Purpose: This study was conducted to determine agreement between hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and endoanal magnetic resonance imaging in the preoperative assessment of perianal fistulas and to compare these results with the surgical findings.
Methods: Twenty-one patients (aged 26-71 years) with clinical symptoms of a cryptoglandular perianal fistula and a visible external opening underwent preoperative hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography, endoanal magnetic resonance imaging, and surgical exploration. The results were assessed separately by experienced observers blinded as to each other's findings. Each fistula was described with notice of the following characteristics: classification of the primary fistula tract according to Parks (intersphincteric, transsphincteric, extrasphincteric, or suprasphincteric), horseshoe, or not classified; presence of secondary tracts (circular or linear); and location of an internal opening.
Results: The median time between hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and endoanal magnetic resonance imaging was 66 (interquartile range, 21-160) days; the median time between the last study (hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography or endoanal magnetic resonance imaging) and surgery was 154 (interquartile range, 95-189) days. Agreement for the classification of the primary fistula tract was 81 percent for hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and surgery, 90 percent for endoanal magnetic resonance imaging and surgery, and 90 percent for hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and endoanal magnetic resonance imaging. For secondary tracts, agreement was 67 percent for hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and surgery, 57 percent for endoanal magnetic resonance imaging and surgery, and 71 percent for hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and endoanal magnetic resonance imaging in case of circular tracts and 76 percent, 81 percent, and 71 percent, respectively, in case of linear tracts. Agreement for the location of an internal opening was 86 percent for hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and surgery, 86 percent for endoanal magnetic resonance imaging and surgery, and 90 percent for hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and endoanal magnetic resonance imaging.
Conclusions: For evaluation of perianal fistulas, hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and endoanal magnetic resonance imaging have good agreement, especially for classification of the primary fistula tract and the location of an internal opening. These results also show good agreement compared with surgical findings. Therefore, hydrogen peroxide-enhanced three-dimensional endoanal ultrasonography and endoanal magnetic resonance imaging can both be used as reliable methods for preoperative evaluation of perianal fistulas.