What Doctor Do You See to Have a Episacroiliac Lipoma (Aka Back Mouse) Removed from the Lower Back?

My husband's back has been hurting him. He has seen a orthopedic surgeon and family practice doctor. Neither Doctor could identify the problem. While getting a massage we found that he had a small marble sized lump that could be felt in his lower left back just above his hip. Upon touching it he immediately felt more pain. We have done some research and have found that this is a problem which is not really recognized in the medical community and arent sure were to go for treatment.