Today I’m here to talk about arachnoid cysts. I often encounter very anxious parents in the clinic who bring their children in: Doctor Doctor, I found something in my child’s brain! On closer reading of the film, it turns out to be an arachnoid cyst. The incidence of arachnoid cysts in the population is not low, about 0.1 to 0.7%. They are more common in children because about 75% of arachnoid cysts are detected in childhood. And the incidence is higher in boys than in girls. Most arachnoid cysts are asymptomatic and are only occasionally detected during an examination after head trauma. So most of those who come to see arachnoid cysts are naughty boys, and despite the anxiety of their parents, the children appear to be healthy. Chen Ruoping of the Department of Neurosurgery at Shanghai Children’s Hospital currently believes that most arachnoid cysts form during fetal development. However, there are a few cysts associated with head trauma during infancy. We do not know much about the natural course of arachnoid cysts: most arachnoid cysts can remain in a static state for a long time, neither growing nor shrinking; a few can grow progressively and compress brain tissue to produce symptoms; very few can shrink or even subside spontaneously. The most common site for arachnoid cysts is in the temporal lobe, which accounts for about half of them. However, in children, significantly more cysts are located in the saddle area and cerebellar region than in adults. We will talk about the symptoms of arachnoid cysts located in the temporal region. As mentioned earlier, most arachnoid cysts are asymptomatic and do not affect the child’s motor or intellectual development, so these children are generally bright and cute. However, careful observation may reveal that some children have a bulge on one side of the temporal bone. Generally speaking, the higher the bulge, the larger the cyst and the greater the local pressure on the cyst. The typical symptom of temporal arachnoid cyst is a unilateral headache on the side of the cyst, most typically in the temporal or orbital region. However, because the headache is not very severe, it is rarely described in younger children, and more definite descriptions of such headaches are usually found in children 8 to 9 years of age. Seizures can occur in approximately 25% of temporal arachnoid cysts and may be related to localized brain tissue compression. It should be noted that arachnoid cysts can rupture in the setting of minor trauma, followed by acute or chronic intracranial hemorrhage. Huge cysts in infants and children can also lead to significant enlargement of the skull. The most important treatment concern is discussed below. The treatment of arachnoid cysts is still controversial, especially whether they need to be treated and which method of treatment to adopt. One scholar, Galassi, divides temporal arachnoid cysts into three types: I, II, and III. Type I and asymptomatic II cysts do not require treatment and can be reviewed once or twice a year with a cranial MRI. Monitoring of head circumference is also required for infants and children. If the child remains asymptomatic, the cyst does not change on review, and the child’s head circumference does not progressively increase, follow-up reviews will continue. Surgery may be considered for symptomatic type II (marked localized temporal bone elevation, headache, seizures, and progressive increase in head circumference) and type III cysts. It is important to note that arachnoid cysts are benign lesions that have a fairly slow course and are generally not life threatening to the child unless they rupture. There are currently three surgical options for arachnoid cysts: cyst abdominal bypass, cyst excision with fistula, and neuroendoscopic cyst excision with fistula. Cystoperitoneal shunt is the most effective surgical approach, which is simple and minimally invasive, and in most cases is the most commonly used surgical procedure for arachnoid cysts. However, the disadvantage is that it requires the implantation of a shunt, which can often produce multiple adverse comorbidities, blockages, infections, etc. over a considerable period of time. If an inappropriate shunt is chosen, it can also lead to cerebellar ventricular syndrome. The advantage of cystectomy with fistula, either by microsurgery or neuroendoscopic surgery, is that the procedure is effective, does not require the use of a shunt, and can avoid all the problems associated with shunts. However, the disadvantages are that these two procedures are more complicated and relatively more traumatic, and the possibility of accidents during surgery is also high. Moreover, if the operation fails, a cystic abdominal shunt is still needed. Our department uses all 3 surgical procedures, but prefers to use cystectomy with fistula. Especially, we are not only good at neuroendoscopic surgery, but also at locked-hole surgery. Compared to the traditional open flap microsurgery, the locked foramen has the advantages of less surgical trauma and faster recovery after surgery. We hope that you can truly understand arachnoid cysts. Thank you for reading.