Incidence of Perianal Fistula and Its Clinical Spectrum Following Perianal Abscess: A Prospective Observational Study

Abstract

Background: Perianal abscess is a common anorectal condition arising from cryptoglandular infection, and a substantial proportion of patient’s progress to fistula-in-ano despite adequate incision and drainage. Reported incidence rates of fistula formation vary widely (20-56%), and the factors that predict progression remain incompletely defined, particularly in Indian settings.

Aim: To estimate the incidence of perianal fistula in patients with perianal abscess, to assess its clinical spectrum, and to identify factors associated with fistula development.

Methods: This prospective observational study included 92 patients with perianal abscess managed by incision and drainage at a tertiary care hospital. Patients were followed up for the development of fistula-in-ano, and demographic, clinical, microbiological, and postoperative variables were analysed for their association with fistula formation using the chi-square test (p<0.05 significant).

Results: Fistula-in-ano developed in 40.2% (37/92) of patients. Recurrent abscess (53.2% vs 26.7%, p=0.02), abscess depth ≥3 cm (70.8% vs 6.8%, p<0.001), pus volume ≥15 ml (45.5% vs 13.3%, p=0.01), fecal organisms on culture (69.2% vs 18.9% with skin flora, p=0.0001), and delayed wound healing beyond 30 days (57.7% vs 27.8%, p=0.04) were significantly associated with fistula formation. Age, sex, occupation, education, residence, addiction, comorbidities, and antibiotic choice showed no significant association.

Conclusion: Fistula-in-ano is a common sequela of perianal abscess, occurring in two-fifths of patients, and its development is driven predominantly by disease severity and microbiological profile rather than demographic factors. Early identification of deep, recurrent, or fecal-flora-associated abscesses may help target patients for closer follow-up.