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Dr. Ahmed Refaey , FRCR Consultant Radiologist Riyadh Military Hospital. MRI imaging of Perianal fistula. Format of the lecture. Anatomy Pathogenesis Imaging techniques Scanning protocoles Classification Examples. Anatomy . Anatomy . - PowerPoint PPT Presentation
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MRI IMAGING OF PERIANAL FISTULA
Dr. Ahmed Refaey , FRCR Consultant Radiologist Riyadh Military Hospital
Format of the lecture
Anatomy Pathogenesis Imaging techniques Scanning protocoles Classification Examples
ANATOMY
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
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
Puborectal muscle has its origin on both sides of the symphysis pubis, forming a sling around the anorectum
The puborectal muscle is contracted at rest and accounts for the 8O0 angulation of the anorectal junction . It relaxes during defecation
On axial and coronal MR images , the different layers of anal sphincter and the surrounding structures can be displayed perfectly
Axial Coronal
PATHOGENESIS
Perianal fistula
Abnormal connection between the epithilialised surface of the anal canal and the skin.
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
IMAGING TECHNIQUES
Imaging techniques
Fistulography Endosonography CT MRI
Perianal fistulography
Anal endosonography
CT
MRI protocol
T1W &T2W fse axial and coronal T2W with fat sat T1W + CM FOV 200
T2W ----- anatomy T2W with fat sat ---- fistula
The anal clock
P: anterior perineum
n: natal cleft
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
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
CLASSIFICATION
Classification
Parks classification
1- intersphincteric 2- transsphincteric3- extrasphincterisc4-suprasphincteric
Intersphincteric & transsphincteric are the most commonIntersphincteric --> 70 %Transsphincteric -->20%
MR imaging Grading of perianal fistulas
St. James university hospital classification
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
Grade 1 : simple linear intersphincteric fistula
Intersphincteric fistula
Axial T2W with and without fat saturation
The intersphincteric fistula located at 6 o’clock
Perianal fistula with an abscess
Grade 2 :intersphincteric fistula with abscess or 2ry track
Grade 3 :transspincteric fistula
Transsphincteric fistula
The defect through internal & external sphincter at 6 o’clock is clearly visible
Transsphincteric fistula at 11 o’clock
Grade 4:transsphinteric fistula with abscess or2ry track within ischeorectal fossa
Grade 5 :supralevator & translevator fistula
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)
Extrasphincteric fistula
A small abscess in left ischeoanal fossa , the fistula runs through levator ani , it is therefore above the sphincter complex and extrasphincteric
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
Differential diagnosis
Pielonidal sinus
Small abscess just above the nates No relation with sphincter complex
Proctitis
No fistula was seen Diffuse thickening of rectal mucosa due to
proctitis
Ischiorectal space abscess
An abscess in ischiorectal space with no connection to the sphincter complex
REFERENCES
Goodsall DH, Miles WE. Diseases of the anus and rectum. London, England: Longmans, Green, 1900.
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↵ 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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↵ 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.
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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