Spinal cord swelling preceding syrinx development

explain the pathophysiology of syringomyelia associated with the Chiari I malformation. In some of them, mechanisms in which the syrinx expands progressively from an initially small locus of syringomyelia, a “drop” of fluid, to a cavity that is large enough to distend the spinal cord are proposed. This is the mechanism proposed for the theories advocated by Gardner and Angel,4,5 and Williams18–20 in which the persistence of a communication between the fourth ventricle and the central canal at the obex is required, as it is in the suggestion of Milhorat and colleagues13–15 that the syrinx results from an obstruction of the central canal by ependymal hyperplasia occluding rostral flow of CSF in the central canal. If these theories are correct, hydromyelia arises from expansion of the central canal, either from forces acting from above or below. On the other hand, proponents of other theories suggest that the pathogenesis of syringomyelia is determined by a mechanism external to the spinal cord and that the fluid comprising the syrinx is CSF that has passed through the surface of the spinal cord along many microscopic paths, enlarging the syrinx from without, not from within. Thus, the theories of Ball and Dayan1 and Oldfield, et al.,16 argue that episodic elevations of either spinal venous pressure or pulse pressure in the subarachnoid space, respectively, propel the CSF through the Virchow–Robin spaces and the extracellular space of the spinal cord and into the syrinx. These latter theories, unlike the former, imply that spinal cord swelling and edema potentially predate the development of a syrinx cavity. However, this stage in the development of a syrinx has not been previously noted in a patient with a Chiari I malformation and syringomyelia. We present a patient with a Chiari I malformation in whom serial MR images obtained over a 3-month period document swelling and edema of the spinal cord that preceded development of a well-defined syrinx. Spinal cord edema in this case is consistent with transmural passage of CSF from the spinal subarachnoid space into the spinal cord.1,16 The notion that spinal cord edema develops into a syrinx is not explained by theories of syrinx pathogenesis in which it is postulated that syrinx fluid originates from the fourth ventricle via the central canal of the spinal cord4,5, 18–20 or results from obstruction of CSF passage within the central canal.13–15 Because treatment with craniocervical decompression and duraplasty in this case, which opened the CSF pathways at the foramen magnum, produced resolution of the spinal cord edema and syringomyelia, the CSF block at the foramen magnum is implicated as the cause of the spinal cord edema. The theory that the cerebellar tonsils act as a piston on a partially enclosed cervical subarachnoid space, creating enlarged cervical subarachnoid pressure