Idiopathic syringomyelia and the importance of occult arachnoid webs, pouches and cysts.

Syringomyelia is the condition in which longitudinal cavities are found within the spinal cord. The use of drainage procedures has been widely practised with good short term results. However, the long-term results in some large series have been less favourable. There are many associated conditions and in most forms a blockage to the normal flow of CSF, either at the foramen magnum or in the spinal canal, can be identified. Most surgeons would now direct their efforts to the establishment of normal CSF flow rather than a shunting procedure. In a certain group of patients, even with the advent of sophisticated MRI, no associated abnormality or CSF block is easily identified. This type of syringomyelia is often termed idiopathic. We report 10 patients with symptomatic syringomyelia without readily recognized predisposing factors. In eight patients preoperative myelography revealed a block to the flow of contrast compatible with subarachnoid obstruction. Eight patients underwent laminectomy and division of the obstructing arachnoid webs. Five experienced good improvement and three only moderate improvement. Two of the patients underwent syrinx shunting procedures only, which resulted in a worsening of their symptoms. At operation one patient was found to have an arachnoid cyst. We believe that patients with idiopathic symptomatic syringomyelia may need myelography to identify such arachnoid abnormalities. Subsequent surgery should be directed at the establishment of normal CSF flow by laminectomy and excision of the offending lesion.