An anorectal fistula is an abnormal tunnel that forms between the inner lining of the anal canal and the skin near the anus, almost always as a consequence of an anal abscess that has drained or burst. Roughly a third of people who undergo surgical drainage for an anal abscess go on to develop a fistula, and once one forms, it rarely heals on its own. The condition causes persistent drainage, pain, and recurrent infection, and treatment nearly always requires some form of procedure. What makes fistula management genuinely difficult is the tension between two competing goals: getting rid of the tunnel for good and preserving the sphincter muscles that control bowel continence.
How a Fistula Develops
The anal canal contains small glands that sit between the two rings of sphincter muscle. When one of these glands gets blocked and infected, an abscess forms. The abscess fills with pus and typically tracks outward, either draining spontaneously through the skin or requiring surgical incision and drainage. In many cases, the infection clears and the wound heals normally. But in a substantial number of patients, the connection between the gland and the skin surface persists as a lined tract, and that tract is the fistula.
A large multicenter study following nearly 500 patients after abscess drainage found that about 34% developed a fistula over a median follow-up of roughly three years. Several factors substantially increased the odds. Having Crohn’s disease raised the risk nearly sixfold. A history of recurrent abscesses quadrupled it. Even the location of the original abscess mattered: those seated deep in the tissue between the sphincter muscles or in the fat-filled space beside the rectum were two to three times more likely to leave behind a fistula than superficial ones.1SpringerOpen. Fistula development after anal abscess drainage—a multicentre retrospective cohort study
Types of Fistula and Why Classification Matters
Surgeons classify fistulas by how much sphincter muscle the tunnel passes through, because that determines what can safely be done to fix it. The most widely used system describes four main types. Intersphincteric fistulas run in the space between the two sphincter muscles and are the most common, accounting for more than half of cases. Trans-sphincteric fistulas punch through the external sphincter and make up roughly 39%. Suprasphincteric and extrasphincteric fistulas, which travel above or entirely outside the sphincter complex, are uncommon but the most surgically challenging.2PubMed Central. Precise and comprehensive evaluation of perianal fistulas, classification and related complications using magnetic resonance imaging
Fistulas are also broadly divided into “simple” and “complex.” A simple fistula has a single tract, passes through a small amount of muscle, and has one external opening. A complex fistula may involve multiple tracts, horseshoe extensions that curve around the anus, a high location through thick sphincter muscle, or an association with Crohn’s disease. That simple-versus-complex distinction drives virtually every treatment decision.
Diagnosis and Imaging
A surgeon can often identify a fistula during a physical exam by seeing the external opening and feeling the cord-like tract under the skin. But the exam alone does not reliably reveal the full anatomy: where the internal opening sits, how much muscle is involved, whether hidden branches or abscesses exist. Missing those details is one of the main reasons fistula surgery fails, so imaging before an operation is increasingly standard.
The two main imaging tools are pelvic MRI and endoanal ultrasound (a small probe inserted into the anal canal). A review of the evidence found that both methods have acceptably high sensitivity for detecting fistula tracts, around 87%, but neither is great at ruling out disease when it is absent, with MRI showing better specificity at 69% compared to ultrasound at 43%.3PubMed. Perianal fistulas: A review with emphasis on preoperative imaging In practice, ultrasound tends to perform better for the more common low-lying fistulas and for pinpointing the internal opening, while MRI has the edge for complex, high, or branching tracts.4PubMed. Comparison of MRI and Endoanal Ultrasound in Assessing Intersphincteric, Transsphincteric, and Suprasphincteric Perianal Fistula Many centers use MRI as the default preoperative study, particularly when the fistula appears complex on examination.
