Our studies demonstrate a mechanism of the pathogenesis of syringomyelia in which (1) the Chiari malformation partially obstructs the cerebrospinal fluid (CSF) pathways at the foramen magnum; (2) the normally rapid efflux and influx of CSF between the head and the spine, which normally compensates for brain expansion and contraction during the cardiac cycle, is blocked; (3) the cerebellar tonsils are displaced during the cardiac cycle, in lieu of CSF, creating a piston effect on the partially entrapped spinal subarachnoid space; (4) enlarged cervical subarachnoid pressure waves are created, which compress the spinal cord from without, direct CSF into the spinal cord, and cause pulsatile syrinx flow; which in turn (5) leads to syrinx progression. These findings are consistent with an origin of the syrinx fluid by pulsatile-facilitated transmission of CSF through the spinal cord. This mechanism of syrinx origin, progression, and resolution arises outside, not inside, the spinal cord. Thus, extraarachnoidal craniocervical decompression and duroplasty reverses the mechanism of syringomyelia progression without invading the central nervous system parenchyma or the CSF pathways and consistently provides a safe and effective treatment of patients with Chiari I and syringomyelia.
