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Epidural or extradural hematoma (haematoma), also known as an epidural hemorrhage, is a type of traumatic brain injury (TBI) in which a buildup of blood occurs between the dura mater (the tough outer membrane of the central nervous system) and the skull. The spinal cord is also covered by a layer of dura mater, so epidural bleeds may also occur in the spinal column. Often due to trauma, the condition is potentially deadly because the buildup of blood may increase pressure in the intracranial space, compress delicate brain tissue, and cause brain shift. The condition is present in one to three percent of head injuries. Around 15% - 20% of epidural hematomas are fatal.〔Sanders MJ and McKenna K. 2001. ''Mosby’s Paramedic Textbook'', 2nd revised Ed. Chapter 22, "Head and Facial Trauma." Mosby.〕 ==Signs and symptoms== Epidural, subdural, and subarachnoid hemorrhages are extra-axial bleeds, occurring outside of the brain tissue, while intra-axial hemorrhages, including intraparenchymal and intraventricular hemorrhages, occur within it. Epidural hematomas may present with a lucid period immediately following the trauma and a delay before symptoms become evident. After the epidural hematoma begins collecting, it starts to compress intracranial structures which may impinge on the CN III.〔 This can be seen in the physical exam as a fixed and dilated pupil on the side of the injury.〔(Epidural Hematoma in Emergency Medicine ) at Medscape. Author: Daniel D Price. Updated: Nov 3, 2010〕 The eye will be positioned down and out, due to unopposed CN IV and CN VI innervation. Other manifestations will include weakness of the extremities on the opposite side as the lesion (except in rare cases), due to compression of the crossed pyramid pathways, and a loss of visual field opposite to the side of the lesion, due to compression of the posterior cerebral artery on the side of the lesion. The most feared event that takes place is the transtentorial, or uncal herniation which results in respiratory arrest since the medullary structures are compromised. The trigeminal nerve (CN V) may be involved late in the process as the pons becomes compressed, but this is not a significant clinical presentation, since by that time the patient may already be dead.〔Wagner AL. 2006. ("Subdural Hematoma." ) Emedicine.com. Retrieved on February 6, 2007.〕 In the case of epidural hematoma in the posterior cranial fossa, the herniation is tonsillar and causes the Cushing's triad: hypertension, bradycardia, and irregular respiration. Epidural bleeding is rapid because it is usually from arteries, which are high pressure. Epidural bleeds from arteries can grow until they reach their peak size at six to eight hours post injury, spilling from 25 to 75 cubic centimeters of blood into the intracranial space.〔 As the hematoma expands, it strips the dura from the inside of the skull, causing an intense headache. Epidural bleeds can become large and raise intracranial pressure, causing the brain to shift, lose blood supply, or be crushed against the skull. Larger hematomas cause more damage. Epidural bleeds can quickly expand and compress the brain stem, causing unconsciousness, abnormal posturing, and abnormal pupil responses to light.〔Singh J and Stock A. 2006. ("Head Trauma." ) Emedicine.com. Retrieved on February 6, 2007.〕 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「Epidural hematoma」の詳細全文を読む スポンサード リンク
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