the ventricles and the subarachnoid space, the site of obstruction is more distal after the cerebral crest fluid flows out of the ventricles, mostly in the basal area; the cerebral crest fluid can flow to the occipital pool and the crestal subarachnoid space, but cannot reach the subarachnoid space on the curtain, i.e., the surface of the cerebral bulb, so that the cerebral crest fluid cannot be absorbed by the arachnoid granules). Classification according to pressure High-pressure hydrocephalus Normal pressure hydrocephalus Three, classification according to time Acute hydrocephalus (days) Sub-acute hydrocephalus (weeks) Chronic hydrocephalus (months to years) Four, classification according to age Infantile hydrocephalus Older children and adults hydrocephalus Five, classification according to location Intracerebroventricular hydrocephalus Extracerebroventricular hydrocephalus (subarachnoid enlargement) In addition, there are some rare causes also caused by hydrocephalus, such as the crestal fluid overproduction caused by hydrocephalus. For example, hydrocephalus caused by hypersecretion of cerebral crest fluid, mostly seen in choroid plexus papilloma. An even rarer cause is obstruction of the superior sagittal sinus, which leads to hydrocephalus due to impaired absorption of cerebral crest fluid.