MRI of fistula in ano

C HOEFFEL

JM TUBIANA

• Describe the impact of MRI in the management of fistulas

• Propose protocols and report forms used for fistula in ano evaluation

Objectives

Fistula in ano

•  Track communicating with the rectum or the anal canal via an internal opening and generally with an external opening

•  Infection of an

intersphincteric gland-followed by drainage of the abscess in every directions

WHY MRI ?

• MRI versus clinical examination versus endoanal ultrasound – 104 patients evaluated with the three

modalities and follow-up (MRI or surgery) as the gold standard.

• MRI versus Clinical examination – Correct classification 90 vs 61 % – Best for detection of abscesses, of

horseshoe fistulas

Buchanan Radiology 2004

• MRI versus endoanal ultrasonography –  Internal opening 97 vs 91 % –  Best detection of complex tracts and

abscesses with MRI

WHY MRI ?

Buchanan Radiology 2004

• First suspicion of fistula –  30 patients with pre-operative MRI, surgery and rectal exam under GA + follow-up with surgery and 12 months MRI. Disagreement n=15 • Minor disagreement , n=12 • Change in management, n=3 • MRI ‘s impact on treatment decisions = 10 %

Buchanan Br J Surg 2003

WHY and WHEN MRI ?

• Recurrent Fistula 71 patients – Agreement surgery/MRI, n=40

• 5 with recurrent fistulas – Discrepancies surgery/ MRI, n=31

• 16 with recurrent fistula (52 %), p=0.0005, at the location predicted by MRI

• MRI guided surgery decreases recurrence rate down to 75 %.

Buchanan Lancet 2002

WHY and WHEN MRI ?

• Endoscopic Ultrasonography –  Particularly for intersphincteric fistulas –  Less accurate in case of sepsis or complex

fistulas

• MRI – First-step examination in case of recurrent

fistula – If presence of a complex fistula at US or

clinical examination – Before anti-TNF treatment

Williams Dis Colon Rectum 2007

WHY and WHEN MRI ?

• Technique • Anatomy • Classification

MRI : HOW ?

MRI Technique

• Sequence Selection • Planes • Slices orientation

MRI Technique

• 1.5 Tesla ou 3 T • Phased-array coil, without any preparation nor endorectal probe.

Sequences

–  Anatomical views Sag T2 - Ax T2 Pelvis –  Fistula imaging

• STIR • Fat Suppressed T2 • Gado Fat suppressed T1 3 DT2 w-TSE with post processing reformation ?

How to choose sequences ?

• T2 FS / STIR –  Simple –  No injection –  High signal intensity of the

inflammatory tract –  Fibrous areas low signal

intensity –  Less sensitive for very thin

tracts –  Difficult to differentiate

inflammation from fluid

HALLIGAN Radiology 2006 After tt STIR

Before tt STIR

Sequences: How to choose?

• T1 Gado FS –  Injection –  Inflammatory tract white –  Fibrosis/Fluid black – May overinterpret a healing

fistula

T1 Gado FS

STIR vs T1 Gado FS

•  STIR versus T1 Gado FS –  Overinterpretation of enhancement

with gado, while no fluid on STIR, when a fistula is on its way to heal

STIR

Gado FS

B 0

STIR vs T1 Gado FS Differentiate granulation tissue from fluid Before anti TNF treatment

Abscess? Granulation tissue? No abscess

Gado FS STIR

STIR vs T1 Gado FS

Abscess

STIR Gado FS

Sequences: How to choose?

• Combined T1 Gado FS + STIR • Role of DW MRI?

Axial STIR T1 gado FS Axial diff b500

T2 Fusion diff-T2

Fusion diff-T2 Ax T1 Gado FS

MRI Technique

• Slice thickness –  3-4 mm

• Section Planes –  Axial - relationship to sphincters –  Coronal - level of internal opening and relationship to levator ani muscles.

–  Sagittal may be useful (anovaginal fistula)

MRI Technique- Slice positioning Important to assess the level of internal opening with regard to puborectal muscle and better evaluation of relationship/ levator ani

MRI Technique • FOV – not just anal canal

–  In some cases must cover perineum, presacral space, supralevatorian space

Anatomy

External Sphincter-T2 •  Prolongs puborectal muscle •  Striated muscle •  Circular •  Hyposignal

2 cm

Anatomy

Internal Sphincter- T2/STIR •  Prolongs rectal muscular layer •  Smooth muscle •  Circular •  Intermediate to high signal

GADO FS

Classification •  Why is it important?

ü Aims of surgery o  Continence

preservation o  Infectious foci and

secondary tracts elimination

ü Surgical Options o  Seton tight or not o  Fistulotomy-

Fistulectomy o  Intersphincteric

amputation, Flap

Pr Halligan

o  Fistulotomy-Fistulectomy

Intersphincteric amputation

Superficial Fistula Horsthuis AJR 2004

T2

Intersphincteric Fistula Involvement of internal sphincter No risk for continence Horsthuis AJR 2004

Transphincteric Fistula Involvement of both internal and external sphincters External sphicter section threatens continence

Ax gado FS

Transphincteric Fistula •  Sometimes internal opening less obvious but predictable,

located at the penetrating point of the external sphincter or at the epicenter of the intersphincteric sepsis.

Suprasphincteric Fistula 20 % Rare, upwards and crosses the levator ani muscle.

Its section may threaten continence. Often inaccurately classified

Extrasphincteric Fistula= primitive rectal disease (CD, cancer, diverticulitis)

Ax Gado FS

Complications

• Abscess

Complications

Dr Damian Tolan, Leeds

Report 1.Fistula type - simple, complex, anovaginal, horseshoe

Ax T2 fusion

Ax gado FS

Coro gado FS

1.Fistula Type 2. Internal opening

Level and position (clockwise)

Report

1.Fistula type 2. Internal opening Level and position (clockwise) 3. Primary fistula pathway to the external opening Location and hour

Report

1.Fistula type 2. Internal opening Level and position (clockwise) 3. Primary fistula pathway to the external opening Location and hour

Report

1.Fistula type 2. Internal opening Level and position (clockwise) 3. Primary fistula pathway to the external opening Location and hour 4. Number and position of supralevatorian extensions?

Report

1.Fistula type 2. Internal opening Level and position (clockwise) 3. Primary fistula pathway to the external opening Location and hour 4. Number and position of supralevatorian extensions?

5. Number and positions of collections

Report

Report

• Activity Criteria – Hypersignal T2 – Enhancement

T2 Stir

Ax gado FS

B1000

B0

Report

• Sphincter • Rectum

T1 FS Gado

•  Main anatomic criteria –  Fistula type

•  Simple •  Complex •  Horseshoe •  Ano-vaginal

–  Relationship with levator ani muscle

–  Parks’classification

•  Intersphincteric •  Transsphincteric •  Suprasphincteric •  Extrasphincteric

–  Openings

•  Others –  Presence of a seton –  Distant extension –  Sphincteric ring

abnormalities (rupture…)

•  Inflammation criteria –  Fistula

•  Hypersignal T2 •  Enhancemnet

–  Abscess –  Rectal wall