Comparison of endoanal magnetic resonance imaging with surgical findings in perirectal sepsis

Background A small percentage of patients presenting with perirectal sepsis will have complicated or recurrent disease. In these cases, clinical examination may be difficult or unreliable and accurate preoperative imaging may be of value. Methods A prospective study using a specially designed internal coil for magnetic resonance imaging (MRI) was carried out in ten patients with simple cryptogenic perirectal sepsis and in 11 patients with complex recurrent disease. Fistulas and abscesses were classified independently by a colorectal surgeon unaware of the results of MRI and a radiologist unaware of the operative findings. Results In patients with simple perirectal infection, endoanal MRI accurately detected all abscesses and four of five fistulas. In complicated cases (multiple recurrences, sepsis secondary to inflammatory bowel disease or where the fistula track(s) traversed the main sphincter complex), endoanal MRI identified six of seven abscesses with confirmation of abscess site and horseshoe configuration when present in all cases. Surgical and radiological concordance was present in 12 of 14 fistulas with identification by MRI of the internal opening in nine of 12 cases. Conclusion Endoanal MRI provides high-resolution images of the relationship of collections and tracks to the levator plate and is recommended in the evaluation of complex or recurrent perirectal sepsis.