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A subdural hematoma (American spelling) or subdural haematoma (British spelling), also known as a subdural haemorrhage (SDH), is a type of hematoma, usually associated with traumatic brain injury. Blood gathers between the dura mater, and the brain. Usually resulting from tears in bridging veins which cross the subdural space, subdural hemorrhages may cause an increase in intracranial pressure (ICP), which can cause compression of and damage to delicate brain tissue. Subdural hematomas are often life-threatening when acute. Chronic subdural hematomas, however, have a better prognosis if properly managed. In contrast, epidural hematomas are usually caused by tears in arteries, resulting in a build-up of blood between the dura mater and skull. ==Classification== Subdural hematomas are divided into acute, subacute, and chronic, depending on the speed of their onset. Acute subdural hematomas that are 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.〔UCLA Neurosurgery () retrieved on 7/21/2011.〕 Acute bleeds often develop after high speed acceleration or deceleration injuries and are increasingly severe with larger hematomas. They are most severe if associated with cerebral contusions.〔 Though much faster than chronic subdural bleeds, acute subdural bleeding is usually venous and therefore slower than the typically arterial bleeding of an epidural hemorrhage. Acute subdural bleeds have a high mortality rate, higher even than epidural hematomas and diffuse brain injuries, because the force (acceleration/deceleration) required to cause them causes other severe injuries as well. The mortality rate associated with acute subdural hematoma is around 60 to 80%. Chronic subdural bleeds develop over a period of days to weeks, often after minor head trauma, though such a cause is not identifiable in 50% of patients.〔Downie A. 2001. ("Tutorial: CT in head trauma" ). Retrieved on August 7, 2007.〕 They may not be discovered until they present clinically months or years after a head injury.〔 〕 The bleeding from a chronic bleed is slow, probably from repeated minor bleeds, and usually stops by itself.〔〔Graham DI and Gennareli TA. Chapter 5, "Pathology of brain damage after head injury" Cooper P and Golfinos G. 2000. ''Head Injury'', 4th Ed. Morgan Hill, New York.〕 Since these bleeds progress slowly, they present the chance of being stopped before they cause significant damage. Small chronic subdural hematomas, those less than a centimeter wide, have much better outcomes than acute subdural bleeds: in one study, only 22% of patients with chronic subdural bleeds had outcomes worse than "good" or "complete recovery".〔 Chronic subdural hematomas are common in the elderly.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Subdural hematoma」の詳細全文を読む スポンサード リンク
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