Name : Morteza
Family : Sanei Taheri
Affiliation :Radiology Department,Shohada Tajrish Hospital,SBMU
Academic Degree : Associate Professor of Radiology
Resident : Afarin Sadeghian
Urology&Genital Male Imaging
Gender : Female
Age : 62
62-year-old woman with perianal discharge
The first two images(Fig.1,2),STIR sequences,show high signal fistulous tract next to the external sphincter which passes from ischioanal fossa to the skin opening.The gradient-echo T2-weighted with fat suppression image(Fig.3) demonstrates small focus of collection.Enhancement and also site of opening in 9 o'clock of anal canal are best seen on cotrast-enhanced axial and sagittal gradient-echo T1-weighted with fat suppression images(Fig.4-8).
1.Perianal fistula,2.Sinus pilonidalis,3.Abscess in the ischiorectal space
Active transsphincteric fistula with abscess formation(Grade 4)
Discussion (Related Text)
Knowledge of the anatomy of the anal sphincter complex and surrounding spaces is crucial for image interpretation (Fig.9). The anal canal extends from the levator ani muscle cranially to the anal verge caudally and is surrounded by the internal and external anal sphincters.The internal and external sphincters are separated by the intersphincteric space, which is composed of loose fat- containing areolar tissue. Surrounding the anal canal, superficial to the sphincter complex and inferior to the puborectalis, are two contiguous pyramidal fat-containing spaces known as the ischiorectal space cranially and the ischioanal space caudally.Once a fistula tract is detected, its relationship to the sphincter complex and location of the internal and external openings should be described by the radiologist interpreting the MRI examination. The internal opening can be described according to anterior-posterior and right-left locations or according to the “anal clock” with the patient in the supine position.Active fistula tract appears as a hypointense linear structure on T1-weighted imaging and hyperintense on T2-weighted imaging (best visualized with fat saturation) relative to muscle and enhances with IV contrast agent.Initial classification of perianal fistulas was based on surgical anatomy described by Parks et al. MRI classification of perianal fistula is divided as:Grade 1: Simple Linear Intersphincteric Fistula,Grade 2: Intersphincteric Fistula With Intersphincteric Abscess or Secondary Fistulous Tract.The “horse- shoe” fistula subtype has a secondary tract that crosses the midline and surrounds both sides of the internal sphincter,Grade 3: Transsphincteric Fistula,Grade 4: Transsphincteric Fistula With Abscess or Secondary Tract Within the Ischioanal or Ischiorectal Fossa,Grade 5: Supralevator and Translevator Disease(Fig.10),Others (Not Specifically Described in the Parks Classification) :Submucosal fistulas are superficial tracts that arise inferiorly from the anal canal and extend to the skin surface without involving the internal or external anal sphincters. Superficial tracts without an internal opening or communication with the anal canal are classified as sinus tracts.
1.AJR 2012; 199:W43–W53,2.RadioGraphics,2000,Vol.20:623-635