Syringomyelia without hindbrain herniation: possible tight cisterna magna

This is 54 year old male.  There is a long segment syringomyelia but no signficant hindbrain herniation. However, if you note the subarachnoid space anterior to the brainstem at the level of the foramen magnum is open but the cisterna magna is impacted by the tonsils, a condition which has been termed "tight cisterna magna."  Syringomyelia associated with tight cisterna magna should not be classified as idiopathic syringomyelia; rather, it belongs to the category of organic syringomyelia such as Chiari malformation.   Contrast study was also suggested in this case to r/o alternate etiologies. 

Further reading suggested: 

J Neurosurg. 2002 Mar;96(2 Suppl):239-49. Syringomyelia without hindbrain herniation: tight cisterna magna. Report of four cases and a review of the literature. Kyoshima K, Kuroyanagi T, Oya F, Kamijo Y, El-Noamany H, Kobayashi S.