Abstracts
1997 Digestive Disease Week

Accuracy of endoanal ultrasonography in evaluating anal fistulas.

AJN Iroatulam, JJ Nogueras, HH Chen, EG Weiss, FM Potenti, O Alabaz, SD Wexner. Department of Colorectal Surgery, Cleveland Clinic Florida, Fort Lauderdale, FL.

AIM: The aim of this study was to evaluate the accuracy of endoanal ultrasonography in defining the anatomy of anal fistula tracts. METHODS: A retrospective review of all patients with anal fistula who underwent endoanal ultrasonography (EAUS) was performed. Correlation of EAUS results and intraoperative findings on the bases of operative report was accomplished. All patients underwent office-based endoanal ultrasonography with Bruel and Kjaer Real Time Ultrasound Scanner type 1846 using a 7.0 MHz probe. Hydrogen peroxide was used for fistula tract image enhancement. Fistula anatomy was classified using Park's classification system. Collateral findings as well as patient's tolerance of the procedure were also evaluated. RESULTS: Between 1992 and 1996, 65 patients, 50 males and 15 females of mean age of 49 (range 21-86) years underwent EAUS with diagnosis of anal fistula. EAUS findings were positive in 53(81.5%) patients, 39 males and 14 females of mean age of 47.3(range 21 -86) years. Hydrogen peroxide was used for image enhancement in 35(66%) patients. Findings included 43(93.7%) transsphinteric fistulas, 2(4%) intersphinteric and 1(1.9%) extrasphinteric fistula. 21(39.6%) patients had a history of prior fistula surgery, and 12(22.6%) patients had a diagnosis of Crohn's disease. Perineal abscess was detected in 2(3.7%) patients and no fistulous tracts could be traced in 5(9.4%) patients. 38 (83%) of these 46 patients underwent surgery based on ultrasonography and findings at surgery were compared with ultrasonographic results.

US        SURGERY       ACCURACY
 Transsphincteric fistula         35          31            88.6%
 Intersphincteric fistula          2           1             50%
 Extrasphincteric fistula          1           1            100%

The overall accuracy in defining fistula tract anatomy was 91.6%. The 5 patients in whom no fistulous tracts were identified have not required surgery to date. CONCLUSION: Endoanal ultrasonography is an accurate, minimally invasive, well tolerated test useful in defining the fistula tract anatomy.