Download - MRI imaging of Perianal fistula
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MRI IMAGING OF PERIANAL FISTULA
Dr. Ahmed Refaey , FRCR Consultant Radiologist Riyadh Military Hospital
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Format of the lecture
Anatomy Pathogenesis Imaging techniques Scanning protocoles Classification Examples
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ANATOMY
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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
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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
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Puborectal muscle has its origin on both sides of the symphysis pubis, forming a sling around the anorectum
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The puborectal muscle is contracted at rest and accounts for the 8O0 angulation of the anorectal junction . It relaxes during defecation
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On axial and coronal MR images , the different layers of anal sphincter and the surrounding structures can be displayed perfectly
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Axial Coronal
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PATHOGENESIS
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Perianal fistula
Abnormal connection between the epithilialised surface of the anal canal and the skin.
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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
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IMAGING TECHNIQUES
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Imaging techniques
Fistulography Endosonography CT MRI
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Perianal fistulography
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Anal endosonography
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CT
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MRI protocol
T1W &T2W fse axial and coronal T2W with fat sat T1W + CM FOV 200
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T2W ----- anatomy T2W with fat sat ---- fistula
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The anal clock
P: anterior perineum
n: natal cleft
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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
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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
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CLASSIFICATION
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Classification
Parks classification
1- intersphincteric 2- transsphincteric3- extrasphincterisc4-suprasphincteric
Intersphincteric & transsphincteric are the most commonIntersphincteric --> 70 %Transsphincteric -->20%
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MR imaging Grading of perianal fistulas
St. James university hospital classification
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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
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Grade 1 : simple linear intersphincteric fistula
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Intersphincteric fistula
Axial T2W with and without fat saturation
The intersphincteric fistula located at 6 o’clock
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Perianal fistula with an abscess
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Grade 2 :intersphincteric fistula with abscess or 2ry track
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Grade 3 :transspincteric fistula
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Transsphincteric fistula
The defect through internal & external sphincter at 6 o’clock is clearly visible
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Transsphincteric fistula at 11 o’clock
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Grade 4:transsphinteric fistula with abscess or2ry track within ischeorectal fossa
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Grade 5 :supralevator & translevator fistula
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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)
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Extrasphincteric fistula
A small abscess in left ischeoanal fossa , the fistula runs through levator ani , it is therefore above the sphincter complex and extrasphincteric
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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
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Differential diagnosis
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Pielonidal sinus
Small abscess just above the nates No relation with sphincter complex
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Proctitis
No fistula was seen Diffuse thickening of rectal mucosa due to
proctitis
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Ischiorectal space abscess
An abscess in ischiorectal space with no connection to the sphincter complex
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REFERENCES
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Goodsall DH, Miles WE. Diseases of the anus and rectum. London, England: Longmans, Green, 1900.
↵ Parks AG, Gordon PH, Hardcastle JD. A classification of fistula-in-ano. Br J Surg 1976; 63:1-12.
↵ Halligan S. Imaging fistula-in-ano. Clin Radiol 1998; 53:85-95.
↵ Kuijpers HC, Schulpen T. Fistulography for fistula-in-ano: is it useful? Dis Colon Rectum 1985; 28:103-104.
↵ Weisman RI, Orsay CP, Pearl RK, et al. The role of fistulography in fistula-in-ano: report of 5 cases. Dis Colon Rectum 1991; 34:181-184.
↵ Choen S, Burnett S, Bartram CI, Nicholls RJ. Comparison between anal endosonography and digital examination in the evaluation of anal fistulae. Br J Surg 1991; 78:445-447.
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↵ Guillaumin E, Jeffrey RB, Shea WJ, et al. Perirectal inflammatory disease: CT findings. Radiology 1986; 161:153-157.
↵ Yousem DM, Fishman EK, Jones B. Crohn disease: perirectal and perianal findings at CT. Radiology 1988; 167:331-334.
↵ Barker PG, Lunniss PJ, Armstrong P, Reznek RH, Cottam K, Phillips RK. Magnetic resonance imaging of fistula-in-ano: technique, interpretation, and accuracy. Clin Radiol 1994; 49:7-13.
↵ Spencer JA, Ward J, Beckingham IJ, Adams C, Ambrose NS. Dynamic contrast-enhanced MR imaging of perianal fistulas. AJR Am J Roentgenol 1996; 167:735-741.
↵ Haggett PJ, Moore NM, Shearman JD, Travis SPL, Jewell DP, Mortensen NJ. Pelvic and perianal complications of Crohn's disease: assessment using magnetic resonance imaging. Gut 1995; 36:407-410.
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Koelbel G, Schmeidl U, Majer MC, et al. Diagnosis of fistulae and sinus tracts in patients with Crohn's disease: value of MR imaging. AJR Am J Roentgenol 1989; 152:999-1003.
Myhr GE, Myrvold HE, Nilsen G, Thoresen JE, Rinck PA. Perianal fistulas: use of MR imaging for diagnosis. Radiology 1994; 191:545-549.
↵ Hussain SM, Stoker J, Schouten WR, Hop WCJ, Lameris JS. Fistula-in-ano: endoanal sonography versus endoanal MR imaging in classification. Radiology 1996; 200:475-481.
↵ Halligan S, Bartram CI. MR imaging of fistula-in-ano: are endoanal coils the gold standard? AJR Am J Roentgenol 1998; 171:407-412.
↵ 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;
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THANK YOU