Fistulas in ano: endoanal ultrasonographic assessment assists decision making for surgery.

Eighteen patients with a clinical impression of a complex fistula in ano, had anal endosonography to delineate the anatomy of the fistula track and identify associated areas of sepsis. The clinical impression of a complex fistula was refuted by endosonography and subsequent surgical exploration in two cases. Horseshoe tracks were identified in nine (50%) patients and fluid collections, not evident on clinical examination were identified in eight (45%) patients. Accurate identification of the internal opening with a 7 MHz transducer was possible in two (11%) cases. External sphincter damage was evident in four (22%) patients. Surgical findings matched endosonographic appearances in all but one case (94%). Anal endosonography is an accurate and minimally invasive method of delineating the relation of fistula tracks to the anal sphincters and identifying deep areas of sepsis in relation to such fistulas.