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Diastematomyelia (occasionally diastomyelia) is a congenital disorder in which a part of the spinal cord is split, usually at the level of the upper lumbar vertebra. Diastematomyelia is a rare congenital anomaly that results in the "splitting" of the spinal cord in a longitudinal (sagittal) direction. Females are affected much more commonly than males. This condition occurs in the presence of an osseous (bone), cartilaginous or fibrous septum in the central portion of the spinal canal which then produces a complete or incomplete sagittal division of the spinal cord into two hemicords. When the split does not reunite distally to the spur, the condition is referred to as a diplomyelia, or true duplication of the spinal cord. ==Pathophysiology== Diastematomyelia is a "dysraphic state" of unknown embryonic origin, but is probably initiated by an accessory neurenteric canal (an additional embryonic spinal canal.) This condition may be an isolated phenomenon or may be associated with other segmental anomalies of the vertebral bodies such as spina bifida, kyphoscoliosis, butterfly vertebra, hemivertebra and block vertebrae which are observed in most of the cases. Scoliosis is identified in more than half of these patients. In most of the symptomatic patients, the spinal cord is split into halves by a bony spicule or fibrous band, each half being surrounded by a dural sac. Other conditions, such as intramedullary tumors, tethered cord, dermoids, lipoma, syringomyelia, hydromyelia and Arnold-Chiari malformations have been described in medical literature, but they are exceptionally rare. Diastematomyelia usually occurs between 9th thoracic and 1st sacral levels of the spinal column with most being at the level of the upper lumbar vertebra. Cervical diastematomyelia is a very rare entity. The extent (or length of spinal cord involved) varies from one affected individual to another. In approximately 60% of patients with diastematomyelia, the two hemicords, each covered by an intact layer of pia arachnoid, travel through a single subarachnoid space surrounded by a single dural sac. Each hemicord has its own anterior spinal artery. This form of diastematomyelia is not accompanied by any bony spur or fibrous band and is rarely symptomatic unless hydromyelia or tethering is present. The other 40% of patients have a bony spur or a fibrous band that passes through the two hemicords. In these cases, the dura and arachnoid are split into two separate dural and arachnoidal sacs, each surrounding the corresponding hemicord which are not necessarily symmetric. Each hemicord contains a central canal, one dorsal horn (giving rise to a dorsal nerve root), and one ventral horn (giving rise to a ventral nerve root.) One study showed the bony spur typically situated at the most inferior aspect of the dural cleft. They advised that if the imaging appears to show otherwise, a second spur (present in about 5% of patients with diastematomyelia) is likely to be present. The conus medullaris is situated below the L2 level in more than 75% of these diastematomyelia patients. Thickening of the filum terminale is seen in over half of the cases. While the level of the cleft is variable, it is most commonly found in the lumbar region. The two hemicords usually reunite caudally to the cleft. Occasionally, however, the cleft will extend unusually low and the cord will end with two separate coni medullarae and two fila terminale ("Diplomyelia"). 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「Diastematomyelia」の詳細全文を読む スポンサード リンク
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