Background: Anal fistula anatomy and its relationship with anal sphincters are important factors influencing the results of
surgical management. Pre-operative definitions of fistulous track(s) and the internal opening play a primary role in minimizing damage to the sphincters and recurrence of the fistula.
Objective: To evaluate the relative accuracy of digital examination and endoanal ultrasound for pre-operative assessment of anal fistula by comparing operative findings.
Material and Method: A retrospective review was conducted of all patients with anal fistula admitted to the surgical unit between May 2008 and May 2012. Physical examination and hydrogen peroxide-enhanced endoanal ultrasound (utilising a 10 MHz endoprobe, HITACHI: EUB-7500), were performed in 142 consecutive patients. Results were matched with surgical
features to establish their accuracy in preoperative anal fistula assessment.
Results: A total of 142 patients (107 men, 35 women), 28 of whom had had previous surgery, were included in the study. Their mean age was 40 (range 18-71) years and their mean BMI was 26.37 (range 17.30-36.11) kg/m2. The majority of the fistulas were transphincteric (90.4%) and the rest were intersphincteric (9.6%). The accuracy rates of clinical examination and endoanal ultrasound were 55.63 and 95.07 percent (p<0.01), respectively.
Conclusion: Endoanal ultrasound is superior to digital examination for pre-operative classification of anal fistula.

Keywords: Fistula in ano, Endoanal ultrasonography, Clinical examination, Accuracy