Many parents of children have asked what to do if they find a cyst in their brain. Do arachnoid cysts always require surgery? What are the circumstances that require surgery and what are the ways of surgery? In order to provide parents with an objective reference and avoid unnecessary detours, I would like to give you a brief introduction to the treatment of arachnoid cysts as I understand it now. It is important to emphasize that we must not be too rash in the treatment of arachnoid cysts. We can consult more hospitals and doctors, and we should not be too superstitious about some so-called expert professors and minimally invasive, advanced technology to avoid causing unnecessary harm to our children. Intracranial arachnoid cysts (IAC) are benign lesions caused by the accumulation of cerebrospinal fluid between the two layers of the arachnoid membrane and in the subarachnoid space of the cerebral sulcus and brain pool, of which 60 to 90% occur in childhood, with the vast majority occurring on one side and the temporal lobe being more common. IAC accounts for approximately 1% of intracranial occupying lesions and occurs in a ratio of approximately 2:1 in men and women, most It is most often located on the surface of the brain tissue in the major cerebral sulci, with a supratentorial predominance, half of which are located in the lateral fissure of the middle cranial fossa. First of all, this disease is benign and although it grows in the brain and the site is important, it is not the sky is falling and it is possible to cure it. In addition, the walls of this cyst are very thin, one-fifth to one-tenth thinner than the membrane on the surface of an egg white. Also, most of the cyst is made up of cystic fluid, which is similar in composition to the rest of the fluid inside the brain, and the flow of cystic fluid to the rest of the brain after the cyst is broken does not cause any effects. IAC is mostly thought to be a congenital malformation and can also be secondary to trauma and inflammation, but the latter is less common. The formation of congenital IAC may result from alterations in CSF flow early in the formation of the subarachnoid space, or it has been suggested that it is caused by duplication of malformations and splitting during the development of the arachnoid lining. Some cases may be combined with malformations of other brain tissues and venous systems. IAC on the surface of the brain is more likely to be associated with other developmental malformations and less likely to be symptomatic at an early stage because of its location and the less important surrounding brain tissue. The vast majority of IACs are asymptomatic, are detected after trauma or on inadvertent imaging, and can remain stable for many years. However, some cases present with cyst enlargement, such as increased CSF secretion from the cyst wall, high cystic fluid protein content producing an osmotic pressure differential or the presence of live valve-like traffic in the cyst wall and subarachnoid space. Enlarged cysts can cause localized brain tissue dysplasia, epilepsy, developmental delay, visual loss or motor impairment. In addition, cysts may rupture due to trauma resulting in acute intracranial pressure increase producing symptoms such as headache and vomiting. Infants and children often present with a non-specific increase in head circumference. Therefore, many children come to our neurosurgery department with an unintentional arachnoid cyst, or because of an occasional headache, or because a CT or MRI examination reveals a cyst in the skull after a bump on the head. These cysts are usually small, have been growing for a long time, are not located in a very important area, and the child has no other discomfort. Therefore, small IACs that are unintentionally found to be asymptomatic can be treated conservatively and followed up by regular imaging examinations. A foreign scholar analyzed cases of children with enlarging IAC and concluded that cases of rapidly enlarging IAC are very rare and recommended that imaging follow-up should be considered at least 1 year after the first detection of IAC, and that imaging should be performed at any time if the child shows symptoms of rapid head circumference increase or neurological impairment. Surgery is considered for large cysts that produce brain tissue compression, hydrocephalus, or neurological symptoms due to the cyst. Currently, the indications for surgery of IAC include: (1) obvious symptoms of increased intracranial pressure, local brain tissue compression and displacement or local skull augmentation; (2) clear symptoms of neurological deficit caused by IAC or induced epilepsy; (3) supratentorial cysts of 30 ml or more than 5 cm in diameter, and large cysts that may affect brain development and intelligence; (4) intracapsular hemorrhage or combined hydrocephalus. However, recently, I have attended several academic conferences in China, and some great players suggested that even if the cysts are more than 5 cm in diameter, if the child is asymptomatic, surgery