Objective To investigate the application value of magnetic resonance imaging (MRI) examination in the efficacy evaluation of infliximab combined with seton placement for perianal fistulizing Crohn's disease (PFCD) and influencing factors of deep remission.Methods The retrospective case-control study was conducted.The clinicopathological data of 57 patients with PFCD who were admitted to the Affiliated Hospital of Nanjing University of Chinese Medicine from August 2010 to October 2017 were collected.There were 39 males and 18 females,aged (24±9)years,with a range of 14-58 years.Patients underwent MRI examination preoperatively and postoperatively.Observation indicators:(1) follow-up situations;(2) influencing factors analysis of deep remission of PFCD.Follow-up using outpatient and inpatient reexamination was performed to detect clinical recovery of patients up to October 2017.Measurement data with normal distribution were represented as Mean±SD.Measurement data with skewed distribution were described as M (range).Count data were represented as absolute number or percentage.The univariate analysis was performed using the chi-square test.The multivariate analysis was done using the logistic regression model,using P＜0.15 as an inclusion criteria in the univariate analysis.Results (1) Follow-up situations:57 patients with PFCD undergoing inflixmab combined with seton placement were followed up for (40±24)months.During the follow-up,24 of 57 patients had clinical response,33 had long-term clinical healing.The fistulas of 24 patients with clinical response presented as high signal on T2 weighted image (T2WI) of postoperative MRI.Of 33 patients with long-term clinical healing,the fistulas of 16 patients with deep remission presented loss of high signal and replacement of fibrosis tissue on T2WI of postoperative MRI,the fistulas of 17 patients without deep remission presented as high signal on T2WI of postoperative MRI.(2) Influencing factors analysis of deep remission of PFCD:results of univariate analysis showed that extent of fistula was related factors affecting deep remission of PFCD (x2 =4.312,P＜0.05).Results of multivariate analysis showed that a single fistula complicated with branches and times of infliximab maintenance treatment ≤3 were independent risk factors affecting deep remission of PFCD (odds ratio=4.377,4.296,95％ confidence interval:1.124-17.043,1.158-15.940,P＜0.05) and fistula under levator ani muscle was an independent protective factor affecting deep remission of PFCD (odds ratio =0.182,95％ confidence interval:0.041-0.815,P＜ 0.05).Conclusions Partial patients with long-term clinical healing can achieve deep remission after Infliximab combined with seton placement for perianal fistulizing Crohn's disease,requiring MRI examination to further evaluate recovery situations.A single fistula complicated with branches and times of infliximab maintenance treatment ≤ 3 are independent risk factors affecting deep remission of PFCD and fistula under levator ani muscle is an independent protective factor affecting deep remission of PFCD.