What Is an Abdominal Fistula? Causes and Treatment

An abdominal fistula is an abnormal tunnel-like connection that forms between an organ in the abdomen and another organ, body cavity, or the skin surface. The most commonly discussed type is the enterocutaneous fistula (ECF), which connects the intestine directly to the skin, allowing digestive contents to leak out through an opening in the abdominal wall. These are serious medical complications, most often arising after surgery, though diseases like Crohn’s and diverticulitis can also produce them. Treatment typically follows a stepwise approach: stabilize the patient, manage infections and nutrition, and then decide whether the fistula will heal on its own or require an operation.

What Counts as an Abdominal Fistula

The word “fistula” simply means an abnormal passage between two surfaces that shouldn’t be connected. In the abdomen, this can take many forms depending on which structures are involved. An enterocutaneous fistula runs from the bowel to the skin. An enteroenteric fistula connects one segment of bowel to another. A colovesical fistula links the colon to the bladder, causing urinary tract infections and sometimes air in the urine. A colovaginal fistula connects the colon to the vagina. Pancreatic fistulas leak digestive enzymes from the pancreas. The specific type matters because it determines the symptoms a person experiences, how dangerous the fistula is, and what treatment makes sense.

Fistulas are also classified by how much fluid drains through them. A high-output fistula produces more than 500 milliliters of fluid per day, while a low-output fistula produces less than 200 milliliters. This distinction drives a lot of the early management decisions, because high-output fistulas cause rapid dehydration, severe electrolyte problems, and skin breakdown around the opening.¹ Low-output fistulas, by contrast, are more likely to close on their own with conservative care.

Why Abdominal Fistulas Form

The overwhelming majority of enterocutaneous fistulas develop as a complication of abdominal surgery. In one large surgical series, about 84% of ECFs requiring operative repair had arisen after a previous operation, usually from a leaking surgical connection between two segments of bowel, an accidental injury to the intestine during surgery, or procedures complicated by dense scar tissue or prior radiation.² Patients who have had multiple prior abdominal operations, those undergoing emergency rather than planned surgery, and those with underlying inflammatory bowel disease are at higher risk.

Outside the surgical setting, Crohn’s disease is one of the most important causes. Crohn’s is a chronic inflammatory condition that can affect the full thickness of the bowel wall, and that deep inflammation creates the conditions for fistula formation. Researchers believe the process starts at a defect in the intestinal lining where chronic inflammation triggers cells to burrow deeper into the gut wall, causing tissue damage that eventually tunnels through to another organ or the skin surface. Inflammatory signaling molecules and enzymes that break down surrounding tissue appear to accelerate the process.³ The exact mechanisms are still being worked out, but immune system dysfunction and changes in gut bacteria also seem to play a role.⁴

Diverticular disease, one of the most common gastrointestinal conditions worldwide, is another frequent culprit. When infected or inflamed diverticula (small pouches in the colon wall) erode into adjacent structures, the result can be colovesical, colovaginal, or other fistula types. Diverticular fistulas account for a meaningful share of diverticular disease hospital admissions and often require surgery.⁵ Less common causes include abdominal cancers that erode through organ walls, radiation therapy to the pelvis or abdomen, abdominal abscesses, and certain infections.

Why These Fistulas Are Dangerous

An abdominal fistula is far more than an inconvenient wound. Mortality rates for enterocutaneous fistulas have been reported as high as 39% in some studies, though outcomes have improved substantially over the decades with better intensive care, antibiotics, and nutritional support.⁶ One institution documented a drop in in-hospital mortality from 44% in 1960 to about 3% in more recent years, illustrating just how much modern care has changed the outlook.⁷

The three main threats from an active fistula are sepsis, malnutrition, and fluid and electrolyte imbalance.⁸ Intestinal contents leaking into the abdominal cavity or pooling around the skin opening create a breeding ground for infection. Sepsis, where the body’s response to infection spirals out of control, is the leading cause of death in fistula patients. Malnutrition sets in because nutrients that should be absorbed in the intestine are instead lost through the fistula opening, and the ongoing inflammatory state increases the body’s calorie and protein needs at the same time. In high-output fistulas, fluid losses can be massive, pulling water and essential electrolytes like sodium and potassium out of the body faster than they can be replaced by mouth.⁹

