Diastematomyelia

What is Diastematomyelia?

Diastematomyelia can be defined as a congenital disorder, in which a part of the spinal cord is divided. The most common area in which such changes are encountered is the one around the upper lumbar vertebra. This is rare anomaly, with the spinal cord being divided on the longitudinal or sagittal direction. Diastematomyelia is more often encountered in men than in women. The most common association of this condition is with spina bifida. The condition is more often diagnosed in childhood, even though it can become obvious in the latter stages of life as well. It is also known as the split cord malformation and a type of spinal dysraphism (spina bifida occulta).The complete or partial division of the spinal cord is due to the presence of a septum in the central part of the spinal canal. This septum can be formed out of bone tissue or it can be cartilaginous or fibrous. However, regardless of the tissue from which it is formed, it is clear that it leads to the splitting of the spinal cord into two distinct hemicords. In the situation that there is no reuniting of the split, this condition is known as diplomyelia (this meaning that the entire spinal cord is divided). Almost 4% of all the congenital spinal defects include patients diagnosed with this condition.

Pathophysiology

Radiographic Picture of Diastematomyelia

The exact embryonic origin of diastematomyelia is not known but scientists believe that this condition is caused by the presence of an additional embryonic spinal canal. Other have suggested that the neural tube fails to organize and differentiate from the primitive neuroectoderm in the first part of the pregnancy. This leads to the persistence of abnormal mesodermal cells at the level of the neural tube.It is possible that this condition appears on its own (isolated) or in conjunction with other anomalies involving the spine, such as block vertebrae, hemivertebra, butterfly vertebra, spina bifida or kyphoscoliosis. In fact, more than half of the patients who present this condition also have scoliosis.The septum that divides the spinal cord is generally constituted out of osseous or fibrous tissue, with each half of the spinal cord being protected by its own dural sac (valid for symptomatic patients). In the majority of the patients, the division is found between the 9th thoracic and 1st sacral vertebrae, with the most common being at the level of the upper lumbar vertebrae. There are only a few cases of cervical division. The length of the affectation (how much of the spinal cord is involved) varies from one person to the other.There is a form of diastematomyelia that do not cause any symptoms, unless it is found in association with other changes, such as hydromyelia or tethering. In this form, each of the hemicords is covered by an individual layer of pia arachnoid. However, they travel through the same subarachnoid space, being surrounded by the same dural sac. In regard to the vascularization, you should keep in mind that each of the hemicords has its own anterior spinal artery. No bony spurs or fibrous bands have been encountered in this form of diastematomyelia (60% of the patients).For the other form of diastematomyelia, the spinal cord is split by a bone spur or a fibrous band (40% of the patients). The splitting is encountered at the level of the dura and the arachnoid as well, each having its own individual sac. Each of the hemicords will present a central canal, as well as two horns (ventral and dorsal). The ventral horn will give rise to the ventral nerve root, while the dorsal horn will give rise to the dorsal nerve root.

Types of Diastematomyelia

From what has been said so far, you have probably understood that there are two main types of diastematomyelia:

Type 1

• This is the type with the duplicated dural sac, in which the spinal cord is divided by an osseous or fibrous midline spur (most commonly, these patients are symptomatic)
• Classic form
• Hydromyelia is also present
• Associated vertebral anomalies
• Skin pigmentation
• Associated with the tethered cord syndrome

Type 2

• This is the type in which a single dural sac is present, containing both of the hemicords (the impairment is less marked)
• Milder than the 1st type
• No bone or fibrous spur present
• Hydromyelia can also be present
• Spina bifida may be the only associated vertebral anomaly (others are extremely rare)
• The majority of the patients is asymptomatic (symptoms are rarely present and of decreased intensity)

One of the most common areas in which the bone spur is located is the dural cleft (most inferior aspect of). It is also possible that more than one bone spur or fibrous band is encountered at the level of the spinal cord. The hemicords reunite in an inferior area to the dural cleft. If the dural cleft is located very low, it is possible that each hemicords continues on its own, without uniting (diplomyelia).Among the associated anomalies that are found in these patients, there are: meningocele, neurenteric cyst, dermoid, club foot, spinal cord lipoma and hemangioma overlying the spine.

