A subdural effusion is, as the name implies, an accumulation of fluid under the dura mater inside the skull. It is usually formed when the cerebral arachnoid is torn by head trauma, causing cerebrospinal fluid from the subarachnoid space to flow into the subdural space outside the arachnoid. Since the cerebrospinal fluid in the subarachnoid space can be absorbed into the bloodstream, while the subdural fluid is not easily absorbed, it may accumulate more and more, further causing brain atrophy, which provides conditions for the increase of subdural fluid accumulation. The two affect each other and may lead to a slow aggravation of the condition. The cerebrospinal fluid accumulates under the dura mater to form subdural fluid, which tends to occur in the frontal, temporal and parietal areas. Rupture of the arachnoid membrane due to cranial trauma is the main cause of effusion, and the older and more severely injured the patient, the more likely it is to occur. In acute cases, the fluid can form within a few hours after the injury, and most of them have clinical symptoms and are not easily missed. Chronic effusion is also known as subdural hydrocele, and the effusion is often wrapped by membranes and appears as a crescent-shaped hypointense shadow on CT films. Chronic subdural effusions can occur days or weeks after trauma and are often missed or misdiagnosed due to the lack of obvious clinical symptoms. Chronic subdural effusions are most often seen in the elderly and the history of trauma is often overlooked by patients. This is because there are varying degrees of brain atrophy in the elderly, with sufficient voids in the cranial cavity to cushion the increased pressure of cerebrospinal fluid spillage, and patients are asymptomatic. Most patients are reminded by their physicians before they recall a history of falls or bumps that have touched their heads. If there are no clinical symptoms of increased intracranial pressure, the subdural fluid does not need to be treated and will slowly absorb. Cranial CT can also be reviewed to dynamically observe whether the amount of fluid accumulation increases. Of course, if the cerebrospinal fluid overflows too much, and the patient has a feeling of head rising, headache, or even manifestations such as convulsions or weakness of limbs, it needs to be treated. Therefore, you can visit the neurosurgery department of your local hospital, and the doctor will provide advice on whether further consultation and treatment are needed according to your specific situation. The key to the treatment of subdural fluid in infants and children is to remove the fluid in a timely manner, promote the absorption of the residual fluid and prevent the re-formation of the fluid. With the popularization of CT, the diagnosis of subdural effusion in infants and children is easier and the morbidity and mortality rate is much lower than before, but the correct treatment measures still need to be taken as early as possible to improve the quality of survival of the child. The use of a 9-gauge scalp needle to puncture and drain the outer corner of fontanelle is effective, easy to perform, and does not require extraordinary instruments, and can be performed in the operating room, disposal room, or ward. Patients with poor results of repeated puncture and drainage should undergo surgery as soon as possible to facilitate the recovery of brain function in children. For refractory cases, we use subdural-abdominal shunt and tipped large omental subdural graft. Because the large omentum can both absorb the fluid and increase the blood circulation of brain tissue, while subdural-peritoneal shunt can drain the fluid for a long time, lower the intracranial pressure and provide sufficient time and conditions for brain expansion to facilitate the recovery of brain atrophy. Those with high protein content of subdural fluid are not suitable for shunt surgery.