Synovial cysts, cysts that appear on the synovium or lining of a joint, can appear on the spine, which is a whole bunch of joints, one on top of the other. They are more frequently found in wrists, ankles and feet, but can occur anywhere. They are fluid filled masses, or sacs, that are caused by irritation. Depending on the cause of the cyst, it could be that the fluid is building up to try to protect the joint from bone rubbing on bone.
The cysts may cause pain or disability – it could affect the nerves going down from the back, depending on where in the back the cysts are. Some people feel back pain, leg pain, numbness in the legs and/or feet, or even inability to control bowel and/or bladder.