This is a cyst on the spinal cord, filled with spinal fluid. It may cause no pain. When it does cause pain, it may be because it is pressing on the spinal cord. According to a medical paper by Dehaine, intradural injections of corticosteroids provided lasting pain relief for one patient. Robin found that her pain was eliminated for 9 months at a time by corticosteroid injections before she was diagnosed as having large Tarlov's cysts.
Tarlov cysts can be seen on an MRI scan.
The cysts can be drained, but they usually fill up again. Injections of corticosteroids usually help. Surgery to remove the cysts is very difficult - one doctor described it as trying to sew wet tissue paper. There is a new operation using a 'glue' (based on the clotting factor in blood) to stick the tissue together so that the cyst doesn't fill up again.
There is a support group on this condition on Facebook.