A fistula is actually a small channel that exits the anal canal to the outside. It can be related to a fissure, but most fissures don't develop a fistula.

yeah, val, don't get too alarmed.
i think your chances are higher if you don't keep your area clean. because when the fissure is active and open, then if you don't keep the area clean, fecal matter and other debris can get into the opening of the fissure.
at first, this can develop as an abscess if it keeps pocketing fecal matter and other bad stuff. without treatment, then all the bad stuff accumulates and has no where to go. because the bad stuff creates a biological chain of events, the molecules then start to erode and make a pathway deeper into the fissure and collects more bad stuff.
when this happens, bad stuff just gets pushed deeper and deeper, trying to find a way out..ie, making a tunnel, which then this has become a fistula. usually you can tell you have a fistula when you see the other exit opening around or outside of the anus. some people have fistulas that exit somewhere else on the buttcheek.
there are horseshoe fistulas which make a tunnel around your anus. that would be intense to treat as i think the would have to open the whole tunnel.
anyway, not all fissures lead to abscesses.
and not all fissures lead to fistulas.
just keep the area clean. and its always best to take a shower/bath after your BM to make sure you can cleanse the area well without irritating it with soaps and toilet paper or baby wipes.

"which came first, the fissure or the abcess then fistula?"
fissure=>abscess=>fistula

Often fistulas develop if the skin heals before the inside of the cut heals, thus trapping bm residue in the fissure. Those bacteria multiply and before you know it, you have an abscess or the tunneling abscess, mr fistula.

An update
Had surgery last Monday - 1 week later no Tylenol or other pain meds. Some discomfort, still don't like to sit. Not much pain with BM's or after. HATE IT when I have to go twice. Keeping my fingers crossed...

Some discomfort, still don't like to sit.
I don't know about your job, but do try *not* to sit as much as possible, even for another week or so. It will help a lot...

Just a 4 week surgery follow-up. No pain (nothing much past the first week). Mostly healed from the fistula surgery (some drainage, very slight discomfort). Fissue appears gone. Have moved onto occasional regular foods and have attend a few football games with no discomfort. Able to work sitting for 8-10 hours. Still keeping the fiber high and water content high and try to eat fruits and vegies but have the occasional slice of pizza or sub sandwich. Try to make sure my onter meals on those days are healthy. Still using Colase until the CRS says all is healed.
From start of Fissue till now about 3 months.

That is great news! I am so happy that you are doing much better and I think you are wise to keep up the routine even though you are close to being out of the woods!

Glad to hear things have gotten btter and you're getting out of the woods. Keep up the diet, and perhaps incorporate the fissure diet into your life permanently and maybe you'll never have to go through this again!

I realize this post is very old but there is some connection between fissure and abscesses I feel. The best way I can summarize is that the fissure somehow gets infected forming pus and this needs to escape somewhere. It isn't as uncommon as I initially thought. I would love to hear from people who have dealt with this and how and when they improved.