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A skull fracture is a break in one or more of the eight bones that form the cranial portion of the skull, usually occurring as a result of blunt force trauma. If the force of the impact is excessive, the bone may fracture at or near the site of the impact and cause damage to the underlying physical structures contained within the skull such as the membranes, blood vessels, and brain, even in the absence of a fracture. While an uncomplicated skull fracture can occur without associated physical or neurological damage and is in itself usually not clinically significant, a fracture in healthy bone indicates that a substantial amount of force has been applied and increases the possibility of associated injury. Any significant blow to the head results in a concussion, with or without loss of consciousness. A fracture in conjunction with an overlying laceration that tears the epidermis and the meninges, or runs through the paranasal sinuses and the middle ear structures, bringing the outside environment into contact with the cranial cavity is called a compound fracture. Compound fractures can either be clean or contaminated. There are four major types of skull fractures: * Linear * Depressed * Diastatic * Basilar Linear fractures are the most common, and usually require no intervention for the fracture itself. Depressed fractures are usually comminuted, with broken portions of bone displaced inward—and may require surgical intervention to repair underlying tissue damage. Diastatic fractures widen the sutures of the skull and usually affect children under three. Basilar fractures are in the bones at the base of the skull. ==Neurocranium== The human skull is anatomically divided into two parts: the neurocranium, formed by eight cranial bones that houses and protect the brain—and the facial skeleton (viscerocranium) composed of fourteen bones, not including the three ossicles of the inner ear.〔Anne M. Gilroy: : Atlas of Anatomy. P.454; Thime Medical Publishers Inc. (2008) ISBN 1-60406-151-0〕 The term ''skull fracture'' typically means fractures to the neurocranium, while fractures of the facial portion of the skull are ''facial fractures'', or if the jaw is fractured, a ''mandibular fracture''.〔Olson RA, Fonseca RJ, Zeitler DL, ''et al.'' Fractures of the mandible: a review of 580 cases. J Oral Maxillofac Surg. 1982 Jan;40(1):23-8. PMID 6950035〕 The eight cranial bones are separated by sutures : one frontal bone, two parietal bones, two temporal bones, one occipital bone, one sphenoid bone, and one ethmoid bone.〔Leon Schlossberg, George D. Zuidema, Johns: The Johns Hopkins Atlas of Human Functional Anatomy, p.5; The Johns Hopkins University Press; (1997) ISBN 0-8018-5652-3〕 The bones of the skull are in three layers: the hard compact layer of the external table (''lamina externa''), the diploë (a spongy layer of red bone marrow in the middle, and the compact layer of the inner table (''Lamina interna'').〔Johannes Lang: Skull base and related structures: atlas of clinical anatomy. P.208. F.K.Schattauer,Germany;(July 1999) ISBN 3-7945-1947-7〕 Skull thickness is variable, depending on location. Thus the traumatic impact required to cause a fracture depends on the impact site. The skull is thick at the glabella, the external occipital protuberance, the mastoid processes, and the external angular process. Areas of the skull that are covered with muscle have no underlying diploë formation between the internal and external lamina, which results in thin bone more susceptible to fractures. Skull fractures occur more easily at the thin squamous temporal and parietal bones, the sphenoid sinus, the foramen magnum (the opening at the base of the skull that the spinal cord passes through), the petrous temporal ridge, and the inner portions of the sphenoid wings at the base of the skull. The middle cranial fossa, a depression at the base of the cranial cavity forms the thinnest part of the skull and is thus the weakest part. This area of the cranial floor is weakened further by the presence of multiple foramina as a result this section is at higher risk for basilar skull fractures to occur. Other areas more susceptible to fractures are the cribriform plate, the roof of orbits in the anterior cranial fossa, and the areas between the mastoid and dural sinuses in the posterior cranial fossa.〔Medscape: Ali Nawaz Khan: Imaging in Skull Fractures ()〕 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「Skull fracture」の詳細全文を読む スポンサード リンク
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