Why Do Anal Fistulas Recur? Causes and Next Steps

Anal fistulas can be incredibly frustrating, especially when they return after surgery. An anal fistula is a small tunnel that connects an infected gland inside the anus to an opening on the skin around the anus. When they recur, it is usually because a part of the fistula tract was left behind, the underlying cause of the fistula has not been fully addressed, or the surgical wound healed improperly ^[1][2]. Understanding why fistulas come back is the first step in working with your care team to find a lasting solution.

Hidden Tracts and Complex Anatomy

The most common reason an anal fistula returns is that its structure was more complex than initially thought ^[1]. While some fistulas are simple, straight tunnels, others have secondary tracks or branches that shoot off in different directions ^[1]. Some may even wrap around the anal muscles in a horseshoe fistula shape or extend high up into the pelvis (supralevator extension) ^[1].

If a surgeon operates without knowing about these hidden branches, a portion of the infected tunnel may be left behind. This remaining infection can eventually flare up and create a new opening, causing the fistula to recur.

The Role of Pelvic MRIs

Because complex fistula branches are often impossible to feel or see during a standard physical exam, imaging is crucial. A preoperative pelvic MRI (Magnetic Resonance Imaging) is considered a critical tool for mapping out the exact anatomy of your fistula ^[3][4][5]. High-resolution MRI scans allow surgeons to identify hidden tracts, branches, and abscesses before they even enter the operating room ^[3][4][6]. This detailed “road map” significantly improves surgical planning and helps ensure that no part of the infected tract is missed, which lowers the risk of the fistula coming back.

The Trade-off: Sphincter-Sparing Surgery

The type of surgery you undergo can also influence whether the fistula returns. For complex fistulas that pass through a large portion of the anal sphincter muscles, surgeons often choose sphincter-sparing procedures (such as the LIFT or TROPIS techniques) ^[7][8].

These procedures aim to treat the fistula while preserving your bowel control. Because the surgeon avoids cutting the muscle to protect against incontinence, these techniques can sometimes carry a slightly higher risk of recurrence compared to a traditional fistulotomy (where the tract is simply cut open) ^[7]. It is often a necessary and calculated trade-off to ensure your long-term quality of life.

Underlying Health Conditions

Your overall health and any underlying conditions play a major role in how well your body heals after surgery.

• Crohn’s Disease: Crohn’s disease is a type of inflammatory bowel disease that causes chronic inflammation in the digestive tract. Patients with Crohn’s are at a higher risk of developing anal fistulas, and these fistulas are notoriously difficult to treat and more likely to recur ^[2][9]. If Crohn’s disease is driving the fistula, managing the underlying inflammation with medication is essential. Surgery alone often isn’t enough, as the ongoing disease will continue to cause new fistulas.
• Smoking: Smoking restricts blood flow and impairs your body’s ability to heal wounds. Research shows that smoking is a significant risk factor that negatively impacts healing after fistula surgery, increasing the chances of recurrence ^[10]. Quitting smoking before and after surgery can improve your chances of a successful recovery.
• Diabetes and Obesity: Poor blood sugar control and higher body mass can also make it harder for surgical wounds to heal properly, increasing the risk of poorer surgical outcomes and recurrence ^[11].

Healing From the Outside In

Proper wound healing is just as important as the surgery itself. After an anal fistula is treated, the wound must heal from the inside out.

Sometimes, the skin on the outside of the wound heals too quickly, closing over the surgical site before the deeper tissues have finished healing. This is known as premature bridging. When the skin closes too soon, it traps fluid and bacteria inside, which can lead to a new abscess (a painful pocket of pus and infection), causing the fistula to return.

To prevent this, surgeons and wound care nurses may instruct you on specific ways to clean and pack the wound to ensure it stays open while the inside heals. In some cases, surgeons use a technique called marsupialization, where they stitch the edges of the wound open to promote faster healing and prevent the skin from closing too early ^[8][12].

While the idea of an open wound in a sensitive area can sound intimidating, your care team will provide detailed guidance on pain management and daily comfort measures. Techniques like warm water sitz baths, using a bidet instead of toilet paper, and taking prescribed stool softeners make daily wound care manageable and help ensure the area heals properly from the inside out.