Hydrocephalus is one of the oldest topics in neurosurgery, having been documented as far back as 2500 years ago; it is also one of the most modern topics in neurosurgery, with no complete cure available until today. Only a proper understanding of hydrocephalus can lead to the best treatment results. In fact, hydrocephalus is not an independent disease, it is a manifestation of cerebrospinal fluid circulation disorder. A variety of diseases of the nervous system, including trauma, infection, tumor, malformation, cerebrovascular disease, etc., can lead to cerebrospinal fluid circulation disorder and manifest as hydrocephalus. Cerebrospinal fluid is a clear, colorless liquid that fills the ventricles, subarachnoid space and central canal of the spinal cord and circulates in a specific pathway to nourish, support and protect the brain and spinal cord. When abnormal accumulation of cerebrospinal fluid occurs in the ventricular system, it is called hydrocephalus; when abnormal accumulation of cerebrospinal fluid occurs in the subarachnoid space, it is called arachnoid cyst; and when abnormal accumulation of cerebrospinal fluid occurs in the central canal of the spinal cord, it is called spinal cavernous disease. Therefore, hydrocephalus, like arachnoid cysts and spinal cavernous disease, is a form of cerebrospinal fluid circulation disorder. What happens when hydrocephalus occurs? After hydrocephalus occurs, the body’s own cerebrospinal fluid circulation regulation mechanism will play a regulatory role, and according to its regulatory efficacy, there will be the following three situations: 1. The cerebrospinal fluid circulation regulation mechanism cannot effectively restore the cerebrospinal fluid circulation balance in time, and hydrocephalus becomes more and more serious, which leads to continued expansion of the ventricles, thinning of brain tissue under pressure, and impairment of whole brain function. This condition is clinically referred to as progressive hydrocephalus. Progressive hydrocephalus needs to be treated as soon as possible to relieve the brain function damage. 2. The cerebrospinal fluid circulation can reach equilibrium in a new state through its own regulation mechanism, and the ventricles no longer continue to dilate, which is clinically known as resting hydrocephalus. Clinically, we often encounter that there is no discomfort, but during physical examination or after head trauma, a cranial CT examination reveals hydrocephalus or arachnoid cyst, which often belongs to this situation. Static hydrocephalus can be observed dynamically and does not require special treatment. 3. Hydrocephalus can be relieved on its own by effective restoration of cerebrospinal fluid circulation through self-regulation of cerebrospinal fluid circulation or rehabilitation of the neurological lesion itself. This is a rare case. How is progressive hydrocephalus treated? The ideal treatment for hydrocephalus is easy to see from the causes of hydrocephalus. For hydrocephalus caused by obstruction of the cerebrospinal fluid circulation pathway, the ideal treatment is to remove the obstruction and restore normal cerebrospinal fluid circulation. For hydrocephalus caused by insufficient cerebrospinal fluid circulation power, the ideal treatment is to increase the cerebrospinal fluid circulation power. The most common method to remove obstruction in the cerebrospinal fluid circulation pathway is neuroendoscopic unblocking or fistulization of the obstructed area to restore normal cerebrospinal fluid circulation. Depending on the site of obstruction, individualized procedures are used clinically, including interventricular foraminoplasty, midbrain aqueductoplasty, hyaline septal fistula, third ventricular floor fistula, and median foraminoplasty of the fourth ventricle. Neuroendoscopy includes both rigid endoscopy and flexible endoscopy. Flexible endoscopy is more flexible and less invasive in the process of unblocking cerebrospinal fluid circulation pathways, and can perform a wider range of unblocking with better results and advantages. For cerebrospinal fluid circulation pathway obstruction caused by brain tumors, some patients can effectively restore cerebrospinal fluid circulation after tumor removal. Cerebrospinal fluid circulation power originates from the pulsation of brain tissue driven by vascular pulsation. Cerebral arteriosclerosis or large intracranial arteries due to inflammation and hemorrhage in the subarachnoid space of the skull can cause the pulsation of brain tissue to be weakened by wrapping and binding of blood vessels, which leads to cerebrospinal fluid circulation power deficiency and hydrocephalus. In addition to relieving the obstruction of the conduit, postoperative pulsation of the basilar artery acts directly on the third ventricle, which can change the power of cerebrospinal fluid circulation to a certain extent, thus relieving hydrocephalus. This is the reason why third ventricle fundoplication can be used for the treatment of some non-obstructive hydrocephalus. Neuroendoscopic surgery for hydrocephalus is similar to unblocking a drain in daily life, but requires neuroendoscopic equipment and endoscopic techniques, which are becoming more and more widely used clinically as neuroendoscopic equipment and techniques become more popular and widespread. Most patients with hydrocephalus can be relieved or controlled by the above methods, but there are still some patients who have poor surgical results due to complex obstruction of the cerebrospinal fluid circulation pathway, which is difficult to unblock comprehensively, or the cerebrospinal fluid circulation power cannot be effectively restored. Such cases can be resolved by cerebrospinal fluid shunt surgery. A cerebrospinal fluid shunt is a procedure in which cerebrospinal fluid from the ventricle is directed through a shunt into the abdominal cavity, thoracic cavity, atrium, or bladder, where the excess cerebrospinal fluid is treated. It is similar to the “South-North” project. Cerebrospinal fluid shunts are simple to perform and do not require special equipment, and can be done in hospitals above the county level in China. There are many factors that affect the success of shunt surgery. First, the shunt system must be kept open and effective. Blockage, infection, displacement or encapsulation of the shunt tube often affects the shunt effect. The second is the correct choice of shunt pressure. The choice of shunt pressure should take into account the self-regulatory mechanism of the cerebrospinal fluid circulation and correct its “out-of-compensation” part to avoid overkill and over-indulgence. The use of excessive shunts in pursuit of immediate results, resulting in lacunar ventricles, can weaken the nutritional, supportive, and protective effects of cerebrospinal fluid on brain tissue, which can also cause pain to patients. It is important to emphasize that no matter which treatment is used, it is not permanent, which means that there is a possibility of “relapse”. Endoscopic removal of cerebrospinal fluid circulation obstruction has the potential for re-infarction, and blockage of shunts after cerebrospinal fluid shunts has always troubled neurosurgeons. Therefore, hydrocephalus cannot be cured until today, and its treatment emphasizes “lifelong treatment”. If you have any special conditions after surgery, you should inform your doctor that you have had hydrocephalus surgery and get help from him/her.