Incidence and factors influencing the development of fistula-in-ano after incision and drainage of perianal abscesses

Objective: The aims of the present study were to evaluate the incidence of fistula-in-ano following incision and drainage of acute perianal abscess and to determine factors influencing the fistula formation. Material and Method: Patients with a first-time perianal abscess or intersphincteric abscess who underwent incision and drainage at Siriraj Hospital from January 2005 to June 2008 were reviewed. Patients with coexisting fistula or perianal Crohn's disease were excluded. Incidence and risk factors for fistula formation were analyzed. Results: Sixty-four patients were reviewed (50 males, 14 females). The average age of the patients was 44 years (range 19-82). The average follow-up period was 30 months (range 10-53). Twenty patients (31%) developed fistula-in-ano following incision and drainage. Gender, smoking, alcohol consumption, fever, leukocytosis, and location of abscess were not predictive of fistula formation. Univariate analysis showed that patients aged under 40 years and non-diabetic patients tended to have a higher risk for developing the fistula (43% vs. 21%, OR 2.95, 95% CI 0.98-8.85; p = 0.05 and 38% vs. 13%, OR 4.2, 95% CI 0.85-20.83; p = 0.071, respectively). However, patients receiving perioperative antibiotics (ATB) were less likely to develop subsequent fistula in both univariate and multivariate analysis. The FIA rate in non-ATB group was 48% and only 17% in ATB group (OR 4.5, 95% CI 1.44-14.13; p = 0.01). Conclusion: The incidence of fistula-in-ano following incision and drainage of perianal abscess was 31%. Patients aged under 40 years and non-diabetic patients appeared to have a higher risk for fistula formation. Administration of perioperative antibiotics significantly reduced the rate of subsequent fistula formation.