The skin around the fistula opening also suffers. Digestive enzymes in the draining fluid break down surrounding skin, causing painful erosion that can become a source of secondary infection and make it difficult to attach wound care devices. Psychological distress is common too. Living with an abdominal fistula means coping with an uncontrolled drainage of intestinal fluid, often through the abdominal wall, which can be isolating and demoralizing.¹⁰

How Abdominal Fistulas Are Diagnosed

Doctors typically suspect a fistula based on the clinical picture: unexplained drainage from a surgical wound, bowel contents appearing where they shouldn’t, persistent abdominal infection that won’t resolve, or unusual symptoms like air or stool in the urine (suggesting a connection to the bladder). Confirming the diagnosis and mapping the fistula’s anatomy usually requires imaging.

CT scans and MRI are the primary tools. Both provide detailed cross-sectional pictures that reveal where the fistula runs, what organs it connects, whether there are associated abscesses or collections of fluid, and what underlying condition may have caused it.¹¹ MRI is particularly valuable for Crohn’s-related perianal fistulas because it shows soft tissue detail well without radiation. Ultrasound can also detect fistulas, abscesses, and narrowing of the bowel with good accuracy, though it is somewhat less reliable for abscesses specifically. A systematic review found that all three techniques had sensitivity and specificity above 80% for identifying fistulas and related complications.¹² In some cases, a traditional fistulogram — where contrast dye is injected into the fistula opening and X-rays are taken — is still useful to confirm the tract’s anatomy and whether it communicates with the bowel.

Conservative Treatment and Nutrition

Not every fistula needs surgery. A significant number close on their own with conservative management, particularly low-output fistulas and those without downstream obstruction, infection, or cancer at the site. The initial phase of treatment focuses on controlling sepsis with antibiotics and drainage of any abscesses, correcting dehydration and electrolyte disturbances, and starting nutritional support.

Nutrition is a central part of fistula care. The question of how to deliver it matters. A randomized trial comparing enteral nutrition (delivered through a tube into the gut) versus total parenteral nutrition (delivered intravenously) for pancreatic fistulas found that fistulas closed in 60% of patients fed enterally after 30 days, compared with 37% of those on intravenous nutrition. Low initial fistula output was the other major predictor of closure.¹³ The advantage of enteral feeding, when feasible, is that it maintains the health and function of the intestinal lining, which may support healing. Parenteral nutrition remains essential when the gut cannot be used safely, such as when the fistula sits in a location that would be worsened by food passing through.

Medications that reduce intestinal secretions can also help. Octreotide, a drug that suppresses the release of several digestive hormones, has been shown to cut fistula output substantially. In one study, octreotide reduced intestinal fistula output by an average of about 50% within 24 hours of starting treatment, and achieved a closure rate of 72% in intestinal fistulas after an average of 11 days.¹⁴ It is generally considered an add-on to standard care rather than a standalone treatment, but the reduction in fluid output alone makes patients more comfortable and easier to manage.¹⁵

Wound care around the fistula site is another critical element. Specialized wound nurses use skin barriers, adhesive pouches, and dressings to collect output, protect surrounding skin, and keep the patient dry. Negative-pressure wound therapy, which uses a sealed dressing connected to gentle suction, has gained traction as a way to manage fistula wounds. It helps contain drainage, promotes blood flow to the wound edges, and may serve as a bridge to definitive surgery or even help some fistulas close without an operation.¹⁶

Medical Therapy for Crohn’s-Related Fistulas

Fistulas caused by Crohn’s disease occupy their own treatment lane because the underlying problem is a chronic inflammatory condition that won’t resolve with surgical drainage alone. Biologic drugs that target tumor necrosis factor (TNF), a key driver of inflammation, have the strongest evidence base for fistula healing in Crohn’s disease. A network meta-analysis of randomized trials found that TNF-blocking drugs were significantly better than placebo at inducing both fistula response and remission.¹⁷

Even so, long-term healing with biologics alone is achieved in only about 30 to 50% of patients, which has pushed researchers to look beyond first-generation treatments.¹⁸ A recent systematic review and meta-analysis pooling data from randomized placebo-controlled trials found that several newer agents, including upadacitinib and ustekinumab, showed significantly higher rates of fistula remission compared with placebo. In the maintenance phase, infliximab and adalimumab helped sustain both fistula response and remission over periods of roughly six months to a year.¹⁹ The emerging picture is that combination strategies, where a biologic drug is paired with surgical drainage and close monitoring, tend to give the best results.

