Endoanal ultrasound in perianal fistulas and abscesses.

Anal ultrasound has demonstrated to be accurate in staging perianal cryptoglandular fistulae and fistulae in Crohn's disease. When there is an external fistula opening, H2O2 can be introduced with a plastic infusion catheter. The tract becomes then visible as a hyperechoic lesion ('white'). It has been shown that this corresponds excellent with surgical findings. It is equally sensitive as endoanal MRI. Because recurrent cryptoglandular fistulae are complex in about 50% and Crohn's fistula in 75%, it is mandatory to perform anal ultrasound preoperative in these patients to avoid missed tracks during surgery and subsequent recurrences. Anal ultrasound can also be used to monitor (medical) therapy in patients with Crohn's disease. Especially considering the easiness of performing and lesser costs then MRI, endoanal ultrasound merits more attention.