Treating Simple Fistulas
For a straightforward fistula that involves only a small amount of sphincter muscle, the gold standard is a fistulotomy: the surgeon lays the tunnel open from end to end, converting it into a shallow groove that heals from the bottom up. It sounds dramatic, but the results are excellent. A systematic review pooling data from nearly 5,000 patients who underwent fistulotomy or a similar sphincter-cutting procedure found a weighted average healing rate of about 94%.5PubMed Central. Simple fistula-in-ano: is it all simple? A systematic review
The trade-off is continence. Cutting through even a small portion of the sphincter can leave some patients with difficulty controlling gas or, less commonly, stool. That same review found that about 13% of patients reported some degree of continence impairment after fistulotomy.6PubMed Central. Simple fistula-in-ano: is it all simple? A systematic review Most of these cases are mild, things like occasional urgency or minor leakage of gas rather than frank incontinence, and some improve over time. One study tracking patients after fistulectomy (removing the entire tract rather than laying it open) found an overall incontinence rate under 9% at 18 months, with the majority of affected patients experiencing only mild symptoms that responded to conservative measures like dietary fiber adjustments and pelvic floor exercises.7PubMed Central. Fistulectomy and incontinence: do we really need to worry?
Seton Procedures for Complex Fistulas
When a fistula passes through a significant chunk of sphincter muscle, laying it wide open would risk serious incontinence. The oldest and still most widely used alternative is a seton: a thread, rubber band, or silicone loop passed through the tunnel and tied in a loose ring. In its simplest form, a draining seton sits in the tract to keep it open and prevent new abscesses from forming, buying time while inflammation settles. A cutting seton, by contrast, is gradually tightened over weeks so that it slowly slices through the muscle, allowing tissue to scar and heal behind it rather than gaping open all at once.
One series of 128 patients treated with a “hybrid” seton for high fistulas found that the slow, controlled cutting approach helped maintain continence while achieving satisfactory healing, with significant improvement in quality-of-life scores.8PubMed Central. Hybrid seton for the treatment of high anal fistulas: results of 128 consecutive patients Modified versions of the cutting seton that try to spare the internal sphincter muscle have also been tested. A randomized trial comparing a conventional cutting seton to one that rerouted the thread through the space between the sphincters found no difference in healing time or recurrence, but the modified version showed consistently higher resting pressures on manometric testing, suggesting better preservation of the internal sphincter’s resting tone.9PubMed. Conventional cutting vs. internal anal sphincter-preserving seton for high trans-sphincteric fistula: a prospective randomized manometric and clinical trial For particularly high and complex fistulas, combining seton placement with a partial internal sphincterotomy has shown improved functional recovery and lower recurrence compared to seton alone.10PubMed Central. Combined Parks Seton placement and transanal sphincterotomy improves outcome and reduces recurrence in high-position complex anal fistula
Sphincter-Sparing Operations
Over the past two decades, several procedures have been developed specifically to cure fistulas without cutting through the sphincter at all. The appeal is obvious: no muscle division means essentially no risk of incontinence. The challenge is that healing rates are generally lower than fistulotomy, and recurrence is more common.
The LIFT procedure (ligation of the intersphincteric fistula tract) works by approaching the tunnel through the space between the two sphincters, tying off the tract and dividing it. A meta-analysis reported a mean success rate of about 76%, with zero incontinence and a postoperative complication rate of just over 5%.11PubMed. Ligation of intersphincteric fistula tract (LIFT) to treat anal fistula: systematic review and meta-analysis A separate systematic review found a similar healing rate of roughly 81%, with all patients remaining continent and fistula recurrence occurring in fewer than 8% of cases.12PubMed. Overview of anal fistula and systematic review of ligation of the intersphincteric fistula tract (LIFT) One smaller study found a less optimistic initial success rate of 40%, though further surgery brought the ultimate cure rate to 75%.13PubMed Central. Perianal fistulas and the lift procedure: results, predictive factors for success, and long-term results with subsequent treatment The wide range probably reflects differences in patient selection and fistula complexity across studies.
Advancement flap procedures take a different approach. The surgeon covers the internal opening of the fistula with a flap of tissue raised from the rectal wall, cutting off the source of ongoing infection. A long-term study following 81 patients found primary fistula closure in 43%, with 22% classified as true recurrences and the remainder persisting as unhealed tracts.14PubMed Central. Mid- and long-term functional outcomes of advancement flap for cryptoglandular perianal fistulas An older but instructive comparison found that using a full-thickness flap (including the muscle layer of the rectal wall) dramatically reduced recurrence compared to a partial-thickness flap: just 5% versus 35%.15PubMed. Endorectal advancement flaps in the treatment of high anal fistula of cryptoglandular origin: full-thickness vs. mucosal-rectum flaps Patients with multiple prior anal surgeries were at highest risk for failure with flap repair.
