Xu Guangbin, Department of Neurosurgery, Wuhu Second People’s Hospital: Subdural effusion, as the name implies, is the accumulation of fluid under the dura mater inside the skull. It is mostly formed when the cerebral arachnoid is torn by head trauma, causing the cerebrospinal fluid in the subarachnoid space to flow to the subdural area 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 the conditions for the increase of subdural fluid accumulation. The two affect each other and may lead to a slow aggravation of the condition. Subdural effusions are most often seen in the elderly, most often with minor head trauma, or in patients with cerebral atrophy. If the amount of fluid is small, or if brain atrophy is evident in the elderly, it can be observed and neurotrophic agents can be given; if the amount of fluid is large, CT shows signs of intracranial occupancy or displacement of midline structures, or combined with bleeding, surgery is required. We usually use cone-hole drainage, which is a minimally invasive procedure. Under local anesthesia, a small incision of half a centimeter is made on the scalp and a small hole is coned in the skull, and a soft silicone tube is placed to drain the fluid for 2-3 days.