Lateral fissure arachnoid cysts are most commonly found in infants and children and are often detected incidentally during cranial CT examinations after head trauma or when arachnoid cysts lead to increased intracranial pressure and subsequent localized skull bulging. Lateral fissure arachnoid cysts are mostly congenital, occasionally found in fetal life, and after birth, the cysts gradually increase in size, causing the temporal lobe to be compressed and atrophied. After the cyst increases to a certain extent, the cyst may compress the frontal lobe upward and forward; contact the dura mater outward and compress the temporal bone to expand outward; and continue to compress the temporal lobe backward, causing further atrophy of the temporal lobe. Huge arachnoid cysts can gradually lose intracranial pressure buffering mechanism and even cause a slow increase in intracranial pressure. Over time, the compressed brain tissue may form epileptic foci, followed by epilepsy. Lateral fissure arachnoid cysts should be seen in the hospital as soon as they are detected. If the cyst is large and is compressing the brain tissue, or has even caused local skull expansion, it should be treated as early as possible. The most advanced treatment at present is endoscopic cyst-cerebral pool fistulotomy, which involves drilling a hole in the temporal region and cutting open the dirty layer of the cyst endoscopically, so that the cyst is connected to the basal pool and the cyst fluid can enter the basal pool and participate in the cerebrospinal fluid circulation, which in turn causes the cyst pressure to drop and the atrophied brain tissue to gradually recover.