[Overview] Hydrocephalus is the excessive accumulation of cerebral crest fluid in the skull due to impaired balance of production and absorption of cerebral crest fluid. It is usually caused by impaired absorption of cerebral crest fluid. It can be divided into traffic and non-traffic. If the ventricular system cannot adequately communicate with the subarachnoid space due to obstruction of the cerebral crest fluid circulation channel, it is called non-traffic hydrocephalus or obstructive hydrocephalus. If the obstruction is outside of the ventricular system and causes impaired absorption in the subarachnoid space or at the end point of cerebral crest fluid absorption, it is called transport hydrocephalus, or non-obstructive hydrocephalus. [There are many causes of hydrocephalus, and the common ones are as follows: congenital malformations: stenosis of the middle cerebral aqueduct, atresia malformation of the interventricular foramen, cerebrovascular malformation, etc. Infection: intrauterine fetal infection, intracranial inflammation, obstruction of the circulatory orifice of cerebral crest fluid by proliferating fibrous tissue, occlusion of the cerebral pool, subarachnoid space and arachnoid granule adhesions. Hemorrhage: fibrous hyperplasia caused by intracranial hemorrhage, etc. Tumor: can obstruct any part of the cerebral crest fluid circulation, more commonly seen near the fourth ventricle. Others: certain hereditary metabolic diseases, perinatal and neonatal asphyxia, etc. [Clinical manifestations] Mainly include headache, nausea, vomiting, ataxia and blurred vision. Headache is most common in both frontal areas. The headache is worse after lying down or in the morning, and can be relieved when sitting. The disease progresses with painful awakening at night, persistent severe pain throughout the head, and neck pain, mostly related to the protrusion of the cerebellar tonsils into the greater occipital foramen. Nausea and vomiting are often accompanied by headache. It is not related to the position of the head and is characterized by vomiting in the morning when the headache is severe. Ataxia is mostly trunk-related, with unsteadiness in standing, wide foot spacing, and large strides. Visual impairment, including blurred vision, loss of vision, and diplopia, may be present in late patients with recent memory impairment and general malaise. Optic papilloedema is an important sign of cranial hypertension. The hydrocephalus itself may be indicative of somatic ataxia and may also indicate cerebellar earthworm lesions. Other focal signs may indicate a specific lesion location. [Treatment] There are non-surgical and surgical treatments. Non-surgical treatment is indicated in cases that cannot be treated surgically or as preoperative preparation for bypass surgery. It includes diuretics and dehydrating agents with Chinese and Western medicines. Hydrocephalus secondary to subarachnoid hemorrhage can be treated by multiple lumbar punctures. Mild hydrocephalus can be treated with non-surgical treatment first, based on dehydration therapy (mannitol) and systemic support therapy. Surgical treatment is indicated for cases with high intracerebroventricular pressure (more than 250 mm water column) or when non-surgical treatment has failed. In severe hydrocephalus, such as those with head circumference over 50 cm, cortical atrophy thickness below 1 cm, and already combined with severe dysfunction and deformity, surgical treatment is not effective. In principle, the cause of obstructive hydrocephalus should be clarified, the obstruction should be removed as much as possible, and the cause should be treated. Traffic hydrocephalus is mostly treated with cerebral crest fluid shunt. Currently, ventriculoperitoneal shunts are commonly used in clinical practice.