Cryptoglandular Anal Fistula: Epidemiology, Etiology, and Classification Systems

Cryptoglandular anal fistulas arise from infection of the anal glands and can develop into a chronic, recurrent condition in which treatment must balance fistula healing with preservation of continence. Although relatively uncommon in the general population, they frequently affect adults in their working years, with persistent drainage, pain, and repeated interventions imposing a substantial burden on quality of life. Understanding this burden begins with the relationship between anorectal abscess and fistula formation, traditionally explained by glandular obstruction and infection that progresses through the intersphincteric plane. While this cryptoglandular model remains central to understanding disease development, emerging evidence suggests that inflammatory signaling, immune dysregulation, and tissue remodeling also contribute to persistence. These mechanisms distinguish cryptoglandular disease from other causes of anal fistula, particularly Crohn’s disease, and provide context for understanding the anatomical patterns that guide classification and treatment. As knowledge of these patterns has advanced, classification systems have evolved from clinical observations, such as Goodsall’s rule, to the anatomical framework established by Parks and subsequent approaches incorprating imaging and functional risk. Within this evolution, magnetic resonance imaging has improved recognition of secondary tracts, associated abscesses, and extensions that may otherwise remain undetected, informing both the St. James’s University Hospital classification and contemporary multidimensional systems such as the Garg classification. By combining these anatomical findings with sphincter involvement, baseline continence, and prior treatment, clinicians can better assess fistula complexity and select an appropriate operative approach. This chapter reviews these developments alongside the epidemiology and pathogenesis of cryptoglandular anal fistulas, emphasizing how an integrated understanding of disease biology and classification supports surgical planning, patient counseling, and the pursuit of durable healing while preserving function