Reply

We appreciate Dr. Olivero's letter and his interest in our article. In their paper (1), Drs. Olivero and Dinh describe a patient with post-traumatic acquired Chiari I malformation and syringomyelia that spontaneously resolved without intervention. They review multiple theories of the pathogenesis of syringomyelia and hypothesize that head trauma in this 28-year-old woman resulted in elevated intracranial pressure and secondary tonsillar herniation that then led to obstruction of CSF flow at the level of the foramen magnum. They hypothesize that this resulted in elevated pressure in the spinal subarachnoid space, preventing egress of fluid normally produced in the spinal cord and resulting in syrinx formation. When the elevated intracranial pressure resolved, normal CSF flow across the foramen magnum was reestablished, and the syrinx resolved.

We appreciate Dr. Olivero's emphasizing that the source of CSF within hydromyelic cavities associated with the Chiari I malformation is controversial and by no means firmly established. He reviews the evidence that, in the context of a Chiari I malformation and accentuation of systolic pressure waves within the spinal subarachnoid space, CSF may not be driven into the spinal cord parenchyma along the perivascular spaces. Rather, the CSF produced within the cord substance may be prevented from exiting because of elevated pressure in the spinal subarachnoid space. We failed to mention this theory in our report (2). Nonetheless, if true, this theory regarding the directionality of CSF flow is not inconsistent with our hypothesis that a presyrinx state may depend upon the patency of the central canal and, more importantly, is associated with CSF obstruction which, if relieved, may reverse the condition.