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Background
Abbreviated MRI (AMRI) applications have been growing tremendously to improve the workflow. AMRI reduces redundancy by obtaining faster and essential sequences. Our proposed AMRI protocol for perianal fistula evaluation includes three key sequences: T2 HASTE, Axial T2 Fat Sat (T2FS); and axial T1 VIBE. DWI can be considered as optional pulse sequence as an alternative to contrast enhanced T1-weighted images (T1WI), especially for patients with allergies or risk factors for IV contrast agents. High-resolution thin slice 3D T2-weighted sequences (T2WI) generates volumetric dataset and can be considered as an optional sequence instead of nonfat-saturated 2D T2WI in multiple separate planes.

Educational Goals / Teaching Points
1) Discuss the AMRI protocol for perianal fistula evaluation. 2) Grading and management of fistulas.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
St. James University Hospital MRI classification of perianal fistula relies on the relationship of the fistula to the sphincter complex, location of the internal and external openings, secondary tracts, abscesses, and assessing the involvement of the Levator Ani are important in proper evaluation. The AMRI protocol for perianal fistula evaluation consists of T2 HASTE for evaluation of the anatomy, fat planes, and the fistula tract. T2FS helps to assess edema and fluid-containing tracts and cavities, whereas T1 VIBE is used to assess the abscesses, enhancing tracts, fibrosis, and granulation tissue, as well as inflammatory changes. Active fistula appears hypointense on T1WI and hyperintense on T2WI and shows contrast enhancement. Inactive tracts are hypointense on T1WI but are not hyperintense on T2WI and show variable contrast enhancement depending on the fibrosis and granulation tissue. Surrounding edema or inflammation is hyperintense on T2WI. Postsurgical changes like fat packing (hyperintense on T1WI), surgical drains and setons (linear low signal on T1WI and T2WI) and gas foci (focal low signal intensity on T1WI and T2WI) can be assessed. MRI follow-up may be used to guide management decisions as loss of hyperintense signal on T2WI precedes lack of enhancement, which correlates with clinical response.

Conclusion
AMRI protocol without compromising the diagnostic information is essential to improve the MRI workflow and will be a simpler, faster, and low-cost alternative to full perianal fistula protocol. Effective management of perianal fistulas needs precise radiologic information about the location, grading of the fistulous track, and the affected pelvic structures.