الفهرس 
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Abstract
Anal fistula is defined as an abnormal connection between the epithelial lining of the anal canal and the skin over the perineum. Anal canal is a muscular tube surrounded by the internal and external anal sphincters with a space in between. The anal fistula causes signifi¬cant morbidity. The main presentation of the anal fistula is discharge from external opening. Surgery is considered as the cornerstone for the treatment of fistulas and success¬ful management needs distinct preoperative assessment of the course of the primary fistulous track and the site of any secondary extension or abscesses.
The fistula is classified according to the route taken by its primary tract (tract between internal and external openings). Initial classification of anal fistula was based on surgical anatomy described by Parks et al. then it was modified on the basis of anatomy on pelvic MRI which is known as the St. James’ University Hospital.
Fistulography is one of the most common methods that is used broadly but it has major drawbacks like difficult assessment of second¬ary tracts and inability to visualize anal sphincters. MRI is considered as the most descriptive imaging modality for anal fistula compared to other imaging modalities for two main reasons; it allows identification of infected tracks and ab¬scesses, also it makes the radiologist able to provide anatomical details about the anal sphincter complex.
Our study is a prospective study carried out in the period from March to November 2014. The study included twenty five patients (17 males and 8 females). All patients included in the study were diagnosed clinically and referred to radiology department for MRI examination of the anal region using the body coil.
The most appropriate protocol used in our institution for evaluation of anal fistula consists of the following sequences: oblique axial and oblique coronal T1-weighted FSE, oblique axial and oblique coronal T2-weighted FSE, oblique axial and oblique coronal STIR oriented perpendicular or paral¬lel to the long axis of the anal canal.
In our study we found that the intersphincteric and transsphincteric fistulas are the most common types representing 52% and 40% respectively. In our study we found that 76% of our patient had Low fistula form (below dentate line) and 24 % are high fistula (above dentate line); 33.3% of them were above the level of anorectal ring. In our study we found that the most common locations of the internal opening of the anal fistula in our patients according to anal clock in MRI axial images were at 6, 12 and 1 o’clock forming about 36%, 16% &12% respectively. In our study we found that 44% of the anal fistula in the studied patients was complicated by abscess and 12% of them had a horseshoe component.