IMAGING OF PERIANAL FISTULA MRI-U/S,FISTULOGRAM

1. Imaging of fistula in ano
Assisstent.Proff.Dr.Riyadh W. Al Esawi
College of Medicine –University of Kufa

8. Fistula in ano
Fistula is an abnormal connection between
the epithilialised surface of the anal canal
and the skin.
Sinus is a tract leading to or from a
suppurative cavity.

9. CAUSES
1- Infection of anal glands
2-Chrons disease
3-Ano-rectal malignancy
4- Radiation
5- Diverticulitis
6-Actinomycosis
7-Chlamydia
8-Lymphogranulomatous venereum
9-Syphlis
10-TB
11-HIV

10. Surgical classification : The Parks classification
1- Intersphincteric (~70%): fistula crosses the
intersphincteric space and does not cross the
external sphincter
2- Transsphincteric (25%): fistula crosses from
the intersphincteric space, through the external
sphincter and into the ischiorectal fossa
3- Suprasphincteric (5%): fistula passes
superiorly into the intersphincteric space, and
over the top of the puborectalis muscle then
descending through the iliococcygeus
muscle into the ischiorectal fossa and then skin
4- Extrasphincteric (1%): fistula crosses from the
perineal skin through the ischiorectal fossa
and levator ani muscle complex into the rectum
(i.e. it is outside the external anal sphincter)

11. Radiological classification: St James’s University
Hospital classification .
grade 1: simple linear intersphincteric
grade 2: intersphincteric with abscess or secondary
tract
grade 3: transsphincteric
grade 4: transsphincteric with abscess or
secondary tract within the ischiorectal fossa
grade 5: supralevator and translevator extension

17. Imaging modalities
• Fistulogram
• CT- Fistulogram
• MRI&MR Fistulogram +Endo anal MRI
• U/S-
Endo anal EA-U/S
T.V U/S
Trans-perineal
Infusion of hydrogen peroxide
Doppler study

18. MRI
MRI is the imaging modality of choice.
Active fistulous tracts are typically:
T1: isointense to muscle
T2: high signal compared to fat
T2-FS: high signal compared to fat
T1 C+: enhancing
Old, healed fistulae typically demonstrate low T1
and T2 signal without contrast enhancement,
reflecting fibrosis.

19. Fine 3 mm slices
•Axial and coronal T2 FS
•Axial and coronal T2 are helpful in the
the delineation of sphincter anatomy.
Best sequences to delineate the fistula:

20. We use a sagittal T2
single shot image
with centerline along
anal canal serving as
a localizer for the
subsequent
sequences.
Orientation of the
scanning planes
should be either
perpendicular or
parallel to the anal
canal

21. Suggested orientation for
axial MR imaging of the
anal canal. Sagittal T2-
weighted image through
the midline is used to
obtain images that are
Suggested orientation for
coronal MR imaging of the
anal canal. Coronal MR
imaging is performed at 90°
relative to the axial plane to
obtain images parallel to the

22. CLOCK SCHEMATIC FOR REPORTING
Supine position

23. RADIOLOGICAL REPORT
• detection of the primary fistulous tract and its activity:
– active tract has high T2 signal and demonstrates intense enhancement
– chronic tracts have low signal on both T1- and T2-WI and will not show
contrast enhancement
• location (right/left) and course
• relationship to the sphincter complex
– Parks classification: trans-, inter-, supra-, or extrasphincteric
• distance of the internal mucosal defect to the perianal skin on coronal
images
• position of the internal mucosal opening on axial images
– use the "anal clock": anterior = 12 o'clock
• identify secondary fistulous tracts and the sites of any abscess cavities in
order to avoid therapeutic failure and recurrence
• cranial extension above the levator ani muscle

24. MR -ANATOMY

25. MR-ANATOMY

27. Grade 1: simple linear intersphincteric fistula. (a) Drawing of the
anal canal in the axial plane shows a simple intersphincteric
fistula at the 2-o'clock position (arrow). (b) Axial contrast-
enhanced fat-suppressed T1-weighted MR image shows the left
intersphincteric fistula (arrow) bounded by the external
sphincter without a secondary fistulous track or abscess.

28. Axial T2-weighted images with fat suppression (STIR) at two
different levels (a, b). The dotted arrows demonstrate the inter-
sphincteric fistula and its extension to the skin (solid arrow)

29. Grade 2: intersphincteric fistula with an abscess. (a) Axial drawing of the anal
canal shows a right posterolateral abscess (arrow). (b) Axial contrast-enhanced
fat-suppressed T1-weighted MR image shows the abscess in the right
posterolateral aspect of the intersphincteric space (arrowhead), bounded by the
external sphincter.

30. Grade 3: transsphincteric fistula. (a) Axial drawing of the anal canal shows a
posterior transsphincteric fistula (arrow) with the internal opening at the 6-
o'clock position. (b) Axial contrast-enhanced fat-suppressed T1-weighted MR
image shows the transsphincteric fistula (arrow) crossing the external sphincter.

