Current theories on the causes of syringomyelia have only one aspect in common, namely that syringomyelia results from cerebrospinal fluid (CSF) flow obstruction in all diseases associated with syringomyelia. Tethered cord syndrome is known to cause syringomyelia also in the absence of an obstruction to cranial-to-spinal CSF flow. We conducted this study to investigate this phenomenon in our patient population. We included not only patients with primary tethered cord syndrome but also patients with (posttraumatic or postoperative) secondary tethered cord syndrome although (or because) these patients have both CSF flow obstruction and tethered cord syndrome.
From 2003 to 2018 we diagnosed in 45 patients primary tethered cord syndrome. All underwent cardiac-gated phase-contrast magnetic resonance imaging (MRI) of CSF flow pulsation of the whole spine and the brain.
In patients with primary tethered cord syndrome, CSF flow obstruction similar to that seen in association with intradural adhesions was detected only in the presence of diastematomyelia (12 patients). In patients without tethered cord syndrome, no relevant CSF pulsation was noted below lumbar vertebra 1 (L1). In patients with tethered cord syndrome and a low-lying conus, however, relevant pulsations were also detected in the lumbar subarachnoid space similar to the pulsations seen in the region of the lower thoracic spine in patients without a low-lying conus. Particularly important information on the aetiology of syringomyelia was obtained from a patient with posttraumatic syringomyelia and an untreated fracture-dislocation with a complete blockage of the spinal canal and thus with a complete obstruction of CSF flow. He developed marked syringomyelia in the region of the thoracic spine in spite of the complete absence of pulsation cranial to the syrinx. A decrease in syrinx cavity size after an untethering procedure in primary tethered cord syndrome is evidence of a causal role.
Apart from brain pulsation, spinal cord pulsation decisively contributes to the development of syringomyelia in some groups of patients. Cranial pulsation appears to play a less important role in these cases.