Sacroiliac pain most commonly originates from the lumbar spine and normally from nerve root compression. I would advise a lumbar spine MRI to help diagnose the origin of the pain. Tarlov cysts are quite common and only rarely cause pain. Can you see at least the lower disc or two (L5-S1 or L4-5) from this sacroiliac MRI?
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.