Gas-filled Intradural Cyst
The authors present two unusual case reports of patients who had severe sciatica symptoms. Imaging studies demonstrated gas-filled cysts that had migrated into the nerve root of the cauda equina. These findings are quite rare. Both patients underwent surgical laminectomy. This allowed removal of the cyst with decompression of the involved nerve root. Repair of the dura mater which covers the spinal cord was necessary due to its disruption.
Both patients had resolution of their severe sciatica symptoms following surgery.

While most gas-filled cysts in the spine are felt to be from herniated discs, there was no disc material found in the tissue removed during surgery in the two cases reported. The authors felt that likely the disc material had degenerated.

The authors believe that computed tomography myelography is preferred over magnetic resonance imaging for diagnosis of the cyst. Discography is felt to be the only method able to confirm communication between the disc space and the cyst.
Y. Kudo et al. Gas-filled intradural cyst with migration into the nerve root of the cauda equina. J Neurosurg Spine. May 2008. Vol 8. Pp. 482-486.