A fistula is an abnormal tunnel that forms between two body parts that shouldn’t be connected, such as two organs, or an organ and the skin. These passages are lined with inflammatory and healing tissue, which actually prevents them from closing on their own. Fistulas can develop almost anywhere in the body, but they most commonly affect the area around the anus, the intestines, the urinary tract, and the vagina.
How a Fistula Forms
Most fistulas start with an infection or inflammation that creates a pocket of pus (an abscess). When that abscess drains, either on its own or with medical help, the path it carves through tissue can persist as an open tunnel. The lining of this tunnel is made of the same type of cells your body uses to heal wounds, but because debris and fluid keep passing through, the tract stays open instead of sealing shut. Think of it like a hole that keeps getting irritated before it can close.
In the case of anal fistulas, the process typically begins when one of the tiny glands inside the anal canal gets blocked. Bacteria multiply in the blocked gland, an abscess forms in the surrounding tissue, and that abscess eventually drains to the skin near the anus, leaving a permanent channel behind. Even with surgical drainage of the abscess, there’s a significant risk that a fistula will develop afterward.
Common Causes
Infection and abscess formation are the most frequent triggers, but several other conditions can lead to fistulas:
- Crohn’s disease: Up to 50% of people with Crohn’s develop a fistula within 20 years of diagnosis. The chronic inflammation of the intestinal wall weakens tissue and creates openings between the bowel and nearby structures like the skin, bladder, or vagina. More than half of Crohn’s-related fistulas occur around the anus.
- Obstructed labor: Prolonged, difficult childbirth can compress the tissue between the baby’s head and the mother’s pelvic bones, cutting off blood supply and causing tissue death. This creates a connection between the vagina and the bladder or rectum, known as an obstetric fistula. An estimated 457,000 women worldwide live with this condition, overwhelmingly in regions with limited access to emergency obstetric care.
- Surgery or injury: Pelvic operations like cesarean sections or hysterectomies can accidentally damage tissue and create fistula tracts. Radiation therapy for cancers in the pelvis or abdomen is another known cause.
- Diverticular disease and cancer: Conditions that weaken or erode the intestinal wall can allow abnormal connections to form between the colon and surrounding organs.
Where Fistulas Develop
The location of a fistula determines its name and its symptoms. Anal fistulas, which connect the inside of the anal canal to the skin near the anus, are the most common type. About 70% of these run between the two rings of muscle that control the anus, making them relatively straightforward to treat. More complex types cross through or loop above these muscles, which makes surgery trickier because those muscles control bowel continence.
Fistulas can also connect the colon to the bladder (causing urinary tract infections and gas in the urine), the rectum to the vagina (causing stool or gas to pass through the vagina), or one section of intestine to another (causing diarrhea, pain, and weight loss because food bypasses part of the digestive tract). In people with Crohn’s disease, connections between loops of intestine account for 24 to 53% of fistulas.
Symptoms to Recognize
The hallmark symptom of an anal fistula is persistent drainage of pus from a small opening in the skin near the anus. This drainage may be bloody or foul-smelling, and it often stains underwear. Swelling and pain near the anus tend to come and go, sometimes accompanied by redness or fever when the tract becomes re-infected.
Fistulas in other locations produce different symptoms. A connection between the colon and bladder can cause gas or stool to appear in your urine, along with frequent urinary tract infections. A rectovaginal fistula causes gas or stool to pass through the vagina. Internal fistulas between segments of bowel may cause diarrhea, abdominal pain, and unexplained weight loss because nutrients aren’t being properly absorbed.
How Fistulas Are Diagnosed
A physical exam can often identify the external opening of an anal fistula, but mapping the full path of the tunnel requires imaging. MRI is the gold standard for evaluating fistulas, particularly around the anus and pelvis. It provides detailed images of the tract’s origin, its course through muscle and tissue, and any branching or abscesses that might complicate treatment. No special preparation is needed for the scan.
CT scans are useful for spotting abscesses but less reliable for tracing the fistula tract itself. Ultrasound performed through the anus can detect fistulas during surgery but has limited accuracy in a clinic setting. In some cases, a surgeon will examine the area under anesthesia to physically probe the tract and plan the repair.
Treatment Options
Most fistulas require some form of surgical treatment because they rarely heal on their own. The most common procedure for anal fistulas is a fistulotomy, where a surgeon cuts the entire tract open and lets it heal from the inside out as a flat wound. This approach has a success rate between 87% and 94%, making it highly effective for simpler fistulas.
For fistulas that pass through a significant amount of sphincter muscle, a fistulotomy would risk damaging bowel control. In these cases, surgeons use alternatives. A seton, which is a thin thread or rubber band looped through the tract, can be left in place for weeks or months to keep the tract open and draining while inflammation settles. Biologic plugs, made from material the body can absorb, can be inserted to seal the tract. In one study, fistula plugs successfully closed the tract in 87% of patients at three months, compared to 40% for fibrin glue, a liquid sealant injected into the tunnel.
People with Crohn’s disease often need a combination of medication to control intestinal inflammation alongside surgical management of the fistula itself. Treating the underlying disease is essential because the fistula will keep recurring if the inflammation driving it isn’t addressed.
Recovery After Surgery
After a fistulotomy, most people feel uncomfortable for the first few days but can return to normal daily activities within about two weeks. Complete wound healing, however, takes considerably longer. The open wound left by the procedure may need several months to fully close. During that time, you’ll likely need to keep the area clean with regular baths or showers and may use gauze pads to manage drainage.
Strenuous lower-body exercise, including deep squats and heavy lifting, is typically off-limits for the first few months. Your surgeon will guide you on when to resume specific activities based on how well the wound is healing.
What Happens Without Treatment
Leaving a fistula untreated allows the cycle of infection, abscess, and drainage to repeat indefinitely. Each recurrence can extend the tract, create new branches, or damage surrounding tissue. In rare but serious cases, uncontrolled infection around the anus can progress to Fournier’s gangrene, an aggressive, life-threatening infection of the skin and tissue in the genital and perineal area. Mortality rates for Fournier’s gangrene range from 15% to 50%, making prompt treatment of perianal abscesses and fistulas important.
Fistulas connecting the intestine to the bladder carry a persistent risk of urinary tract infections and kidney damage over time. Obstetric fistulas, when left unrepaired, cause continuous urinary or fecal incontinence that profoundly affects quality of life.
Surgically Created Fistulas for Dialysis
Not all fistulas are unwanted. For people with kidney failure who need long-term dialysis, surgeons intentionally create an arteriovenous (AV) fistula by connecting an artery to a vein, usually in the forearm. This causes the vein to enlarge and thicken over several weeks, creating a durable access point that can withstand repeated needle insertions during dialysis sessions. Compared to other types of dialysis access like plastic grafts or temporary catheters, AV fistulas have significantly lower rates of infection, hospitalization, and failure over time.