The concept of tethered cord syndrome in veterinary medicine is somewhat ambiguous, having only been described in the context of an abnormal fixation of the filium terminale within the vertebral canal. As in human medicine, this term should be applied to any form of abnormal constriction of spinal cord movement within its meningeal covering. Tethering of the spinal cord simply means that the cord itself is tethered or “stuck” to the outer meninges (dura-arachnoid) and can be due to a number of causes (e.g., developmental, post-traumatic, post-inflammatory).
If a boulder is placed in the middle of a stream, the water will experience turbulent flow as is navigates around the obstruction. Similarly, normal cerebrospinal fluid (CSF) flow will undergo turbulence if obstructed at the site of spinal cord tethering. This turbulent flow can lead to disruptive forces on the spinal cord parenchyma which in turn can lead to focal syrinx formation (Fig-sagittal human MR with tethered cord). Treatment of this condition is typically surgical, via removing the adhesions between the spinal cord and outer meninges and re-establishing normal CSF flow. Other methods of surgical treatment employ shunts from the syrinx cavity into either the pleural or peritoneal cavities.
Tethered cord syndrome is not well-documented in canine patients. However, we occasionally encounter dogs with focal syringomyelia that do not have convincing MRI evidence of a causative craniocervical junction abnormality. We suspect that some of these dogs may have tethered cord syndrome. Because of the size of our patients, it may be difficult to verify cord tethering on static MR images, even with a 3.0 Tesla magnet. Current plans are to use cine-MRI or CSF flow studies in order to ascertain if there is, indeed, a focal obstruction to CSF flow in cases of focal syrinx formation with no craniocervical junction abnormality.