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Diastomatomyelia is a congenital disorder in which a part of the spinal cord is split, usually at the level of the upper lumbar vertebra.
Diastomatomyelia 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 distal to the spur, the condition is referred to as a Diplomyelia (which is a “true duplication” of the Spinal Cord.)
Diastomatomyelia 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 a high proportion of cases. Scoliosis is usually 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 the medical literature, but are exceptionally rare.
Diastomatomyelia 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 Diastomatomyelia 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 Diastomatomyelia, 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 Diastomatomyelia is not accompanied by a 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 of these entities identified the bony spur as typically being situated at the most inferior aspect of the dural cleft. They advise that if the imaging study appears to show otherwise, a second spur (present in about 5% of patients with Diastomatomyelia) is likely to be present.
The conus medullaris is situated below the L2 level in more than 75% of these Diastomatomyelia patients. Thickening of the Filum Terminale is seen in over half of them. While the level of the cleft is variable, it is most commonly found in the lumbar region. The two hemicords usually reunite caudal 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 (sometimes called “Diplomyelia”).
The following definitions from may help in the understanding of these entities:
Diastomatomyelia (di·a·stem·a·to·my·elia) is a congenital anomaly, often associated with spina bifida, in which the spinal cord is split into halves by a bony spicule or fibrous band, each half being surrounded by a dural sac.
Myeloschisis (my·elos·chi·sis) is a developmental anomaly characterized by a cleft spinal cord, owing to failure of the neural plate to form a complete neural tube or to rupture of the neural tube after closure.
Diplomyelia (diplo.my.elia) is a true duplication of spinal cord in which these are two dural sacs with two pairs or anterior and posterior nerve roots.
DIAGNOSIS The signs and symptoms of Diastomatomyelia may appear at any time of life, although the diagnosis, in modern times, is usually made in childhood. Cutaneous lesions (or stigmata), such as a hairy patch, dimple, Hemangioma, subcutaneous mass, Lipoma or Teratoma (at or near the level of the Diastomatomyelia) override the affected area of spine in more than half of cases. Neurological symptoms are nonspecific, indistinguishable from other causes of cord tethering. The symptoms are caused by tissue attachments that limit the movement of the spinal cord within the spinal column. These attachments cause an abnormal stretching of the spinal cord. The course of the disorder is progressive. In children, symptoms may include the “stigmata” mentioned above and/or foot and spinal deformities; weakness in the legs; low back pain; scoliosis; and incontinence. In adulthood, the signs and symptoms often include progressive sensory and motor problems and loss of bowel and bladder control. This delayed presentation of symptoms is related to the degree of strain placed on the spinal cord over time. Tethered spinal cord syndrome appears to be the result of improper growth of the neural tube during fetal development, and is closely linked to spina bifida. Tethering may also develop after spinal cord injury and scar tissue can block the flow of fluids around the spinal cord. Fluid pressure may cause cysts to form in the spinal cord, a condition called syringomyelia. This can lead to additional loss of movement, feeling or the onset of pain or autonomic symptoms.
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