MRI of Recurrent Fistula-in-Ano: Is it Different from Treatment-Naïve Fistula-in-Ano and How Does it Correlate with Anal Sphincter Morphology?

Abstract

Abstract Objectives The main aim of this study was to compare magnetic resonance imaging (MRI) findings of recurrent and treatment-naïve fistula-in-ano and to correlate imaging findings with anal sphincter morphology in recurrent fistula-in-ano. Methods This is a retrospective study of adult patients who underwent MRI for suspected fistula-in-ano in 2018. After excluding patients with alternative diagnosis, patients were stratified into recurrent (n = 103) and treatment-naïve (n = 106) fistula-in-ano groups. Two blinded radiologists reread MRI scans in consensus for fistula characteristics and anal sphincter morphology. We compared imaging features of recurrent and treatment-naïve fistula-in-ano, assessed the incidence of anal sphincter scarring among patients with recurrent fistula-in-ano, and studied its association with fistula features. Results Two-hundred nine patients (187 males) with mean age of 40.6 (standard deviation: 12.2) years were included. Trans-sphincteric, inter-sphincteric, extra-sphincteric, and supra-sphincteric fistula-in-ano were seen in 63.6, 33, 2.9, and 0.5%, respectively. There were secondary tracts, supralevator extension, and secondary cause for fistula in 49.3, 12.9, and 14.8%, respectively. There was no difference between the fistula features of recurrent and treatment-naïve fistula-in-ano, except for significantly fewer external openings among recurrent fistula-in-ano (p = 0.005). Among patients with recurrent fistula-in-ano, MRI detected anal sphincter defect/scarring was seen in 53.4% (n = 55) and was significantly associated with posterior fistula-in-ano (p = 0.031), collections and/or supralevator extension (p = 0.010), and secondary tracts (p = 0.015). Conclusion Fistula features of recurrent and treatment-naïve patients were mostly similar. There was high incidence (53.4%) of MRI-identified anal sphincter scarring/defect among recurrent fistula-in-ano, which was significantly associated with posterior fistula, collections, supra or translevator extension, and secondary tracts. Key Points MRI-identified anal sphincter scarring is very common among patients with recurrent fistula-in-ano and seen in more than half of them. There was significantly higher incidence of sphincter scarring among patients who had posterior fistula, collections, supralevator/translevator extension, and secondary tracts.

Keywords

• fistula-in-ano
• mri
• recurrent
• anal sphincter
• incontinence