Video-Assisted and Minimally Invasive Approaches
Video-assisted anal fistula treatment, or VAAFT, uses a tiny endoscope inserted into the fistula tract itself. The surgeon can see the tract from inside, identify branches or hidden openings, and then destroy the lining of the tunnel using electrocautery or laser energy before closing the internal opening. A meta-analysis found that VAAFT was associated with a lower recurrence rate and fewer postoperative complications compared to conventional approaches for complex fistulas, along with better quality-of-life scores afterward.16BJS Open. Video-assisted anal fistula treatment for complex anorectal fistula: meta-analysis A separate systematic review concluded that VAAFT serves a dual role as both a diagnostic and therapeutic tool, offering satisfactory outcomes with acceptably low complication rates.17PubMed. A Systematic review and meta-analysis of the efficacy and safety of video-assisted anal fistula treatment (VAAFT)
Laser fistula closure is a related concept: a laser fiber is drawn through the tract, delivering energy that seals it from inside. Early reports have shown healing rates above 80% in small series.18PubMed Central. Video-assisted anal fistula treatment (VAAFT): a novel sphincter-saving procedure for treating complex anal fistulas These techniques are still evolving and not yet universally available, but they represent a genuine shift toward procedures that leave the sphincter entirely intact.
Biological Plugs, Fibrin Glue, and Stem Cells
The idea of sealing a fistula with a material rather than cutting anything has obvious appeal. Two biological options have been studied most extensively. Fibrin glue, injected to fill and seal the tract, has shown modest healing rates of about 39% in comparative studies. Biological fistula plugs, cone-shaped pieces of processed tissue inserted into the tract, have fared somewhat better at around 59%, performing comparably to advancement flaps and significantly outperforming both seton placement and fibrin glue for high trans-sphincteric fistulas.19PubMed. Anal fistula plug and fibrin glue versus conventional treatment in repair of complex anal fistulas A systematic review confirmed that plugs produced statistically better healing than fibrin glue.20PubMed Central. Fibrin glue in the treatment of anal fistula: a systematic review Neither approach carries meaningful continence risk, which is why they remain in the toolkit despite unspectacular cure rates. They can be worth trying first in complex cases, since failure does not burn any surgical bridges.
For patients with Crohn’s disease, the landscape shifted with the development of darvadstrocel, a therapy using stem cells derived from fat tissue. The landmark ADMIRE-CD trial demonstrated that darvadstrocel was superior to placebo for achieving both clinical and imaging-confirmed remission of complex perianal fistulas.21PubMed Central. Effectiveness and safety of darvadstrocel in patients with complex perianal fistulizing Crohn’s disease: a systematic review Long-term follow-up at two years showed clinical remission in roughly 50% to 59% of treated patients, regardless of whether they were also receiving anti-TNF biologic therapy.22PubMed Central. Follow-up Study to Evaluate the Long-term Safety and Efficacy of Darvadstrocel (Mesenchymal Stem Cell Treatment) In Patients With Perianal Fistulizing Crohn’s Disease: ADMIRE-CD Phase 3 Randomized Controlled Trial Those numbers may not sound overwhelming, but for a population in which long-term remission with conventional surgery tops out at about 50%, a non-surgical biologic option that matches or approaches that ceiling is meaningful.23PubMed Central. Treatment Strategy for Perianal Fistulas in Crohn Disease Patients: The Surgeon’s Point of View
Why Fistulas Come Back
Recurrence is the defining frustration of fistula surgery. A meta-analysis of risk factors identified several features that dramatically increase the chance of a fistula returning. The single strongest predictor was failure to identify the internal opening during surgery, which raised recurrence risk more than eightfold. High trans-sphincteric fistulas carried nearly five times the risk. Horseshoe extensions, multiple tracts, and prior anal surgery all independently increased the odds as well.24PubMed. Risk Factors for Recurrence after anal fistula surgery: A meta-analysis
A broader overview grouped recurrence risk into four categories: the inherent anatomy of the fistula itself and any associated conditions like Crohn’s disease; inadequate preoperative imaging that leaves branches or hidden openings undetected; intraoperative failures including wrong procedure selection, surgeon inexperience, and incomplete removal of the tract; and poor postoperative care.25PubMed Central. Factors Increasing the Risk of Recurrence in Fistula-in-ano The implication for patients is that getting good preoperative imaging and choosing a surgeon experienced specifically in fistula surgery are among the most controllable factors.
