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

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 &levator ani

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

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

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

10. Coronal
Axial

11. pathogenesis

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

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

15. Imaging techniques

16. Imaging techniques
Fistulography
Endosonography CT
MRI

17. Perianal fistulography

18. Anal endosonography

19. CT

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

21. T2W  anatomy
T2W with fat sat ---- fistula

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

23. 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

24. 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

25. classification

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

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

28. 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 ischeorectal fossa
Grade 5 : supralevator & translevator fistula

29. Grade 1 : simple linear intersphincteric fistula

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

33. Intersphincteric fistula

34. Perianal fistula with an abscess

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

36. Grade 3 : transspincteric fistula

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

39. Transsphincteric fistula at 11 o’clock

40. Grade 4: transsphinteric fistula with abscess or2ry track within ischeorectal fossa

43. Grade 5 : supralevator & translevator fistula

44. 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)

45. Extrasphincteric fistula
A small abscess in left ischeoanal fossa , the fistula runs through levator ani , it is therefore above the sphincter complex and extrasphincteric

46. 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

47. Differential diagnosis

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

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

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

51. references

52. Goodsall DH, Miles WE. Diseases of the anus and rectum
Goodsall DH, Miles WE. Diseases of the anus and rectum. London, England: Longmans, Green, 1900.
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↵ Weisman RI, Orsay CP, Pearl RK, et al. The role of fistulography in fistula-in-ano: report of 5 cases. Dis Colon Rectum 1991; 34:
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54. Koelbel G, Schmeidl U, Majer MC, et al
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↵ Hussain SM, Stoker J, Schouten WR, Hop WCJ, Lameris JS. Fistula-in- ano: endoanal sonography versus endoanal MR imaging in classification. Radiology 1996; 200:
↵ Halligan S, Bartram CI. MR imaging of fistula-in-ano: are endoanal coils the gold standard? AJR Am J Roentgenol 1998; 171:
↵ Spencer JA, Chapple K, Wilson D, Ward J, Windsor ACJ, Ambrose NS. Outcome after surgery for perianal fistula: predictive value of MR imaging. AJR Am J Roentgenol 1998;

55. Thank you