Abstract: Objective To investigate the application of dynamic contrast-enhanced magnetic resonance imaging(DCE-MRI) in preoperative evaluation of fistula and fistula orifice in patients with anal fistula. 
Methods A total of 90 patients with high complex anal fistula(HCAF) were selected, DCE-MRI was performed before operation, and magnetic resonance imaging(MRI) was performed 30 min after wards. The results of surgical and pathological diagnosis were taken as the gold standard to analyze its diagnostic efficacy. 
Results DCE-MRI diagnosis showed 91 primary fistulas, 135 > 5 mm branching fistulas, 121 ＜ 5 mm branching fistulas, 81 primary internal fistulas and 27 small internal fistulas in patients with HCAF. MRI gadolinium-fed fistula angiography and DCE-MRI diagnostic results showed that there were 92 main fistulas, 137 > 5 mm branching fistulas, 154 ＜ 5 mm branching fistulas, 87 main internal fistulas and 103 small internal fistulas in patients with HCAF. The accuracy rate of DCE-MRI in diagnosing primary fistula, > 5 mm branch fistula, ＜ 5 mm branch fistula and primary internal fistula in HCAF patients was 97.89%, 88.27%, 71.62% and 85.86%, respectively, and the Kappa value of consistency test with surgical pathology diagnosis was 0.657, 0.436, 0.422 and 0.454, respectively(P＜0.05). The accuracy rate of DCE-MRI in diagnosing small internal fistulas in patients with HCAF was 29.83%, and the Kappa value of consistency test with surgical pathology diagnosis was 0.040(P＞0.05). The accuracy of MRI gadolinium-contrast fistula+DCE-MRI in the diagnosis of primary fistula, ＞5 mm branch fistula, ＜5 mm branch fistula, primary internal fistula and small internal fistula in patients with HCAF was 98.95%, 89.51%, 75.55%, 89.90% and 71.82%, respectively, and the Kappa value of consistency test for surgical and pathological diagnosis was 0.795, 0.467, 0.433, 0.446 and 0.380, respectively(P＜0.05).  
Conclusion MRI gadolinium fistulography combined with DCE-MRI technology has an important application value in preoperative evaluation of small branch fistula and fistula orifice of HCAF. 

Key words: rectal fistula, magnetic resonance imaging, gadolinium fistulography