Evolution of anal fistula management: From traditional surgery to contemporary minimally invasive approaches

Objectives and methodology

This narrative review aims to critically analyse the current state of anal fistula management, with a specific focus on minimally invasive and sphincter-preserving techniques. We synthesised contemporary evidence to provide insights into optimal treatment selection, evaluate emerging innovations and identify future research priorities.

A comprehensive literature search was conducted across PubMed, Scopus and Web of Science databases covering publications from 2000 to 2025. Search terms included: ‘Anal fistula’, ‘fistula-in-ano’, ‘sphincter-preserving surgery’, ‘LIFT procedure’, ‘laser fistula treatment’, ‘stem cell therapy’, ‘minimally invasive’ and ‘treatment outcomes’. Inclusion criteria encompassed clinical trials, prospective cohort studies, systematic reviews and meta-analyses reporting surgical outcomes, functional results or quality of life measures. Studies with fewer than 10 patients, case reports without novel insights and non-English publications were excluded. Data extraction focused on success rates, complication profiles, functional outcomes and comparative effectiveness across treatment modalities.

Updated classification system

Modern classification systems stratify fistulas based on anatomical complexity, sphincter involvement and prognostic implications.^[8,9] The contemporary grading framework [Table 1] integrates traditional anatomical descriptions with functional considerations to guide treatment selection. Simple fistulas (Grade I-II) involve minimal sphincter muscle and demonstrate high success rates with conventional surgical approaches. Complex fistulas (Grade III-V) involve substantial sphincter musculature, multiple tracts or associated complications, requiring sphincter-preserving techniques to minimise functional morbidity.

Advanced imaging for treatment planning

High-resolution magnetic resonance imaging (MRI) combined with dynamic anal ultrasonography provides a comprehensive anatomical assessment essential for surgical planning.^[10,11] Three-dimensional endoanal ultrasound enables real-time intraoperative guidance, particularly valuable in complex revision cases.^[12] Diffusion-weighted MRI sequences differentiate active inflammation from fibrotic tissue, informing treatment timing and modality selection.^[13] Figure 1 demonstrates the multimodal imaging approach across different fistula grades, illustrating how advanced imaging techniques guide optimal treatment selection and surgical planning.

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Figure 1:

Multimodal imaging approach to anal fistula diagnosis and classification.

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Figure 1 multimodal imaging approach to anal fistula diagnosis and classification. The panel demonstrates various imaging modalities, including fistulography, ultrasound and MRI across different fistula grades. Case 1 shows fistulography technique, Case 2 demonstrates ultrasound findings and Cases 3–11 illustrate MRI appearances of different fistula classifications from simple intersphincteric (Grade 1) to complex suprasphincteric fistulas (Grade 5), with additional cases showing contrast enhancement and associated perianal abscesses.

Ligation of intersphincteric fistula tract (LIFT)

The LIFT procedure has emerged as a leading sphincter-preserving technique since its introduction, demonstrating success rates of 65–80% with minimal functional morbidity.^[14,15] The technique involves identification and ligation of the fistula tract within the intersphincteric space, preserving anal sphincter integrity. Contemporary modifications, including LIFT-plus (incorporating external tract core-out or biological plug insertion), report enhanced outcomes in selected cases.^[16]

Critical analysis of pooled data reveals several factors influencing LIFT success: Straight non-branching tracts demonstrate superior healing compared to complex anatomy, absence of active inflammation correlates with improved outcomes and primary procedures outperform revision cases.^[17] Pre-operative MRI assessment identifying excessive intersphincteric oedema or fibrosis predicts higher failure rates, suggesting the need for alternative approaches or staged treatment.^[18] Functional outcomes remain excellent, with incontinence rates under 5% in most series, substantially lower than traditional fistulotomy for comparable cases.

Endorectal advancement flaps

Advancement flap techniques achieve success rates of 70–85% in contemporary series while preserving anal function.^[19,20] The procedure involves mobilisation of healthy mucosa, submucosa and circular muscle to cover the internal opening after fistula tract excision. Technical refinements, including full-thickness flap design for complex cases and meticulous closure technique, optimise outcomes.^[21]

Comparative analysis reveals that flap success depends critically on tissue quality, with well-vascularised, non-inflamed tissue essential for healing. Anterior fistulas in women, traditionally challenging, respond favourably to advancement flaps given preservation of the limited anterior sphincter complex.^[22] However, the technique requires specific expertise and demonstrates learning curve effects, with outcomes improving significantly with surgeon experience. Failure rates increase substantially in the presence of active inflammation, suggesting timing optimisation remains crucial.

