Of the nonrandomized patients in the observational study group , 5 ( 24 % ; 95 % CI , 6 % -42 % ) who underwent biliary sphincterotomy , 12 ( 31 % ; 95 % CI , 16 % -45 % ) who underwent dual sphincterotomy , and 2 ( 17 % ; 95 % CI , 0 % -38 % ) who did not undergo sphincterotomy had successful treatment .