The Crohn’s Disease Connection
Perianal fistulas are among the most debilitating complications of Crohn’s disease. They tend to be more complex, more recurrent, and harder to treat than fistulas that arise from infected glands alone. Management in Crohn’s patients is almost always multidisciplinary, combining medical therapy (typically biologic drugs like infliximab) with surgical drainage and staged procedures. Even with this combined approach, long-term remission is reported to reach about 50% at best.26PubMed Central. Treatment Strategy for Perianal Fistulas in Crohn Disease Patients: The Surgeon’s Point of View The first surgical step is usually seton placement to control infection and drain any abscess, followed by definitive treatment once the bowel disease is medically optimized. Some patients ultimately require proctectomy, the removal of the rectum with creation of a permanent stoma, when the disease is refractory.
The emotional and social toll on Crohn’s patients with perianal fistulas is severe. Qualitative research found that the impact goes well beyond physical symptoms, damaging intimate relationships, limiting social engagement, and causing losses in work and life opportunities. The burden of repeated treatments and unpredictable symptoms compounds an already difficult chronic illness.27PubMed Central. Burden of disease and adaptation to life in patients with Crohn’s perianal fistula: a qualitative exploration
Living With a Fistula and Quality of Life
Even for patients without Crohn’s, living with a fistula significantly erodes quality of life. Compared to population norms, patients with anal fistulas score lower across multiple quality-of-life domains. Those with recurrent disease or urgency are hit hardest.28PubMed Central. Quality of life with anal fistula Interviews with patients describe a condition that requires significant readjustment to daily life, with impacts on psychological and social wellbeing that extend far beyond the physical symptoms of pain and drainage.29PubMed Central. Living with cryptoglandular anal fistula: a qualitative investigation of the patient’s experience through semi-structured patient interviews
For patients who do develop continence issues after surgery, pelvic floor physiotherapy and biofeedback training can help. These approaches aim to strengthen and coordinate the pelvic floor muscles, and colorectal rehabilitation literature supports their role in recovering function after anorectal procedures.30Journal of Coloproctology. Fecal incontinence as consequence of anorectal surgeries and the physiotherapeutic approach This is worth knowing because many patients fear that any continence change after fistula surgery is permanent, when in reality mild impairment often improves with time and targeted rehabilitation.
Unusual Causes and Mimics
While the vast majority of anorectal fistulas arise from infected anal glands, a small percentage have other origins that are important to recognize. Tuberculosis can cause perianal fistulas that look identical to ordinary ones on examination, with the same symptoms of pain, discharge, and recurrent tracts. The clinical features are not distinct enough to distinguish them without biopsy, which is why tissue sampling matters in cases that do not behave as expected.31PubMed Central. Ano-perianal tuberculosis–solving a clinical dilemma In rare instances, a chronic non-healing fistula can harbor malignancy. A case report described a patient with both anal mucinous adenocarcinoma and tuberculosis presenting as a chronic fistula, underscoring why persistent or atypical fistulas warrant biopsy.32PubMed Central. Synchronous anal mucinous adenocarcinoma and anal tuberculosis presenting as chronic anal fistula: Challenging management
Fistulas in Infants
Perianal abscesses and fistulas in infants are a different entity from the adult version. They occur overwhelmingly in boys, typically in the first year of life, and are thought to arise from immature anal glands influenced by circulating maternal hormones. A real-world study of over 150 infants found that more than 90% were cured with conservative management alone, without any surgery. Only about 7% ultimately required an operation, and just 2% went on to develop a true fistula.33Scientific Reports. Natural course of perianal abscess in infants: a real-world study The condition appears to be largely self-limiting as the hormonal influence wanes and the anal glands mature. Conservative treatment with warm baths, gentle hygiene, and observation is therefore considered the first-line approach, with surgery reserved for cases that truly fail to resolve.34PubMed Central. Conservative versus operative management of perianal abscess and fistula-in-ano in infants: a narrative review Parents who hear “fistula” in a pediatric context should know that the outlook is far more favorable than it is for adults.