should not be recommended. My personal understanding is that if the child has reached puberty (more than 5 years old), the brain development is close to complete and there are usually no symptoms, in fact, all can be observed without considering surgery. After all, surgery is an invasive procedure with many uncertainties. Even if there is a cyst in the brain, but it does not affect the child at all, what is the harm to continue living with this cyst? The reason why I say the above paragraph is that some parents have a heavy burden in their heart and think that a cyst in the brain is very uncomfortable, so they must have surgery to cut it out, which I think is a misconception, and if the surgery fails, the damage brought to the child is hard to estimate. If surgery is really needed, how should I choose the surgery method? There is still controversy about the surgical methods for IAC, including craniotomy or neuroendoscopic opening, stereotactic aspiration and bypass surgery. The main surgical modalities are actually three: i. Craniotomy open window: This is to cut open the skull, remove part of the cyst wall under the microscope, release the cyst fluid, and communicate the cyst with the subarachnoid space or other brain pools. The advantages are: it helps to directly observe the cyst wall, it allows electrocoagulation of the arachnoid vessels, and it allows obtaining tissue specimens for pathological diagnosis. It is particularly suitable for IAC in critical areas, where placement of a shunt may result in damage to surrounding structures, or where the cyst wall may collapse. Craniotomy allows for maximal removal of the cyst wall, windowing of multifocal cysts, and easy communication with adjacent brain pools. However, this method is very invasive and prone to brain tissue collapse and cyst recurrence. Second, shunt surgery: it is also commonly known as putting a tube, which is easy to operate, has little surgical risk and good effect, can relieve intracranial hypertension and restore impaired CSF fluid dynamics, especially suitable for cases with combined hydrocephalus or cyst opening failure, and is still the most widely used treatment method. The shunt valve is mostly chosen as a low-pressure valve to ensure that it can quickly and effectively relieve symptoms and relieve intracranial hypertension, and some cases with high intracapsular pressure may produce brain tissue collapse, subdural effusion or even hemorrhage due to excessive shunting. With the continuous improvement of shunt systems and economic development, more and more cases are opting for the application of adjustable valves, which allow for adjustment according to pressure changes, more individualized relief of postoperative discomfort and reduction of complications. However, there are still relatively obvious disadvantages of shunt surgery, most of which require lifelong tubes, which may lead to complications such as shunt dysfunction such as lacunar syndrome, infections, and may require mid-tube changes, with a reported rate of approximately 30% of IAC cases requiring tube changes. Ventriculoscopy (neuroendoscopy): With the continuous development of neuroendoscopic technology in recent years, neuroendoscopic cyst opening has been more and more widely used in the treatment of IAC, which can complete almost all operations of craniotomy in a minimally invasive manner and can eliminate the risk of carrying a tube. However, the procedure requires high requirements for instruments and operations, certain hardware conditions and surgical cooperation, and is difficult to perform, and cannot be carried out in general hospitals. Its complications mainly include subdural effusion and bleeding. My personal experience is that if an arachnoid cyst requires surgery, ventriculoscopy should be the first option, but there are limitations to ventriculoscopy if the child is too young, only a few months old and no more than half a year old. Or if the cyst and hydrocephalus are very severe, or if there is bleeding or inflammation, none of the current conditions are suitable for ventriculoscopy. In addition, if the ventriculoscope cannot communicate with the surrounding ventricular brain pool, it is also not suitable for ventriculoscopy. If ventriculoscopy is not appropriate, then a shunt or craniotomy will be considered. However, it should be pointed out that not all cases are suitable for ventriculoscopic surgery. Nowadays, it is incorrect and lack of medical ethics for some hospitals or some doctors to apply the so-called advanced technology to patients who are not suitable in order to pursue the use of new technology and the innovation of new equipment. Having written so much, I don’t know if the description is clear. All in all, every doctor has the responsibility and obligation to understand the child’s condition clearly and discuss it objectively with the child’s parents, analyze the pros and cons of various treatment modalities, propose the most appropriate treatment plan, and help the parents make the most correct judgment.