Your surgeon used a word you've never heard before. Maybe it was "intersphincteric" or "transsphincteric." Maybe they said "complex" and moved on before you could ask what that meant.

Here's what it all actually means.

Important: This content reflects personal experience and community-sourced tips, not medical advice. Every fistula case is different. Always discuss treatment decisions with your colorectal surgeon or gastroenterologist. What worked for one person may not be right for your situation.

Start here: what a fistula actually is

A fistula is an abnormal tunnel connecting two places that shouldn't be connected. An anorectal fistula runs from inside the anal canal to an opening on the skin outside.

Most fistulas start with an infection in a small gland just inside the anal canal. The infection forms an abscess. When that abscess drains, it sometimes leaves a tract behind. That tract is the fistula.

The type of fistula you have is defined by where that tract runs, specifically which muscles it passes through or around on its way out.

The one piece of anatomy worth knowing

There are two sphincter muscles that control the anal opening: the internal sphincter and the external sphincter. They sit one inside the other, like rings.

The internal sphincter is the inner ring. You don't control it consciously. The external sphincter is the outer ring. That's the one you can voluntarily squeeze.

Fistula classification is almost entirely about how the tract relates to these two muscles. That's it. Once you understand that, the names start to make sense.

The four main types

Intersphincteric

The most common type. The tract runs between the two sphincter muscles and exits through the skin close to the anal opening.

Because the tract passes between the muscles rather than through them, this type is generally considered lower complexity. The external sphincter is not involved, which matters a lot when it comes to surgical risk.

If your surgeon described your fistula as "simple" or "straightforward," this is likely what they meant.

Transsphincteric

The tract passes through both sphincter muscles before exiting through the skin, usually further out than an intersphincteric tract.

This type is more common than most people realize and covers a wide range. A low transsphincteric fistula passes through the lower portion of the external sphincter. A high transsphincteric fistula passes through more of it. That distinction matters because the more sphincter muscle involved, the more carefully the surgical approach needs to be planned.

This is the type where you're most likely to hear the word "seton."

Suprasphincteric

The tract goes up and over the top of the external sphincter before coming back down and exiting through the skin. It essentially loops over the muscle rather than through it.

Less common than the first two. Still manageable, but the path the tract takes makes it more complicated to treat.

Extrasphincteric

The rarest type. The tract runs from high inside the rectum all the way through to the skin, bypassing the sphincter complex entirely.

This type is uncommon and often has a specific cause, such as Crohn's disease, trauma, or a prior surgical complication. If this is your diagnosis, you're most likely already seeing a colorectal specialist.

What "complex" actually means

You may have heard your fistula described as simple or complex. These aren't official medical classifications but they're commonly used, and understanding them helps.

A simple fistula typically means it's low, has a single tract, and doesn't involve much sphincter muscle.

A complex fistula is a broader category. It can mean the tract is high, that it branches into multiple tracts, that it's associated with Crohn's disease or IBD, or that a previous surgery in the area complicates things. Horseshoe fistulas, which branch in both directions around the anal canal, fall into this category.

Complex doesn't mean untreatable. It means the approach requires more planning and often more than one procedure.

The question worth asking your surgeon

Most surgeons will tell you the type of fistula you have. Not all of them will volunteer the detail you actually need, which is how much sphincter muscle is involved.

That's the number that drives treatment decisions and recovery expectations more than the classification label itself.

A reasonable question to ask: "How much of the sphincter muscle does my tract involve, and how does that affect the options?"

You deserve a real answer, not a brush-off.

What's next

Now that you know what type you have, the next step is understanding what treatment looks like. The 5 Things I Wish I'd Known Before My Fistulotomy article covers what the pre-surgery reality looks like for fistulotomy patients. If a seton was mentioned, Living with a Seton: The Long Game is worth reading before your next appointment.