The spinal cord is divided vertically into two hemicords by a fibrous, bony or osteocartilagenous septum in diastematomyelia. Each hemicord has its own central canal and pia surrounding it. The cord is usually split locally, with a single cord above and below the cleft as in this case. The cleft is located between T9 and S1 in 85% of cases.There are two types of diastematomyelia. Type I consists of two hemicords, each contained within its owndural tube and separated by a dura-sheathed rigid osseocartilaginousmedian septum. Type II diastematomyelia consists of two hemicords contained in a single dural tube with the hemicords separated by a nonrigid fibrous median septum. Females are affected more commonly (80%) than males. In two-thirds of cases the overlying skin shows naevi, hypertrichosis, lipomas or dimples. Symptoms are nonspecific and similar to other causes of cord tethering.
This disorder may result from splitting of the notochord around an adhesion between the endoderm and the ectoderm. This split notochord might influence the formation of two neural tubes and subsequently two hemicords. The notochord also influences the vertebrae formation and thus it is common to have associated segmentation anomalies at the site of diastematomyelia.
These patients have sphincteric disturbances and neurological deficits in the lower limbs, such as gait disturbances, muscular atrophy, reflex changes, and foot deformities, which do not manifest themselves until walking begins.
Diastematomyelia and diplomyelia are different anomalies. The former consists of two hemicords and is often associated with spina bifida. It’s longitudinal splitting of spinal cord at one or more levels. The latter is the true duplication spinal cord and consists of two dural sacs, two pairs of anterior and posterior nerve roots.
Anomalies found in association with diastematomyelia are vertebral body anomalies (hemivertebrae, block or butterfly vertebrae and narrow intervertebral disks), congenital scoliosis, spina bifida, thickened filum terminale and tethered cord.
Tethered cord syndrome is characterised by an abnormally short and thickened filum terminale and low position of the conus medullaris. The primary causes of tethered spinal cords include the following conditions: dermal sinus tract, diastematomyelia (split spinal cord), lipoma, tumour, myelomeningocele ("spina bifida"), and tight filum terminale. Other causes can include past trauma or surgery on the spine. The spinal cord is fixed between two points: first at the tethering structure and second at the base of the brain. Thus, vertebral structures that move as a result of growth, daily activity, or pathological skeletal change (scoliosis or curvature of the spine) will stretch the spinal cord abnormally. The result is that this segment of tethered spinal cord is stretched beyond its tolerance and damage to blood vessels, nerve cells, and nerve fibres occurs. The most common findings or complaints include decrease in strength of the legs, loss of bowel and bladder control, deformity of the legs or hips, back or leg pain, loss of reflexes and sensation in the legs, and curvature of the spine. Often there are skin abnomalities overlying the tethered cord such as midline dimples, sinuses or tracts leading from the skin toward the spinal cord, birthmarks, fatty lumps, or small tufts of hair. All tethered cord patients need surgery to prevent further neurological losses. Surgery consists of gently releasing the spinal cord from the tissue that it is stuck to.
