MRI features of perianal fistulas: is there a difference between Crohn’s and non-Crohn’s patients?

Abstract

Though perianal fistulas are commonly seen in patients with Crohn's disease, they can also be seen in patients without inflammatory bowel disease. The purpose of this study was to evaluate MR imaging differences of perianal fistulas in patients with and without Crohn's disease. Our retrospective search from January 2012 to December 2015 of the Radiology database for perianal fistula yielded 207 patients. Only patients with dedicated MR fistula protocol studies were included, whereas patients with previous anal surgery or anastomosis, anorectal tumors, and equivocal findings that could not be definitely assessed as a fistula were excluded. The following features were assessed: anatomic type of fistula (Parks Classification), luminal origin (hour clock position), anal verge distance, signs of acute inflammation, circumference of anus involved by inflammation, presence of rectal inflammation. and abscess. One hundred and twenty six of 207 patients met inclusion criteria. Of these, 96 (76.2%) had Crohn's disease and 30 (23.8%) did not. The most common fistulas identified were transphincteric (38.5% of Crohn's and 50% of non-Crohn's) and intersphincteric (33.3% of Crohn's and 35.4% of non-Crohn's). An abscess was associated in 41 cases, 32 (33.3%) in the Crohn's group and 9 (30.0%) in the non-Crohn's group. Rectal inflammation was present in 29 patients with Crohn's disease (29.2%) and in 2 without Crohn's (6.7%). This finding was statistically significant (p=0.0009). Our study demonstrates that while both groups can have similar MR imaging features, accompanying rectal inflammation was more commonly seen in Crohn's disease.