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MRI imaging of Perianal fistula

Dr. Ahmed Refaey , FRCR Consultant Radiologist Riyadh Military Hospital. MRI imaging of Perianal fistula. Format of the lecture. Anatomy Pathogenesis Imaging techniques Scanning protocoles Classification Examples. Anatomy . Anatomy .

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MRI imaging of Perianal fistula

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  1. Dr. Ahmed Refaey , FRCR Consultant Radiologist Riyadh Military Hospital MRI imaging of Perianal fistula

  2. Format of the lecture • Anatomy • Pathogenesis • Imaging techniques • Scanning protocoles • Classification • Examples

  3. Anatomy

  4. Anatomy • Anatomical canal : - extends from perineal skin to dentate line • Surgical canal : - extends from perineal skin to anorectal ring ( 1-1.5cm abov e dentate line ) - total length 4-5 cm

  5. Anal sphincter comprised of 3 layers • Internal sphincter - continuance of circular smooth muscle of rectum, involuntary, contracts at rest & relaxes at defecation • Intersphincteric space • External sphincter - voluntary striated muscle , continuous cranially with puborectal muscle &levatorani

  6. Puborectal muscle has its origin on both sides of the symphysis pubis, forming a sling around the anorectum

  7. The puborectal muscle is contracted at rest and accounts for the 8O0 angulation of the anorectal junction . It relaxes during defecation

  8. On axial and coronal MR images , the different layers of anal sphincter and the surrounding structures can be displayed perfectly

  9. Coronal Axial

  10. pathogenesis

  11. Perianal fistula • Abnormal connection between the epithilialised surface of the anal canal and the skin.

  12. Causes • 1ry - obstruction of anal gland which leads to stasis & infection with abscess & fistula formation ( most common cause ) • 2ry - iatrogenic ( post hemorrhoiedalsurgury ) - inflammatory bowel dis. ( crohn’s disease ) - infections ( viral , fungal or TB ) - malignancy

  13. Imaging techniques

  14. Imaging techniques • Fistulography • Endosonography • CT • MRI

  15. Perianalfistulography

  16. Anal endosonography

  17. CT

  18. MRI protocol • T1W &T2W fse axial and coronal • T2W with fat sat • T1W + CM • FOV 200

  19. T2W ----- anatomy • T2W with fat sat ---- fistula

  20. The anal clock P: anterior perineum n: natal cleft

  21. The anal clock • The surgeon’s view of the perianal region when the patient is in the supine lithotomy position , corresponds to the orientation of axial MRI of the perianal region

  22. Reporting • Position of the mucosal opening on axial images using anal clock • Distance of mucosal defect to perianal skin on coronal images • 2ry fistulas or abscess

  23. classification

  24. Classification • Parks classification 1- intersphincteric 2- transsphincteric 3- extrasphincterisc 4-suprasphincteric Intersphincteric & transsphincteric are the most common Intersphincteric --> 70 % Transsphincteric -->20%

  25. St. James university hospital classification MR imaging Grading of perianal fistulas

  26. MRI Grading of perianal fistulas • Grade 1 :simple linear intersphincteric fistula • Grade 2 :intersphincteric fistula with abscess or 2ry track • Grade 3 :transsphincteric fistula • Grade 4:transsphinteric fistula with abscess or2ry track within ischeorectalfossa • Grade 5 :supralevator & translevator fistula

  27. Grade 1 :simple linear intersphincteric fistula

  28. Intersphincteric fistula • Axial T2W with and without fat saturation • The intersphincteric fistula located at 6 o’clock

  29. Intersphincteric fistula

  30. Perianal fistula with an abscess

  31. Grade 2 :intersphincteric fistula with abscess or 2ry track

  32. Grade 3 :transspincteric fistula

  33. Transsphincteric fistula • The defect through internal & external sphincter at 6 o’clock is clearly visible

  34. Transsphincteric fistula at 11 o’clock

  35. Grade 4:transsphinteric fistula with abscess or2ry track within ischeorectalfossa

  36. Grade 5 :supralevator & translevator fistula

  37. Suprasphincteric fistula • Two tracts in ischeorectal region • The right sided tract runs over the puborectal muscle (asterisc) & the mucosal opening lies at the level of dentate line (black arrow)

  38. Extrasphincteric fistula • A small abscess in left ischeoanalfossa , the fistula runs through levatorani , it is therefore above the sphincter complex and extrasphincteric

  39. Complex fistula • 2 tracts in left buttock form single tract • The fistula breaks through the external sphincter • In intersphincteric space it divides again into 2 tracts • One ends blindly in the intersphincteric space • The other breaks through the internal sphincter with mucosal defect at 1 o’clock

  40. Differential diagnosis

  41. Pielonidal sinus • Small abscess just above the nates • No relation with sphincter complex

  42. Proctitis • No fistula was seen • Diffuse thickening of rectal mucosa due to proctitis

  43. Ischiorectal space abscess • An abscess in ischiorectal space with no connection to the sphincter complex

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