A magnetic resonance imaging study shows that I have a gas-filled cyst in my spine. My doctor now wants to do a computed tomography scan with myelography, and a discography. Are these really necessary?

While rare, gas-filled cysts in the spine can be rather small, even though they may produce significant symptoms. A CT myelogram is better than MRI at defining the lesion. Discography is the only method that can determine if there is communication between the disc space and the cyst.