31. Grade 4: transsphincteric fistula with an abscess or secondary track in the ischiorectal or
ischioanal fossa. (a) Axial drawing of the anal canal shows a posterior transsphincteric
fistula with an abscess in the right ischiorectal fossa. (b) Axial contrast-enhanced fat-
suppressed T1-weighted MR image shows the posterior transsphincteric fistula (straight
arrow), the abscess in the right ischiorectal fossa with nonenhancing pus in the cavity
(arrowheads), and a secondary extension in the left ischiorectal fossa (curved arrow).

32. Both inter-sphincteric and trans-sphincteric components. An axial T2-weighted and three
consecutive thin slice (1 mm) T1-weighted images with fat-saturation after gadolinium contrast.
Images show inter-sphincteric fistula (white arrows). There is a thin communicating fistula
stretching in the inter-sphincteric plane (thin hatched arrow), going through the external
sphincter to reach the fistula lying outside the external sphincter (dotted arrow)
C0MPLEX FISTULA

34. Horseshoe fistula in the intersphincteric plane on an axial T2-weighted image.
The internal opening is located at 5–6 o’ clock as a thin white extension (white
arrow). The left fistula is more an abscess with debris and extension beyond the
external sphincter (black arrow)

35. Grade 5: supralevator and translevator disease (a) Coronal drawing of the anal canal
shows the left supralevator abscess with a left translevator fistula. (b) Coronal
contrast-enhanced fat-suppressed T1-weighted MR image shows the left
supralevator abscess with inflammatory changes surrounding the rectum and the left
translevator fistula crossing the ischiorectal fossa (arrowheads).

36. Two axial T2-weighted images (a, b) demonstrate thick fistula tracks
(black arrows) lying between rectal muscular wall and the pelvic floor
just above the puborectalis muscle. The internal opening is seen as a
large opening into the dorsal aspect of anorectal junction (white
arrow)

37. Sagittal T2-weighted image (a) and T2-weighted coronal image with fat-saturation (b) show an
abscess (thick white arrows on a and b) at the level of anorectal junction. There is blind sinus
(thin white arrow) extending upward above the pelvic floor. Consecutive coronal T2-weighted
images (c–f) show extension of the abscess in the inter-sphincteric planes bilaterally down
SUPRASPHENECTERIC
FISTULA

38. MR Pelvis FS T2W. a–c Axial and d coronal image of a
complex fistula showing transsphincteric track with
gluteal abscess (yellow arrows)

39. MR Pelvis FS T2W. a, b Coronal images and c, d axial
images of a complex transsphincteric fistula with
intersphincteric horseshoe extension (marked by yellow
arrows) and inflammation in adjacent ischioanal fat

40. MR pelvis images of a transsphincteric fistula with bilateral intersphincteric
extension. a, b T2W axial, c, d FS T2W axial, and e, f FS T2W coronal images
showing the course of track and extension (yellow arrows)

41. EA OR TR U/S
3D TRUS image of intersphincteric fistula (hypoechoic area marked by the yellow
arrow) at mid anal canal level. Red arrow demonstrates the hypoechoic internal
sphincter ring (imaging performed with BK medical 3D Endoanal USG transducer
Type 2052 with Flex focus scanner Type 1202)

42. Section of 3D TRUS image of transsphincteric fistula (yellow arrows) with
supralevator extension (red arrows) through the right intersphincteric plane.
Blue dotted line marks the level of the anorectal junction and the blue
arrows mark the levator plate

43. EA U/S

48. Transcutaneous U/S

51. 3D EA U/S

52. Transperineal U/S showing whole length of intersphincteric fistula
And its internal opening

53. Posterior intersphincteric
fistula with 3D surface
rendering

55. FISTULOGRAM

56. CT- FISTULOGRAM
CT fistulogram of a transsphincteric fistula in ano on the right perianal region
with upper and lower arms and internal openings in both anterior and posterior
midline. a Transverse image showing lower arm of the track entering into the anal
canal posteriorly (yellow arrow) with contrast in the rectum (blue
arrow). b Coronal image showing upper arm of the track entering into the anal
canal anteriorly

57. Secondary tract. (A) Sagittal thick MIP image showing
multiple branching tracts. (B) VRT image showing all
branches of the tract.

58. a Plain X-ray pelvis (AP view) demonstrating gas shadow on the right perianal
and gluteal region (white arrow). b X-ray fistulogram (Deshpande’s technique)
of the same patient showing abscess cavity filled with radio-opaque contrast
extending towards right gluteal region (white arrow) with gas-filled in the
rectum (yellow arrow)

59. X-ray fistulogram of a semi-horseshoe fistula showing Deshpande’s
technique of double-contrast fistulography with malecot rubber catheter
in the anorectal canal to fill air into the rectum (yellow arrow) with a
metal marker at anal verge (white arrow). Blue arrow demonstrates the
level of the anorectal junction

60. X-ray pelvis with fistulogram (AP view) showing contrast material
in the portal venous circulation (yellow arrows) due to forceful
injection of contrast material into the fistulous track (white
arrow)

61. Best wishes