Laser ablation fistula laser closure (FiLaC)

FiLaC utilises radial-emitting laser fibres for controlled thermal ablation of fistula epithelium while preserving surrounding sphincter tissue.^[23,24] Standardised protocols employing 10–15 watts energy delivery report success rates of 60–75%, with particularly favourable results in straight, simple trans-sphincteric fistulas.^[25] The technique demonstrates excellent safety profiles with minimal postoperative morbidity and preserved anal function in 95% of cases.^[26]

Critical evaluation reveals important limitations: complex branching fistulas show significantly lower success rates (40–50%), suggesting FiLaC works best for straightforward anatomy. Recurrent fistulas demonstrate inferior outcomes compared to primary cases, likely reflecting tissue quality issues. Long-term data beyond 3 years remain limited, raising questions about durability. Cost considerations are significant, with equipment expenses potentially limiting widespread adoption. Despite these limitations, FiLaC represents a valuable option for appropriately selected patients, particularly those prioritising minimally invasive approaches with rapid recovery.

Video-assisted anal fistula treatment (VAAFT)

VAAFT technology enables direct fistuloscopic visualisation and selective electrocoagulation of fistula epithelium combined with internal opening closure.^[27,28] Contemporary protocols incorporating staged approaches for complex cases report success rates of 65–80%, with superior outcomes in primary versus recurrent fistulas.^[29] The technique offers theoretical advantages of precise visualisation and targeted treatment while minimising tissue destruction.

Analysis of accumulated evidence reveals mixed results across institutions, suggesting significant operator dependency. Success rates vary widely (45–85%) between centres, likely reflecting technical expertise differences and patient selection criteria.^[30] The technique demonstrates particular utility in complex cases where traditional surgery poses high risk, serving as an alternative when other sphincter-preserving approaches fail. However, equipment costs and learning curve considerations limit widespread implementation. Current evidence supports selective use in specialised centres with appropriate expertise rather than routine first-line application.

Bioengineered plugs and biomaterials

Contemporary bioengineered plugs utilising advanced collagen matrices and growth factor supplementation report success rates of 60–70%, representing improvement over first-generation devices.^[31,32] However, critical analysis of aggregate data reveals substantial heterogeneity in outcomes, with success rates ranging from 30 to 85% across studies.^[33] Patient selection emerges as a crucial determinant: short, straight tracts without significant inflammation demonstrate optimal results, while complex anatomy or active sepsis correlate with failure.

Comparative effectiveness analysis suggests that plug outcomes remain inferior to surgical techniques such as LIFT or advancement flaps for most indications.^[34] High material costs combined with modest success rates raise cost-effectiveness concerns. Current evidence supports consideration primarily for patients unable or unwilling to undergo more invasive surgery, or as an adjunct to other techniques rather than standalone therapy.

Adipose-derived mesenchymal stem cells (AD-MSCs)

AD-MSCs demonstrate potent anti-inflammatory, immunomodulatory and regenerative properties essential for fistula healing.^[35,36] The landmark ADMIRE-CD phase III trial established the efficacy of allogeneic AD-MSC therapy, demonstrating 50% combined remission rates versus 34% with placebo at 24 weeks in Crohn’s disease-associated fistulas.^[37] Subsequent analyses revealed particularly favourable outcomes in cryptoglandular fistulas, with success rates approaching 60–70% in selected cases.^[38]

Critical evaluation identifies several key considerations: Treatment effects appear most pronounced in complex fistulas refractory to conventional surgery, suggesting a role as salvage therapy. The optimal cell dosing, delivery method and retreatment protocols remain incompletely defined, with ongoing trials addressing these parameters.^[39] Cost represents a significant limitation, with single treatments exceeding several thousand dollars. Long-term durability data beyond 2 years remain sparse, though available evidence suggests sustained benefit in responders.^[40] Serious adverse events remain rare, with excellent safety profiles across multiple trials.

Integration into clinical practice

Current evidence supports selective integration of stem cell therapy for complex, treatment-refractory fistulas after conventional approaches have failed or when surgical options carry prohibitive functional risks.^[41] Patient selection criteria should emphasise complex anatomy (multiple tracts, high trans-sphincteric), previous surgical failures and acceptable tissue quality without active infection. The therapy appears particularly valuable for patients prioritising functional preservation over immediate cure rates, given modest success rates balanced against minimal morbidity. Ongoing research focuses on combination approaches integrating stem cells with surgical techniques, early results suggesting potential synergy.^[42]

Standardisation and protocol development

The field requires standardised treatment protocols based on robust evidence from large-scale, multicentre randomised controlled trials.^[55,56] Current literature limitations include heterogeneous patient populations, variable outcome measures and insufficient long-term follow-up beyond 2 years.^[57] Development of consensus guidelines incorporating contemporary evidence and expert opinion will facilitate optimal treatment selection and improve patient outcomes.^[58] International collaborative efforts are essential for generating the large datasets necessary for definitive recommendations, particularly for novel techniques where single-centre experience remains limited.

Personalised medicine integration

Future anal fistula management should increasingly utilise personalised medicine principles incorporating clinical, anatomical and potentially molecular data.^[59,60] Predictive algorithms integrating imaging characteristics, patient factors and biomarkers may optimise treatment selection while minimising unnecessary interventions. Integration of artificial intelligence-assisted decision support tools shows promise for standardising treatment approaches and improving outcomes, though it requires prospective validation.^[61] These approaches necessitate substantial investment in research infrastructure and clinical validation before routine implementation.^[62-106]