The concept of [overview] simple hydrocephalus refers to the excessive accumulation of cerebrospinal fluid in the skull. The site is often intracerebroventricular and can also involve the subarachnoid space. However, this concept does not reflect the accumulation of cerebrospinal fluid due to a decrease in brain tissue and hydrocephalus due to impaired cerebrospinal fluid dynamics. Cerebrospinal fluid kinetic disorders are defined as accumulation of cerebrospinal waves due to any disorder in the production or absorption of cerebrospinal fluid. If the hydrocephalus is due to an obstruction of the cerebrospinal fluid circulation channels, which causes its absorption to be impaired, i.e., the ventricular system cannot adequately communicate with the subarachnoid space, it is called non-traffic hydrocephalus. If the obstruction is outside the ventricular system, the subarachnoid space or the end point of cerebrospinal fluid absorption. It is called ventromedial hydrocephalus, also known as non-obstructive hydrocephalus. According to the anatomical site of cerebrospinal fluid accumulation, we call it internal hydrocephalus if the cerebrospinal fluid accumulates solely in the ventricles, and external hydrocephalus if the fluid accumulates in the subarachnoid space on the cortical surface. Acute, subacute and chronic hydrocephalus can be classified according to the length of clinical onset and the severity of symptoms. In general, the course of acute hydrocephalus is within one week. The course of subacute hydrocephalus is within one month, and the course of chronic hydrocephalus is more than one month. According to the presence or absence of clinical symptoms, it can be divided into symptomatic hydrocephalus and non-symptomatic hydrocephalus. Some scholars have also tried to classify hydrocephalus by reflecting the pathophysiological process of hydrocephalus. The former means the enlargement of the ventricles that is caused by certain pathogenic factors and no longer develops, while the latter means the progressive development of the enlargement of the ventricles and causes diffuse and chronic atrophy of the cerebral cortex. [Clinical manifestations] The symptoms of hydrocephalus include headache, nausea, vomiting, ataxia and blurred vision. Headache is most common with bilateral frontal pain. As the cerebrospinal fluid reflux is less when lying down, so the headache is heavier after lying down or in the morning, and can be relieved when sitting down. Nausea and vomiting are often accompanied by headache. It is characterized by vomiting in the morning when the headache is severe, which can be distinguished from vestibular vomiting, and ataxia is mostly trunk-related, with unstable standing, wide foot spacing. Large stride length. In contrast, hydrocephalus produced by cerebellar hemisphere lesions manifests limbic ataxia. Visual impairment, including blurred vision, loss of vision and diplopia from abducens nerve palsy, may be present in later stages with recent memory impairment and general discomfort. Optic papilloedema is an important sign of cranial hypertension, and abducens nerve palsy suggests intracranial hypertension without localizing the diagnosis. Hydrocephalus itself can be a component of somatic ataxia and may indicate cerebellar earthworm lesions. Other focal signs may indicate a specific lesion location. [Treatment and prognosis] Surgery is the only definitive and effective treatment for hydrocephalus. There are two surgical approaches: ventriculoscopic triple ventriculostomy and ventriculoperitoneal shunt. Ventriculoperitoneal shunts are currently used only for traffic hydrocephalus because of the complications such as prolonged intraventricular placement and obstructive tubes and intracerebroventricular infection and abdominal infection, while ventriculoscopic triple ventriculostomy is currently performed for obstructive hydrocephalus. This method has become the main method for treating hydrocephalus because of the absence of risk of intra-ventricular infection in the obstructed canal and the small injury and short postoperative recovery time compared with shunt.