Comparison of the proposed new classification of anal fistulas with the Garg classification
1. Executive Summary
The classification of anorectal fistulas has transitioned from purely descriptive anatomical labeling toward management-centric frameworks designed to dictate surgical intervention and mitigate the morbidity profile of fecal incontinence. Historically, the Parks and St. James University Hospital (SJUH) systems provided the necessary foundation for anatomical categorization. However, the Garg classification, introduced in 2017, marked a definitive strategic shift by centering treatment decisions on the quantitative extent of External Anal Sphincter (EAS) involvement. This briefing evaluates the established Garg system alongside a newly proposed 2025 classification, which seeks to refine anatomical granularity through imaging-guided discovery.
The primary conclusion of this clinical analysis is that while the proposed 2025 system introduces valuable anatomical nuances—specifically regarding the subdivision of the intersphincteric space and novel landmarks like the "outerphincteric space"—its clinical performance and management implications remain fundamentally congruent with the Garg classification. Both systems successfully utilize the "one-third EAS involvement" threshold as the pathognomonic boundary between simple and complex disease. For the practicing surgeon, the choice between these systems involves weighing the utility of descriptive granularity against the streamlined efficacy of the Garg protocol; regardless, both provide the necessary precision for sphincteric preservation.
2. The Strategic Evolution of Fistula Classification
The evolution of fistula frameworks reflects a shift from "labels" to "roadmaps." Traditional descriptive models often failed to provide the clinician with a clear surgical mandate, leading to unacceptable variability in outcomes. Modern systems prioritize the protection of the external anal sphincter as the primary surgical objective.
The following table contrasts the traditional descriptive paradigm with the management-centric logic of the Garg classification.
The Strategic "So What?" The Garg system revolutionized perianal surgery by establishing the 1/3 EAS involvement threshold as the definitive contraindication for fistulotomy. This classification provides an immediate strategic directive: if the tract involves more than one-third of the EAS, the clinician must pivot to sphincter-saving interventions to avoid the catastrophic risk of postoperative incontinence.
3. Structural Comparison: The Garg System vs. The Proposed 2025 Model
The differentiator in the 2025 classification is its pursuit of greater anatomical granularity, incorporating recent imaging landmarks to provide a high-resolution map of the perianal region.
Introduction of Grade 0 (Submucosal Fistulas) and the CLM: The 2025 model introduces Grade 0 for submucosal fistulas. The Conjoint Longitudinal Muscle (CLM) serves as the critical anatomical boundary here. While Garg groups these as Grade I (intersphincteric), the new model distinguishes "inner intersphincteric" (between CLM and Internal Anal Sphincter) from "middle intersphincteric" (between CLM and EAS).
Strategic Significance of Grade II (High Intersphincteric): A critical differentiator is the categorization of Grade II lesions. These are unique, challenging fistulas that ascend within the intersphincteric plane above the dentate line without reaching the supralevator space. Both systems recognize these as a strategic middle ground between simple linear tracts and complex transsphincteric disease.
External Anal Sphincter (EAS) Metrics: Both systems remain tethered to the 1/3 EAS involvement rule. Grades I-II represent "Simple" disease (EAS ≤ 1/3), while Grades III-V represent "Complex" disease (EAS > 1/3).
Supralevator Categorization (Grade V vs. Subtype C): The Garg system treats supralevator involvement as a primary determinant of the highest severity grade (Grade V). Conversely, the 2025 model treats it as a concomitant feature (Subtype C) that can be applied across various grades.
Novel Anatomical Landmarks: The 2025 model integrates the "outerphincteric space"—the space between the EAS and the Garg fascia. Identifying these spaces is crucial for tracking complex pathways of spread.
4. Clinical Management Guidelines and Surgical Decision-Making
Classification systems are the foundation of the Garg Protocol, ensuring the surgical approach minimizes recurrence while maximizing sphincteric preservation.
Low/Simple Fistulas (Grades I-II)
Criteria: Low linear tracts involving ≤ 1/3 of the EAS.
Surgical Approach: Fistulotomy is the gold standard.
Expected Success: Success rates are excellent, exceeding 95% for Grade I and 90% for Grade II. Note that Grade II intersphincteric fistulas require greater care due to their extension above the dentate line.
High/Complex Fistulas (Grades III-V)
Criteria: Tracts involving > 1/3 of the EAS, or those with comorbidities.
Surgical Mandate: Fistulotomy is strictly contraindicated. Management requires advanced sphincter-saving procedures, including:
Ligation of Intersphincteric Fistula Tract (LIFT)
Video-Assisted Anal Fistula Treatment (VAAFT)
Anal Fistula Plug (AFP)
Transanal Opening of Intersphincteric Space (TROPIS)
Over-the-Scope-Clip (OTSC)
Fistula Laser Closure (FiLac)
Fistulectomy with Primary Sphincter Reconstruction (FPR)
Safety Warning (Grade IV-A): For fistulas associated with an acute abscess, FPR and AFP must be avoided. These cases, along with Grade IV (horseshoe/multiple tracts) and Grade V (supralevator), should be referred to a fistula specialist.
5. Critical Evaluation of Efficacy and Validation Metrics
The objective validation of surgical classifications remains challenging due to institutional and operator variability.
The "Surgical Failure" Critique: The 2025 system’s use of surgical failure rates as a primary validation tool is methodologically suspect. Failure rates are confounded by surgeon experience and institutional resources, making them a variable metric for evaluating the inherent accuracy of a classification system.
Predictive Accuracy and Correlation: The only currently accepted validation metric is the "positive correlation" between severity grade and failure risk. Both the Garg and 2025 systems demonstrate that as the grade moves from I to V, complexity and the risk of surgical failure rise linearly.
Fistulotomy Suitability: While the 2025 system claims higher precision in predicting suitability for fistulotomy, the expert consensus suggests that both systems perform with nearly identical accuracy in defining fistula complexity and guiding the preservation of the external sphincter.
6. Final Synthesis and Conclusion
The Garg and 2025 classifications provide robust frameworks for the modern colorectal surgeon. The Garg classification remains the global benchmark for management-guided intervention, having established the 1/3 EAS involvement rule to safeguard patient continence. The 2025 system offers descriptive depth, particularly regarding the CLM boundary and the Garg fascia, which may enhance high-resolution MRI interpretation.
Ultimately, the management implications of both systems are fundamentally congruent. The strategic value of any system lies in its ability to protect the external anal sphincter and guide the clinician toward the appropriate intervention. Whether adopting the streamlined Garg grades or the granular 2025 subtypes, the clinical objective remains constant: the accurate identification of complex tracts to prevent surgical failure and preserve long-term quality of life.
