Fig. 3

Anal fistula MRI-defined dentate line measurement. A, B are schematic diagrams of the determining dentate line on MRI, respectively. A The position of the internal opening of the cross section (arrow). B is a schematic diagram of a coronal image. Where S is the distance between the internal opening measured by the surgeon and the dentate line; R is the linear distance between the internal opening measured by the diagnostician and the anal verge (the underside of the external sphincter skin); and L is the distance between the dentate line and the anal verge (L = R–S). C, D are corresponding measurement methods on MRI images. C The dynamic contrast-enhanced fat-saturated T1-weighted MR image and D is coronary T2WI image, respectively