Diastematomyelia is a rare congenital neurological disorder classified as an occult spinal dysraphism, a birth defect where the spinal cord or its protective coverings do not form correctly. This condition involves the spinal cord splitting longitudinally into two separate segments, called hemicords. The division is caused by a bony, cartilaginous, or fibrous structure (a septum) that protrudes into the spinal canal. While the extent of the split varies, it most commonly occurs in the lower thoracic and upper lumbar regions of the spine.
Understanding the Spinal Anomaly
The physical characteristic of diastematomyelia is the formation of two distinct spinal cord segments, or hemicords, along a section of the vertebral column. Each hemicord contains its own central canal, dorsal horn, and ventral horn, and the two segments typically rejoin further down the spinal column. This division is caused by a septum that runs through the spinal canal, which can be made of bone, cartilage, or fibrous tissue.
The condition is categorized into two main types based on the anatomy of the dividing structure and the protective dural sac surrounding the spinal cord. Type I diastematomyelia is characterized by a rigid, often bony or osteocartilaginous, spur separating the two hemicords. In this more severe form, each hemicord is encased in its own separate dural sac, effectively creating two spinal canals at the level of the split.
Type II diastematomyelia involves a fibrous or fibrovascular septum dividing the spinal cord, and both hemicords remain contained within a single, continuous dural sac. This type is associated with less severe symptoms compared to Type I. The classification is useful because the nature of the separating structure—rigid bone versus nonrigid fiber—directly influences the mechanical stress placed on the spinal cord and the severity of neurological symptoms.
Causes and Associated Conditions
Diastematomyelia is considered a developmental defect that occurs very early in fetal development, specifically around the third week of gestation. The accepted cause relates to an abnormal adhesion between the embryonic ectoderm and endoderm layers, which results in the notochord developing abnormally. This improper development allows mesodermal tissue, which normally forms bone and cartilage, to invade the developing neural tube, leading to the formation of the separating septum.
While the exact trigger is not fully understood, the condition is frequently associated with other congenital anomalies of the spine and surrounding structures. Patients often have vertebral anomalies such as spina bifida occulta, hemivertebrae, or butterfly vertebrae.
Scoliosis, an abnormal curvature of the spine, is a common co-existing condition and is often identified in over half of affected patients. Another frequent association is tethered cord syndrome, which occurs when the spinal cord becomes abnormally fixed or restricted within the spinal canal. The rigid septum in Type I diastematomyelia often contributes to this tethering by limiting the spinal cord’s normal movement, causing abnormal stretching and progressive neurological issues as the child grows.
Clinical Presentation and Detection
Symptoms are highly variable and may appear from infancy through adulthood, often becoming noticeable during periods of rapid growth that increase tension on a tethered spinal cord. Neurological symptoms frequently involve the lower limbs and perineum, presenting as progressive leg weakness, muscular atrophy, or changes in reflexes. Patients may also develop gait disturbances, foot deformities like clubfoot, or experience chronic low back pain.
Cutaneous stigmata, specific skin markings over the affected spinal area, are present in over half of all cases and can be an important clue for diagnosis. These markings can include a patch of abnormal hair growth (hypertrichosis), skin dimples, hemangiomas, or areas of altered skin pigmentation. Bowel and bladder dysfunction, such as incontinence, can also develop as the spinal cord’s function is progressively impaired.
Diagnosis is confirmed through advanced medical imaging. Magnetic Resonance Imaging (MRI) is the most effective tool, as it provides detailed visualization of the spinal cord structure, the presence of the split, and the nature of the dividing septum. MRI is also essential for detecting associated soft-tissue abnormalities and confirming tethered cord syndrome. X-rays and Computed Tomography (CT) scans are also used, primarily to better evaluate the associated bony anomalies, such as the vertebral defects or an osseous spur.
Treatment and Long-Term Outlook
The primary goal of treatment for diastematomyelia is to prevent progressive neurological deficits, which are caused by the tethering effect of the septum. For patients who are asymptomatic, observation with close neurological monitoring and periodic imaging is often recommended. However, surgical intervention is indicated if a patient presents with new or worsening neurological symptoms.
Surgery involves decompression of the neural elements, including removal of the bony, cartilaginous, or fibrous septum that divides the cord and causes tethering. If tethered cord syndrome is present, the surgeon performs a procedure to release the abnormal attachments, allowing the spinal cord to move freely within the spinal canal.
The long-term prognosis is favorable, especially when the condition is diagnosed and managed surgically before severe neurological damage occurs. While surgery can often stabilize or improve progressive symptoms and relieve pain, it may not reverse neurological deficits or orthopedic deformities that have been present for a long time. Therefore, patients require long-term follow-up with neurological and orthopedic specialists to monitor for any recurrence of symptoms or complications.