I had a fistula similar to yours (perianal area is where it came out), and it was terrible--got infected and became an abscess. (I have Crohn's disease as well).
Are you on Remicade? I went on Remicade shortly after getting this fistula, because Remicade is highly recommended for people with fistulizing Crohn's as it has been shown to aid in healing them.
After being on Remicade only 3 months, my fistula healed shut, and has not recurred (nor have I gotten any new ones) ever since being on this drug. Perhaps talk to your GI about
starting Remicade--if you have fistulas, your Crohn's is likely severe and Remicade should be an option for you. I love the drug, been on it 8 years + with no side effects or allergic reactions (I am 26, female, Crohn's since age 15).
Fistulas and abscesses are horrible.