Precise and comprehensive evaluation of perianal fistulas, classification and related complications using magnetic resonance imaging

Abstract

Objective: This study aimed to comprehensively evaluate perianal fistulas and their related complications using magnetic resonance imaging (MRI).

Methods: We enrolled 115 eligible patients who underwent preoperative perianal MRI. Primary fistulas, internal and external openings, and related complications were evaluated using MRI. All fistulas were classified according to Park's classification, Standard Practice Task Force classification, St. James's grade, and the position of the internal opening.

Results: In total, 169 primary fistulas were detected in 115 patients; 73 (63.5%) patients had a single primary tract and 42 (36.5%) patients had multiple primary tracts, and 198 internal and 129 external openings were identified. Based on Park's classification, 150 (88.7%) primary fistulas were classified into the following types: intersphincteric (82, 54.7%), trans-sphincteric (58, 38.6%), suprasphincteric (8, 5.3%), extrasphincteric (1, 0.7%), and diffuse intersphincteric with trans-sphincteric (1, 0.7%) types. Based on St. James's grade, 149 fistulas were classified into grade 1 (52, 34.9%), grade 2 (30, 20.1%), grade 3 (20, 13.4%), grade 4 (38, 25.5%), and grade 5 (9, 6.1%). We detected 92 (54.4%) simple and 77 (45.6%) complex perianal fistulas and 72 (42.6%) high and 97 (57.4%) low perianal fistulas. Furthermore, we detected 32 secondary tracts in 23 (20.0%) patients and 87 abscesses in 60 (52.2%) patients. Levator ani muscle involvement and extensive soft tissue edema were detected in 12 (10.4%) and 24 (20.9%) patients, respectively.

Conclusion: MRI is a valuable and comprehensive tool that can not only be used to determine the general condition of perianal fistulas but also to classify them and identify related complications.

Keywords: Perianal fistula; classification; complications; magnetic resonance imaging.

Figure 1

58-years old female patient with perianal fistula, intermittent secretion outflow for 1 year. Oblique axial FS T2WI (A) shows an internal opening at 6 o’clock (yellow arrow). Oblique coronal FS T2WI (B) shows fistula (orange arrow) and external opening (red arrow). FS T2WI: fat suppression T2 weighted imaging.

Figure 3

38-years old male patient with perianal fistula. Oblique axial FS T2WIs (A, B) show internal openings at 2 o’clock, 3 o’clock, 8 o’clock and 12 o’clock respectivly (yellow arrow). Oblique axial FS T2WIs (C, D) show multiple external openings on bilateral buttocks and right perineum (red arrow). Oblique coronal FS T2WIs (E-G) and oblique coronal T2WI (H) show bilateral intersphincteric and left transsphincteric anal fistula (orange arrow). Sagittal FS T2WIs (I-K) show primary fistula (orange arrow) and secondary fistula (green arrow). Oblique axial FS T2WI (L) shows associated abscess in left ischioanal space (blue arrow). FS T2WI: fat suppression T2 weighted imaging.

Figure 4

A 22-year old male patient with perianal fistula and abscess. Oblique axial FS T2WI (A) shows internal opening at 6 o’clock (yellow arrow). Oblique axial FS T2WI (A) and oblique coronal T2WI (C) show horseshoe abscess formation in intersphincter space (blue arrow). Oblique axial FS T2WI (B) shows extensive soft tissue edema in subcutaneous space of both buttocks (red arrow). Oblique coronal FS T2WI (D) shows inflammatory involvement of levator ani muscle (orange arrow). FS T2WI: fat suppression T2 weighted imaging.

Figure 2

A cohort of perianal fistula cases, which was classified according to Park’s classification. Oblique coronal FS T2WIs (A-C) show the fistula passes through the external sphincter, which is a trans-sphincteric perianal fistula (orange arrow). Oblique coronal FS T2WI (D) shows a intersphincteric perianal fistula (orange arrow). Oblique coronal FS T2WI (E) shows a suprasphincteric perianal fistula (orange arrow). Sagittal FS T2WI (F) shows a extrasphincteric perianal fistula (orange arrow). * shows internal sphincter; # shows external sphincter. FS T2WI: fat suppression T2 weighted imaging.