Signs and Symptoms

These are the most common signs and symptoms that are suggestive of diastematomyelia:

• Cutaneous lesions (stigmata) – these are found in the area where the spine is affected (50% of the patients)
• Hairy patch
• Dimple
• Hemangioma
• Subcutaneous mass
• Lipoma/teratoma
• Neurological symptoms
• Non-specific
• Can be difficult to be distinguished from other health problems that lead to the tethering of the spinal cord
• In children (progressive symptoms):
• Foot and spinal deformities
• Leg weakness
• Low back pain
• Scoliosis
• Incontinence
• In adults:
• Progressive sensory and motor problems
• Loss of bowel and bladder control
• Other symptoms
• Gait disorder
• Muscular atrophy
• Reflex changes (absent deep tendon reflexes)
• Progressive paraparesis.

In the situation that a person suffers from progressive neurological impairment, involving the lower extremities and also leading to the bladder/bowel dysfunction, it is apparent that such changes result from the increasing distortion of the neural axis. This distortion is caused by the fixation of the bone or fibrous spurs, occurring during the actual growth period.

Diagnosis

These are the most common methods used for the diagnosis of diastematomyelia:

Imaging techniques

• Often used for the confirmation of the diagnosis
• Most common location of the lesion – 1st-3rd lumbar vertebrae
• Plain X-ray (anteroposterior and lateral spine films)
• Identify bone malformations or dysplasias
• The identification of multi-level spina bifida
• The interpedicular distance will appear widened
• Associated scoliosis
• The vertebral bodies are narrowed (anteroposterior)
• MRI
• First choice of screening and diagnosis, especially in children
• Adequate analysis of the deformities that exist at the level of the spinal cord
• Can be used to attest the presence of hydromyelia
• Limitations – detailed bone anatomy
• CT scan (myelography and post-myelographic)
• Effective diagnostic tool – detailed bone analysis
• Can also be used to assess the spinal canal and the bony spur (intradural and extradural pathological anatomy)
• Reveals the two different anterior spinal arteries for each of the hemicords

Prenatal ultrasound

• Potential diagnosis of diastematomyelia – early to mid-3rd trimester
• Allows for early surgical intervention (better prognosis)
• Can also be used to identify whether the fetus presents other anomalies or neural tube defects.

It should be noted that, in children, the imaging studies are essential for the confirmation of the diagnosis. This is because the neurological signs, as well as the other symptoms presented, are not specific for diastematomyelia.

Treatment

These are the most common methods used for the treatment of diastematomyelia:

• Surgical intervention
• Recommended in patients who present an acute onset of neurological signs and symptoms
• Also indicated in those who have a history of progressive neurological manifestations
• Decompression surgery – purpose of the surgery is to relieve the neural elements of the pressure, by removing the bone spur or fibrous band
• May require the resection, followed by the necessary repair, of the duplicated dural sacs
• The last action is required so as to eliminate the symptoms caused by the tethering syndrome
• Can also be used prophylactically – reduce the chance for neurological symptoms in patients who are asymptomatic; indicated in symptomatic patients as well, so as to prevent the clinical deterioration
• Scoliosis surgery
• Recommended only after the bone or fibrous spur has been removed

It should be mentioned that no treatment is required in patients who are asymptomatic. On the other hand, they should visit the doctor on a regular basis – the neurological check-ups can determine whether this condition has deteriorated or not. In the situation that the condition leads to the appearance of progressive symptoms, the surgical intervention is going to be considered.In the situation that the diagnosis is made during infancy or early childhood, it is recommended that the surgical intervention is performed close to that time. This will guarantee the best outcome and long-term prognosis for the patient diagnosed with diastematomyelia.