Complex perirectal sepsis: clinical classification and imaging

Background The use of specialized imaging to assess cryptogenic fistula-in-ano is selective, aimed at delineation of the site of the internal fistula opening and the relationship of the primary and secondary tracks and collections to the main levator plate. Advanced imaging also permits definition of the destructive effects of perirectal sepsis (e.g. internal or external anal sphincter damage, perineal body destruction and an ano- or rectovaginal fistula), which may require secondary reconstructive surgery. Methods We performed a PubMed search of outcomes for fistula management in the English and non-English literature, and summarized results regarding the accuracy of internal opening and horseshoe detection as well as the operative correlation for cryptogenic and non-cryptogenic fistula-in-ano using endoanal ultrasound (EAUS) and magnetic resonance (MR) imaging. Only literature defining these characteristics was included. Results The advantages and limitations of the main forms of imaging are discussed in this review with emphasis on EAUS and endoanal or pelvic phased-array MR fistulography. The new technique of transperineal sonography is highlighted. A small but important group of patients with complex fistula-in-ano require specialized imaging. There are specific limitations of endoanal ultrasound (EAUS) which necessitate pelvic phased-array MR imaging. Initial work suggests that EAUS may have a role in intraoperative use for image-guided drainage of recurrent abscesses where operative interpretation can be difficult. The coloproctologist in a tertiary referral center must acquire the skills of ultrasound performance in order to successfully treat fistulous disease, suggesting a role for formal imaging accreditation as part of coloproctological training. Conclusion Future studies should determine both what sequential imaging algorithms for imaging are cost-effective as well as predictive of fistula cure.