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DIASTEMATOMYELIA

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 distal to the spur, the condition is referred to as a Diplomyelia (which is a "true duplication" of the Spinal Cord.)

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, hemi-vertebra and "block" vertebrae which are identified in a high proportion of cases. Scoliosis usually affects half of these patients. In most of the symptomatic patients, the Spinal Cord is split into halves by a bony spicule or fibrous band with each half being surrounded by a dural sac. It is exceptionally rare for any other disease states or conditions that may the Spinal Cord to be coincident with Diastematomyelia (such as intramedullary tumors, tethered cord, Dermoids, Lipoma, Syringomyelia, Hydromyelia and Arnold-Chiari malformations).

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. The length of Spinal Cord involved is variable from one patient to another. Involvement of the Cervical levels is a very rare entity.

The two Hemicords, each covered by an intact layer of pia arachnoid, travel through a single subarachnoid space surrounded by a single dural sac in 60% of patients with Diastematomyelia. Each Hemicord has its own blood supply (Anterior Spinal Artery.) This form of Diastematomyelia is usually 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.)

The Conus Medullaris (the "end" of the Spinal Cord which normally is at the T12-L2, levels) is situated below the L2 level in more than 75% of these Diastematomyelia patients. The Filum Terminale is thickened in over half of these patients. While the level of the Diastematomyelia is variable (with most occurring in the Lumbar regions), the two Hemicords usually reunite at some point distal to the "cleft". Occasionally the cleft will extend unusually low and each Cord will end with its own Conus Medullaris and its own Filum Terminale (a condition referred to as "Diplomyelia").

The following definitions may help in the understanding of these 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 or anterior and posterior nerve roots.

SYMPTOMS

At any age, the cause of progressive neurological deficits relates to the fixation of the Spinal Cord ("Tethered Spinal Cord Syndrome") by the Diastematomyelia phenomenon (or any of the associated disorders of the Spinal Cord.) which creates tissue attachments that limit the movement of the Spinal Cord within the Spinal Column. These attachments cause an abnormal stretching of the Spinal Cord.

While the course of the disorder is progressive, the neurological symptoms are nonspecific and usually indistinguishable from other causes of Spinal Cord Tethering. This delayed presentation of symptoms is related to the degree of strain placed on the Spinal Cord over time.

In children, symptoms may include:

  • Foot and spinal deformities
  • Weakness in the legs
  • Low back pain
  • Scoliosis
  • Incontinence
Adult presentation in Diastematomyelia is unusual. The symptoms in adulthood often include:
  • Progressive sensory and motor problems
  • Bowel and bladder incontinence
  • Impotence
  • Onset of pain
  • Autonomic symptoms

DIAGNOSIS

Prenatal ultrasound diagnosis of Diastematomyelia is possible in the early mid third-trimester thus allowing for early surgical intervention and a more favorable prognosis depending on whether the Diastematomyelia is an isolated phenomenon with the skin intact or is in association with more serious neural tube defects.

The signs and symptoms of Diastematomyelia may become manifest at any time in any patient. In current times the diagnosis is more commonly made in childhood. It is common for skin lesions (such as a hairy patch, dimple, Hemangioma, subcutaneous mass, Lipoma or Teratoma) to be present at or near the level of the Diastematomyelia.

Neuroimaging

MRI and CT Scan techniques have dramatically improved the accurate diagnosis of the various types and forms of Spinal Dysraphism. In adults the upper three lumbar vertebrae levels are the most common location for Diastematomyelia whereas Lumbosacral Diastematomyelia is very rare.

MRI scanning is probably the most effective "screening test" for most spinal conditions which includes "Dysraphism". MRI scanning usually provides adequate information about the Spinal Cord and its deformities although it has some significant limitations in giving detailed bone anatomy. Spinal myelography and more specifically post-myelographic CT scan is the most effective diagnostic tool in demonstrating the detailed bone, intradural and extradural pathological anatomy of the affected and adjacent spinal canal levels and of the bony spur.

Figure 1: Post-myelographic CT Scan (Axial View L2,3 level) Diplomyelia

This demonstrates the asymmetrical nature of the duplicated Spinal Cords (the 2 dark "spots" within the Spinal Canal). When there is a bony spicule present, it is usually projects posteriorly from its site of origin in the anterior part of the Spinal Canal (Arrow).


TREATMENT

Surgery

We believe that surgical intervention is warranted in patients who present with new onset neurological signs and symptoms or have a history of progressive neurological manifestations which can be related to this abnormality. The surgical procedure required for the effective treatment of Diastematomyelia requires the decompression of neural elements and removal of bony spur. This may be accomplished with or without resection and repair of the duplicated dural sacs. Our preference is to resect and repair the duplicated dural sacs since the dural abnormality may partly contribute to the "tethering" process responsible for the symptoms of this condition.

Minimally Invasive Microsurgical Techniques are becoming available to accomplish these operative tasks. This most often results in significant relief of symptoms or stops the progression of symptoms. In general, more favorable results are obtained in patients who manifest lesser severity of neurological deficits, have had symptoms and signs for shorter lengths of time and are younger.

Observation

Patients, who are asymptomatic and have been identified with this anomaly while being investigated for other unrelated issues, do not require surgical treatment. These patients should undergo periodic neurological examinations since it is known that the condition can be "progressive". In the event that progressive neurological manifestations are identified, then a resection should then be performed.



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This page last edited on 2/19

All content ©2016 by Neurosurgical Consultants, P.A.
Author, Martin L. Lazar, MD, FACS
All Rights Reserved. See Usage Notices.