Features of spontaneous improvement in syringomyelia with low-situated cerebellar tonsils.

We analysed four patients who showed spontaneous improvement among the 19 nonsurgically treated cases of syringomyelia with low-situated cerebellar tonsils who visited our outpatient clinic. MR images both before and after improvement were available for two of these patients; CT-myelography before improvement and MR images after improvement were used for two patients. Consequently, we were able to abstract several features from detailed and precise neurological and radiological evaluations of these patients. These features consisted of mild (rather than severe) disability, as well as three radiological features--a rounded shape of the lower edge of the cerebellar tonsils, a low tightness of the foramen magnum, an elevation of the tonsils during the course of the disease. Results of our radiological analyses were consistent with the theories proposed for the pathogenesis of syringomyelia in the light of the CSF flow around the foramen magnum. We propose that the features we have isolated are useful in determining treatment policies and prognoses of patients with syringomyelia, accompanied by low-situated cerebellar tonsils.