When Surgery Is Necessary

Surgery becomes necessary when a fistula fails to close with conservative measures, when there is a downstream bowel obstruction preventing healing, or when the underlying cause (such as a cancer or foreign body) cannot be resolved medically. The definitive operation typically involves cutting out the segment of bowel that contains the fistula and reconnecting healthy bowel on either side.²⁰

Timing is one of the most debated questions in fistula surgery. The traditional teaching has been to wait months after the fistula develops before operating, allowing inflammation to settle and the patient’s nutritional status to improve. A systematic review and meta-analysis confirmed that delaying surgery is associated with lower fistula recurrence rates.²¹ However, newer data suggests that early surgery may be feasible in selected patients. A retrospective study of 200 patients with postoperative ECFs found an overall surgical success rate of about 74%, and patients who had early surgery did not appear to have worse outcomes than those who waited.²² The decision about timing comes down to individual circumstances: how well the patient is doing nutritionally, whether infection is controlled, and how complex the anatomy has become.

Even with skilled surgery, complications are common. One study of patients undergoing surgical repair of small bowel fistulas reported that about 88% experienced at least one postoperative complication, though most were mild. Septic complications were the most frequent, accounting for roughly half of all complications. Patients whose fistulas recurred after surgery had all experienced at least one severe complication.²³ These numbers underscore why surgery is generally reserved for fistulas that won’t heal on their own and why patients need to be optimized beforehand.

Endoscopic and Stem Cell Approaches

For patients who are poor surgical candidates or who have fistulas in locations that are hard to reach operatively, endoscopic therapies offer a less invasive option. A range of devices deployable through an endoscope can be used to close fistula tracts, including clips, stents, suturing devices, sealants, and specialized plugs. These approaches have shown both safety and effectiveness, and they can sometimes spare patients a major abdominal operation.²⁴ They tend to work best for smaller fistulas with well-defined tracts, and combining multiple techniques often improves the odds of success.

Stem cell therapy is a newer and particularly promising avenue for Crohn’s-related perianal fistulas, which are notoriously difficult to heal with drugs or surgery alone. The approach involves injecting stem cells derived from fat tissue directly into and around the fistula tract, where they appear to dampen local inflammation and promote tissue repair. A phase II trial followed patients for two years after treatment with their own adipose-derived stem cells and found that complete healing was sustained in about 75 to 81% of patients, depending on how the analysis was conducted, with no safety concerns related to the cell therapy.²⁵ A commercially available product using donor-derived stem cells has also been studied in real-world settings and clinical trials, with encouraging results for long-term remission.²⁶ A systematic review concluded that adipose-derived stem cell therapy shows a favorable safety profile and meaningful symptom relief in a substantial proportion of patients, though outcomes vary and standardized treatment protocols are still needed.²⁷

The Financial and Practical Burden

Beyond the physical toll, abdominal fistulas impose a striking financial burden. A study of more than 288,000 emergency general surgery patients in 2016 found that those who developed an enterocutaneous fistula had median total hospital charges roughly three times higher than those who did not, with an extra cost attributable to the fistula of about $36,000 per patient.²⁸ In trauma patients, the gap was even wider: average hospital charges for fistula patients exceeded $539,000, compared to roughly $127,000 for trauma patients without a fistula, alongside dramatically longer ICU and hospital stays.²⁹

These numbers reflect the reality that fistula patients often spend weeks to months in the hospital, require multiple imaging studies, parenteral nutrition, wound care supplies, and frequently need readmission after discharge. Many need ongoing outpatient care from wound nurses, nutritionists, and surgeons even after the fistula has closed. For patients still living with an open fistula while waiting for definitive surgery, managing the drainage at home demands specialized supplies, regular follow-up appointments, and significant adjustments to daily life. The psychological impact of this prolonged, unpredictable illness is easy to underestimate, and access to mental health support and patient communities can make a meaningful difference during what is often a long recovery.