Syringomyelia

Syringomyelia is a disease in which fluid-filled cavities, referred to as syrinxes, form within the spinal cord. These syrinxes typically persist at high pressure relative to surrounding fluid spaces, which causes progressive neurological symptoms as they expand and elongate over time, compressing the surrounding nerve fibres. The classical clinical sign of a syrinx is a dissociated sensory loss — loss of pain and temperature sensation with preservation of light touch and proprioception. Since the spinal cord connects the brain to nerves in the extremities this damage usually affects the arms and legs. Patients often experience a chronic burning or aching pain, muscles may be stiff and tight or waste away, interfering with movement, profuse sweating is common, blood pressure may be elevated, and lower-limb paralysis may ensue as a late-stage debilitation. Syringomyelia is comparatively rare with 8.4 cases per 100,000, it occurs more frequently in men than in women and usually appears in the third or fourth decade of life, with a mean age of onset of about 30 years. Rarely, syringomyelia may develop in childhood or late adulthood.

About three quarters of all cases occur in combination with an Arnold-Chiari Malformation, an abnormality of the brain, in which the lower part of the cerrebellum protrudes into the upper cervical portion of spinal subarachnoid space, blocking the flow of cerebrospinal fluid (CSF). Severe trauma to the spinal cord often leads to scarring of the surrounding tissues and subsequent syrinx formation, although post-traumatic syringomyelia only accounts for about 10% of all cases.

At present treatment options are limited, with surgical intervention being the most common course of action. The aim is to alleviate the patient's symptoms by reducing the fluid pressure in the spinal cord and in the surrounding subarachnoid space. This is achieved by draining the syrinx, possibly inserting a shunt, and/or removing some of the surrounding bone (either from the vertebrae or the base of the skull, depending on the location of the syrinx).

Although syringomyelia has fascinated neurologists and neurosurgeons for centuries the cause and cure remain elusive. Analysis of clinical cases shows that syringomyelia may be associated with almost any disease of the spinal canal, which has made progress difficult. Poor treatment outcomes have led to myriad hypotheses for its pathogenesis, which unfortunately are often based on small numbers of patients due to the relative rarity of the disease.

Open questions:

• • What is the syrinx fluid source?

  • Is there a CSF pumping mechanism?

  • What causes syrinxes to be so localised?

  • How is syrinx fluid maintained?

  • Do congenital and post-traumatic syringomyelia have the same syrinx filling mechanism?

  • What is the relative importance of cardiovascular (cardiac cycle) and percussive (coughs/sneezes) energy sources?

Mechanically I have approached this problem from several standpoints. I have investigated wave propagation in the spinal canal analytically using asymptotic analysis of 1-d collapsible tube models and numerically by treating the wave dispersion as a harmonic eigenvalue problem. Using a lumped-parameter model I have also investigated the phasic pumping of CSF into the spinal cord.