BACKGROUND: Intralunimal ultrasonography is a new imaging technique in the diagnostic work-up of proctologic diseases. Anal fistulas can also be visualised especially if hydrogen peroxide (H2O2) is injected as a constrast agent. The aim of the study was to determine the usefulness of endoanal ultrasound in the preoperative evaluation of anal fistulas, particularly in patients with complicated fistulas such as Crohn's disease or with recurrent manifestation.
METHODS: During a study period of six years a total of 191 anal fistulas in 182 patients (9 patients with 2 seperate fistulas) were examined using endoanal ultrasound. 115 patients were male and 67 female, with a median age of 44 (14-78)years. 30 patients (16.5%) suffered from Crohn's disease and 19 (10.5%) had recurrent anal sepsis. The vast majority of fistulas (93%) were visualised using H2O2 and studied with a 360° real-time-image ultrasound probe. 132 patients (75.5%) underwent operative treatment. The accuracy of the endosonographic diagnosis was assessed by comparing the preoperative classification (according to Parks) with the intraoperative finding.
RESULTS: Fistulas were classified endosonographically as follows: transsphincteric n=78, intersphincteric n=46, suprasphincteric n=15, subanodermal n=30, recto-vaginal n=17, and other fistulas n=5. 122 (92.4%) of the 132 fistulas which were treated operatively had been classified correctly preoperatively. The accuracy for patients with Crohn's disease and recurrent fistulas was 81% and 82%, respectively.
CONCLUSION: Endoluminal ultrasonography is a valuable technique in the preoperative assessment of fistula-in-ano. It delineates the precise anatomy of the fistula track with regard to the anal sphincter and aids surgical planning in the more complex cases, e.g. in patients with recurrent and/or Crohn's disease. However, endosonographic interpretation of fistulas is an operator-dependent examination and requires substantial experience in this field.