Editing Subdural hematoma (section)

===Classification===
Subdural hematomas are classified as [[Acute (medicine)|acute]], subacute, or [[chronic (medicine)|chronic]], depending on the speed of their onset.<ref>{{EMedicine|article|247472|Subdural Hematoma Surgery}}</ref>

Acute bleeds often develop after high-speed acceleration or deceleration injuries. They are most severe if associated with [[cerebral contusion]]s.<ref name="wagner" /> Though much faster than chronic subdural bleeds, acute subdural bleeding is usually venous and therefore slower than the arterial bleeding of an epidural hemorrhage. Acute subdural hematomas due to trauma are the most lethal of all head injuries and have a high [[mortality rate]] if they are not rapidly treated with surgical decompression.<ref>{{Cite web |last=<!--Staff writer(s); no by-line.--> |title=Acute Subdural Hematomas |url=http://neurosurgery.ucla.edu/body.cfm?id=102 |access-date=21 July 2011 |website=UCLA Health}}</ref> The mortality rate is higher than that of epidural hematomas and [[Focal and diffuse brain injury|diffuse brain injuries]] because the force required to cause subdural hematomas tends to cause other severe injuries as well.<ref>{{EMedicine|article|247664|Penetrating Head Trauma}}</ref>

Chronic subdural bleeds develop over a period of days to weeks, often after minor head trauma, though a cause is not identifiable in 50% of patients.<ref name="Downie">Downie A. 2001. [http://www.radiology.co.uk/srs-x/tutors/cttrauma/tutor.htm "Tutorial: CT in head trauma"] {{Webarchive|url=https://web.archive.org/web/20051106231525/http://www.radiology.co.uk/srs-x/tutors/cttrauma/tutor.htm |date=2005-11-06 }}. Retrieved on August 7, 2007.</ref> They may not be discovered until they present clinically months or years after a head injury.<ref name="Kushner98">{{Cite journal |vauthors=Kushner D |year=1998 |title=Mild traumatic brain injury: toward understanding manifestations and treatment |journal=Archives of Internal Medicine |volume=158 |issue=15 |pages=1617–1624 |doi=10.1001/archinte.158.15.1617 |pmid=9701095 |doi-access=free}}</ref> The bleeding from a chronic hematoma is slow and usually stops by itself.<ref name="UVT" /><ref>{{Cite journal |vauthors=Faried A, Halim D, Widjaya IA, Badri RF, Sulaiman SF, Arifin MZ |date=October 2019 |title=Correlation between the skull base fracture and the incidence of intracranial hemorrhage in patients with traumatic brain injury |journal=Chinese Journal of Traumatology = Zhonghua Chuang Shang Za Zhi |volume=22 |issue=5 |pages=286–289 |doi=10.1016/j.cjtee.2019.05.006 |pmc=6823676 |pmid=31521457}}</ref> Because these hematomas progress slowly, they can more often be stopped before they cause significant damage, especially if they are less than a centimeter wide. In one study, only 22% of patients with chronic subdural bleeds had outcomes worse than "good" or "complete recovery".<ref name="wagner" /> Chronic subdural hematomas are common in the elderly.<ref name="Kushner98" />