mri of fistula in ano - acpgbi · mri of fistula in ano dr damian tolan st james’s university...
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MRI of Fistula In Ano
Dr Damian Tolan St James’s University Hospital – Leeds
ACPGBI Edinburgh 2015
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Objectives
• To understand how radiologists perform, interpret and report fistula MRI
• To learn MRI signs of disease activity and implications of MR findings in surgical treatment planning
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Problems surgeons encounter…
• The current Gold Standard is surgical assessment
• Examination under Anaesthesia (EUA)• This isn’t perfect…
2,500 years progress
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Problems surgeons encounter…
1. don’t appreciate the fistula course2. fail to appreciate complex features
• pockets of undrained sepsis• fail to recognise complications
How does MRI influence outcome…?
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What do we know? Recurrent disease
Recurrent fistula in ano• Surgeon always acts on MRI results
recurrence rate=16%• Surgeon never acts on MRI results
recurrence rate=57%
Surgery guided by MRI reduces further recurrence by 75%
BUCHANAN Lancet 2002
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What do Surgical guidelines say?
Position Statement ACPGBI* (2007)• MRI should be considered in any primary
fistula deemed after clinical or endosonographic assessment to be complex
• Should also be considered in patients with recurrent anal fistula
• MRI is superior to ultrasound*(Association of ColoProctologists of Great Britain and Ireland)
WILLIAMS Dis Col Rect 2007
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Understanding fistulas
• How do we do our MRI?
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MRI Hardware requirements
1.5T MRI• Multichannel surface coil• Endoluminal (anal) coil unnecessary
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MRI OrientationImage © Springer
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MRI Technique
Imaging planes• Axial - relationship to
sphincters• Coronal - level of internal
opening & relationship to levator ani muscles
Sagittal sometimes useful (e.g. anovaginal fistula)
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MRI Orientation
True height with oblique coronalForeshortening without obliqueImage © Springer
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MRI Sequence selection
Personal preference�Fistula scan�(3-5mm slice thickness)Choices –• STIR•T2 with fat saturation
•T1 with fat saturation post gadolinium
Oedema sequences
Enhancement sequences
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MRI Sequence selection
STIR/T2 FS• Simple• No injection• Inflammatory tracks �bright�
T1FS +gad
STIR
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MRI Sequence selection
STIR/T2 FS• Fibrotic areas dark
STIR
OEDEMAbefore fistula plug
FIBROSISafter fistula plug
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MRI Sequence selection
STIR/T2 FS• BUT thin tracks
not always easy to see
STIR
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MRI Sequence selection
STIR/T2 FS• Granulation tissue vs. fluid
can be difficult
Chronic fistula with dark fibrotic ring
STIR
Chronic fistula –
?fluid collection
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MRI Sequence selection
T1 FS with Gadolinium• Injection required• Inflammatory tracks �bright�
• Fibrotic areas/fluid dark• Good for granulation vs.
fluid (e.g. Crohn�s disease Rx)
T1FS +gad
Chronic fistula
enhancing granulation tissue
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MRI STIR vs T1 +gad
Undercall with STIR alone• ? Fistula• Difficult to see on STIR• More conspicuous with
T1 +gad • Both seen and treated at
EUA
T1FS +gad
STIR
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MRI STIR vs T1 +gad
Overcall with Gad• ?residual �Fistula� 12
months post mucosal advancement flap
• No fluid on STIR• Patient assymptomatic on
follow up• EUA - nil to find
T1FS +gad
STIR
No fistula - enhancing inflammatory track
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MRI STIR vs T1 +gad
Fluid vs. inflammation• Crohn�s disease ? For infliximab
? fluid collection Enhancing granulation tissue - No collection
T1FS +gadSTIR
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MRI STIR vs T1 +gad
Fluid vs. inflammation• Crohn�s disease ? For infliximab
? fluid collection Non enhancing fluid collection confirmed
T1FS +gadSTIR
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• Complex/recurrent disease• Crohn�s disease assessment• In combination with STIR/T2 FS
Role of T1FS +gadolinium
? fluid collection Non enhancing fluid collection confirmedT1FS +gadSTIR
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Understanding fistulas
• Anatomy critical
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Sir Alan Parks 1920-1982, Royal College of Surgeons England
Understanding fistulas
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Prof Steve Halligan
University College Hospital
London
Understanding fistulas
Dr John SpencerSt James’s University Hospital
Leeds
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MRI – Levator Ani
Image © Springer
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MRI - Puborectalis
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MRI - Puborectalis
• Puborectalis - U or V shaped sling• Important landmark - Dentate line
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MRI - Puborectalis
• Puborectalis - U or V shaped sling• Important landmark - Dentate line is just caudal
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MRI – Dentate line
• Dentate line invisible on MRI• ~2cm from anal verge, mid canal
2cm
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MRI - Intersphincteric plane
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Intersphincteric plane & PathologyWhy important?• Focus for interpretation
Gluteus maximu
s
Ischioanal fossa
e x t
p r
i nterna l
obt’r internus l
ev
ani
X
T1FS +gadSTIRFocal inflammation in neutropenia
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Intersphincteric plane & PathologyWhy important?• Focus for interpretation
Gluteus maximu
s
Ischioanal fossa
e x t
p r
i nterna l
obt’r internus l
ev
ani
X
T1FS +gadSTIR
Focal intersphincteric abscessPersistent pain – nil clinically
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Reporting findingsMy approach…
Paul Delaroche
“Un bon croquis vaut mieux qu'un long discours”
“A good sketch is better than a long speech”
Attributed to N Bonaparte
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Reporting findings
1. What is it? Fistula or something else?• Blind sinus / Abscess / Pilonidal Sinus
Separate from sphincters
Pilonidal sinus
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Reporting findings
2. What type of fistula?• Inter/Trans/Supra/Extrasphincteric
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Reporting findings
3. Simple or complex?Simple transsphincteric Complex transsphincteric
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Reporting findings
4. Step by step – Internal opening• Height and clock position
Visible defect – 6 o/c Predicted defect – 6 o/c
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Reporting your findings
5. Step by step – Path of the fistula• Intersphincteric / transsphincteric
Intersphincteric 6 o/c
Crosses sphincter High at 6-7 o/c
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Reporting your findings
5. Step by step – Path of the fistula• Suprasphincteric / extrasphincteric
•Position levator crossed? underlying aetiology
? Crohn’s? Malignancy
R
Extrasphinteric crosses levator at 7 o/c
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Reporting your findings
6. Step by step - External opening• Location and clock position
Natal cleft 6-7 o/c4cm from anal verge
Perineum 6 o/c1.5 cm from anal verge
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Reporting your findings
7. Step by step – Complex features•Extensions – number, location and
clock positionIntersphincteric horseshoe3-7 o/cMid canal
Ischioanal fossa4-5 o/cBlind ending
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Reporting your findings
8. Step by step – Complex features• Involvement of other structures
Osteomyelitis coccyx
Fistula to vagina12 o/c Lower canal
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MRI and surgical planning
• MRI findings can modify or delay surgery
• For assessment of persistent symptoms
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MRI and surgical planning
• Evaluate presence of sepsis before definitive intervention
Seton in high transsphincteric fistula
BUT large undrained supralevator extension
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MRI and surgical planning
• Is the seton in the right place?• Suprasphincteric (not trans)
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MRI and surgical planning• Mapping recurrence after failed
treatmentTranssphincteric fistula after fistula plug
Patent internal opening
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Conclusion
• MRI technique is important