Magnetic Resonance Imaging of Perianal Fistulas Poster No.: C-0317 Congress: ECR 2014 Type: Authors: Keywords: DOI: Educational Exhibit A. P. Sathe, E. Soh, K. Y. Seto, B. Yeh, D. W. Y. chee, R. Quah, S. Bhagwani, L.-A. Goh; Singapore/SG Fistula, Education, MR, Gastrointestinal tract 10.1594/ecr2014/C-0317 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.myesr.org Page 1 of 12
Learning objectives To describe the magnetic resonance imaging (MRI) features and classification of perianal fistulas. To discuss the role of MRI in the evaluation and management of perianal fistulas. Background Perianal fistula is an abnormal communication between the anal canal and the perianal skin. It is thought to be due to obstruction of the anal gland with secondary abscess formation and external rupture of the abscess. Other causes include Crohns disease, infections (viral, fungal and TB) and iatrogenic (hemorrhoid surgery). It is common condition that often recurs because of infection that was missed at surgery. Preoperative MR imaging due to its multiplanar capabilities and excellent soft tissue resolution helps to prevent recurrence by accurate assessment of disease extension and localization of primary tracks, secondary tracks and abscess formation. Surgically, the anal canal extends from the perineal skin to the anorectal ring, which lies at the upper border of the puborectalis muscle. The dentate line is the junction between the columnar epithelium of the proximal anal canal and squamous epithelium of the distal anal canal and lies at the mid-canal level. The anatomical anal canal extends from the perineal skin to the dentate line. The anal canal is surrounded by two muscular sphincters, the internal and external anal sphincters, which are composed of smooth and striated muscle, respectively (Figs 1 and 2). The external sphincter merges proximally with the sling-like puborectalis muscle, which itself merges with the levator plate of the pelvic floor. The internal sphincter is the distal termination of the circular muscle of the rectum. Images for this section: Page 2 of 12
Fig. 1: Fig 1.Coronal T2 weighted MRI image demonstrates sphincter complex and pelvic floor muscles. Page 3 of 12
Fig. 2: Axial T2 weighted image at the level of mid anal canal shows normal anatomy of sphincter complex. Page 4 of 12
Findings and procedure details Our pelvic MRI protocol for perianal fistula evaluation consists of T1W and T2W sequences without fat suppression in axial, coronal and sagittal planes for delineation of the sphincter anatomy and pelvic floor muscles, fat planes and the fistula tract. T2- weighted imaging with fat suppression is used to assess for edema and fluid containing tracts and cavities, whereas fat suppressed T1-weighted contrast-enhanced sequences are used to assess the presence and degree of inflammation. Fistulas can be classified into: 1. Intersphincteric fistula (45%): The most common type, in which the fistula only tracks to the intersphincteric space and is limited by the external sphincter (Fig 3). 2. Transsphincteric type (30%): The track passes through the intersphincteric plane and external sphincter into the ischiorectal fossa (Fig 4). 3. Suprasphincteric type (20%): The fistula extends superiorly within the intersphincteric plane to reach above the levator plate and then penetrate inferiorly through the ischioanal fossa and finally to the skin. Figure 5 shows a suprasphincteric fistula with translevator extension and abscess formation. 4. Extrasphincteric type (5%): This type results from extension of primary pelvic disease (eg: Crohn's disease, diverticulitis) down through the levator plate. This fistula lies completely outside the external sphincter complex. When describing the fistula during reporting, it is important to mention the position of the mucosal opening on axial images by using the anal clock (Fig 6), distance of the mucosal defect to the perianal skin on coronal images, and secondary fistulas and abscesses. Images for this section: Page 5 of 12
Fig. 1: Fig 1.Coronal T2 weighted MRI image demonstrates sphincter complex and pelvic floor muscles. Page 6 of 12
Fig. 2: Axial T2 weighted image at the level of mid anal canal shows normal anatomy of sphincter complex. Page 7 of 12
Fig. 3: contrast-enhanced fat-suppressed T1-weighted MR image shows an enhancing intersphincteric fistula (arrow) located at 6 o'clock on the left confined by the external sphincter. Page 8 of 12
Fig. 4: Axial contrast-enhanced fat-suppressed T1-weighted MR image shows a transsphincteric fistula (arrow) crossing the external sphincter with adjacent inflammatory changes in the left ischiorectal fossa. Page 9 of 12
Fig. 5: Coronal fat suppressed contrast enhanced T1 weighted MR image shows a left perianal fistula (arrow) with supralevator extension and associated abscess(arrowhead). Page 10 of 12
Fig. 6: Axial T2-weighted MR image shows the anal clock, for referencing the location of the anal fistula with respect to the anal canal. Page 11 of 12
Conclusion MRI is the imaging gold standard for preoperative evaluation of perianal fistulas. MRI provides superior definition of the fistulous track and allows identification of secondary fistulas or abscesses. Personal information Dr. Lesley-Ann Goh Hui Huan, Head of Department, Senior Consultant. Alexandra Hospital, Jurong health services. lesley_ann_goh@juronghealth.com.sg References 1. Rectum-Perianal Fistula, Susanne Tonino and Robin Smithuis, Radiology assistant,january 21, 2009. 2. MR Imaging Evaluation of perianal Fistulas: Spectrum of Imaging Features. de Miguel Criado J, del Salto LG, Rivas PF, del Hoyo LF, Velasco LG, de las Vacas MI, Marco Sanz AG, Paradela MM, Moreno EF. Radiographics. 2012 Jan Feb;32(1):175-194. Page 12 of 12