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.

Tethered spinal cord can be caused by various conditions but the main cause is when tissue attachments limit the movement of the spinal cord in the spinal column which causes abnormal stretching of the cord. The tethered spinal cord syndrome is correlated with having the causes:

- Spina bifida

- Occulta

- Mylomeningocele

- Meningocele

- History of spinal trauma

- History of spinal surgery

- Tumor(s) in the spinal column

- Thickened and/or tight filum terminale

- Lipoma(s) in the spinal column

- Dermal Sinus Tract (congenital deformity)

- Diastematomyelia (split spinal cord)

Tethered spinal cord is a disorder and not a mechanism so it does not spread to other people and there are no measures that can be done to prevent it beforehand. The only preventative measure that is successful is to surgically untether the spinal cord though there might already be irreversible damage.

In tethered spinal cord cases Spina bifida can be accompanied by tethering of the spinal cord but in rare cases with Spina bifida Occulta. Tethering of the spinal cord tends to occur in the cases of Spina bifida with mylomeningocele. In a normal person the spine grows faster than the spinal cord during development which causes the end of the spinal cord to appear to rise relative to the bony spine next to it. By the time of birth the spinal cord is located between L1 and L2. In a baby with Spina bifida the spinal cord is still attached to the skin around it preventing it from rising properly. This occurs because the spinal cord in a child with Spina bifida is low lying and tethered at the bottom. At the time of birth the mylomeningocele is separated from the skin but the spinal cord is still stuck in the same place. As the child begins to grow the spinal cord remains in the same place becoming stretched out causing the tight cord and the tethering at the end. With this type of tethering there is an interference with the blood supply to the nerves and body which can then cause the deterioration of the body causing orthopedic, neurological, and urological problems. With milder forms of Spina bifida such as Occulta, may be related to the degree of strain on the cord which can become worse with physical activity, injury, pregnancy, bone spurs, or spinal stenosis. The tethered cord in this case might not be diagnosed until adulthood when it worsens and can still cause neurological, orthopedic, and urological dysfunctions.

The signs and symptoms of diastematomyelia may appear at any time of life, although the diagnosis is usually made in childhood. Cutaneous lesions (or stigmata), such as a hairy patch, dimple, Hemangioma, subcutaneous mass, Lipoma or Teratoma override the affected area of the spine is found 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.

Cervical diastematomyelia can become symptomatic as a result of acute trauma, and can cause major neurological deficits, like hemiparesis, to result from otherwise mild trauma.

The following definitions may help to understand some of the related entities:

- Diastematomyelia (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 of anterior and posterior nerve roots.