Idol, I had my fissure for five years too. I had a 'fistula freakout' at one point, after I had the LIS because I had a pimple-like thing develop on the outside. It turns out it was just a pimple... :) The main thing to look for with a fistula would be discharge of pus, usually coming from what looks like a pimple near the anus, but I guess not necessarily if the fistula hasn't formed a tract leading to the outside yet. It almost never goes away without surgery. I really think there would be a noticeable discharge though. Granted I'm no fistula expert because I never had one. You may get better info from some of the threads written by people with actual fistulas!
I'm also not sure how far up inside a fissure can extend, but it's definitely true that they can be internal. How are you treating it? Are you taking any Miralax? Do you have a lot of bleeding? For me, Miralax was better for pain relief and stopping the bleeding than any ointment. It even took away the spasm pain I would get after the BM, but after five years of on/off pain with fissures, my poor rear had gotten so tight there was no help for it but LIS. Have you considered the surgery yet? One thing about it that's been a bit of a downer for me, is that it's taken a long time to heal from it. Not the incision itself; that healed fairly quickly, I just mean that I had several episodes of retears and bleeding that would occur every 4-6 weeks or so after I had the surgery. But just in the last couple of months things have gotten better (I had the surgery March 23 of last year). Now I feel like either the sphincter is stretching more easily or the skin has gotten stronger there or both. The last time I retore happened because I had a bout of stomach flu with horrible diarrhea followed by constipation. After that I started taking fish oil and evening primrose supplements and haven't had another retear, KOW.
I guess my point is that after 5 years, surgery is definitely worth it! 5 years is a long time and you're probably dealing with weak skin and scar tissue, so it may not be a quick fix for you, BUT I don't think it's anywhere near as risky as some doctors and some websites paint it to be. I'm not at all incontinent and I've had three babies. I hope you can find a permanent fix!