Purpose: To prove the diagnostic value of color Doppler US in the evaluation of perianal external fistulae, using an endocavitary probe and a saline solution injection, in order to show the location of the fistulae, their extension, possible secondary tracts, residual abscesses and the relationship with adjacent tissues.
Material and methods: From October 1999 to December 1999, thirty-five consecutive patients (21 males and 14 females, mean age 47.5) affected with Crohn's disease were examined prospectively. These patients presented postoperative recurring external perianal fistulae. From this first group, 10 patients (6 males and 4 females, mean age 45) were selected as the external fistula was open. A biplanar transrectal 7.5 MHz probe was used for the examination. First the external opening of the fistula was cannulated with a soft plastic catheter. Then the probe, covered with a lubricated condom filled with US gel, was introduced into the anal canal (males) or the vagina (females). An initial gray-scale US study was performed. Finally the color-box was positioned on the tract, the Pulse Repetition Frequency (PRF) adjusted and the saline solution introduced. The study was completed with axial and linear scans.
Results: The mean examination duration was 31 minutes. Only two patients found the examination annoying because of partial anorectal stricture. The wall layers and their thickness were clearly located and distinguished. Gray-scale US showed the local anatomy in all patients. In 4 patients it depicted the primary fistula as a thin hypoecoic line (40%, three intersphinteric and one transphinteric). Color Doppler US detected the fistula in all patients (100%, seven intersphinteric and three transphinteric). Moreover it showed 2 small secondary tracts in 2 patients. No abscesses were found at the time of the examination. In the patients who underwent a second operation, surgical findings showed a good correlation (90-100%) with color Doppler findings.
Discussion and conclusions: This study demonstrated a greater diagnostic value of endosonography with color Doppler and saline solution injection as compared to conventional gray-scale endosonography in the evaluation of fistulae. Since this technique is also cost-effective and well tolerated by most patients we conclude that at present it makes an important diagnostic tool in the preoperative assessment of perianal fistulae.