Tethered cord is when the spinal cord is too short for the spine it is attached to.
For the most part the brain floats inside the cranial vault. The spinal cord is likewise unattached inside the spinal canal. Its only point of attachment is at the tail end of the cord, called the filum terminale. Its attached to the tailbone of the spine, known as the coccyx. Because of this attachment, the cord tractions the brainstem inside the skull and the lumbosacral plexus of nerves in the low back and pelvis.
This syndrome occurs in children and young adults for various reasons most likely due to inherited (genetic) design problems and disorders. The pictures below show the spinal cord to the left and it’s attachment at the base of the spine on the right.
Sometimes the length of the cord is too short. Sometimes the body grows too fast for the cord. The cord stops growing around age eleven, therefore, tethered cord may also play a role in scoliosis. As the cord stops growing it stresses and strains the spine as it continues to lengthen, thereby creating abnormal curvatures called scoliosis.
Scoliosis is typically benign but in certain cases it can cause profound changes in physiology. As for the spinal cord, scoliosis causes functional stenosis, which means narrowing of the spinal canal. That is, the cord pulls tight against the inside curve of the spinal canal which mimics the shape of the spine. The postion of the cord compresses the veins that lie between the cord and spinal canal disturbing blood flow.
In addition to blood flow, curvatures of the spine also affect cerebrospinal fluid flow (CSF) in the subarachnoid space of the cord. Interestingly, certain cases of curvature problems in the spine are associated with lesions in the cord that show up as hyperintensity signals on MRI.
The tension in the lower end of the cord can also irritate the nerves in the lower part of the nervous system. In particular, it can irritate and affect the function of the organs of the pelvis, which include the reproductive organs, bladder and bowel. Reproductive signs can be subtle. On the other hand, key signs of bowel and bladder problems are frequency, urgency and loss of control.
In addition to scoliosis and pelvic problems tethered cord syndromes can cause a Chiari malformation. A Chiari malformation occurs when the brainstem and cerebellum gets pulled down toward, or into the foramen magnum. Chiari malformations can cause compression of the brain and brainstem.