Veena Madireddy1 , Shivani Gogi2 , Ashwini3 , Vijaya Kumari M.4
BACKGROUND Perianal fistula is an inflammatory pathological condition affecting soft tissues around the anal canal causing morbidity and requires surgical management and often has high tendency for recurrence. MRI has high accuracy in its preoperative assessment owing to high soft tissue contrast and guides in localization of the fistula, internal opening, ramifications and any associated abscess. Hence MRI plays an important role in planning treatment strategy, which is based on the type of perianal fistula and the degree of the involvement of adjacent tissues. We wanted to detect primary fistulous tract, determine the periodicity as acute or chronic. establish the relation of fistulous tract to sphincter complex, determine the position of the internal opening of the fistulous tract in relation to the anal clock, detect any cranial extension of the tract above levator ani muscle, identify any secondary fistulous tracts, any abscess to avoid surgical failure and recurrence and correlate accuracy of MRI with surgical staging. METHODS MRI Fistulography was done on 40 patients over a period of 12 months using 1.5 T AVANTO SIEMENS machine using T1, T2, STIR imaging in axial, coronal and sagittal views. MRI was found to have 97.29 % sensitivity, 66.66 % specificity, 94 % positive predictive value and 50 % negative predictive value and overall diagnostic accuracy is 95 %. RESULTS In the present study, during a period of 12 months, 40 patients were evaluated with MR fistulography. It was found to be highly sensitive in identifying the internal opening of fistula and secondary tracts, abscess formation, supralevator and horseshoe extension. Most common was grade II in 15 patients, followed by grade I in 9 patients, grade 3 in 6 patients and grade 4 in 6 patients and 4 patients had grade V and commonest internal opening was at 6 O’ clock position. MRI findings were concordant with surgical findings in 36 patients, one patient with grade 1 was found to be grade 3 on surgery and 2 patients as grade 1 on MRI were found to be simple perianal sinuses on surgery and other one was only a fibrosed tract. CONCLUSIONS MR Fistulography has emerged as an imaging technique of choice for preoperative evaluation of perianal fistula providing highly accurate rapid non-invasive means of performing pre-surgical assessment of fistula and is highly sensitive in the detection of primary tract, internal opening, secondary tract, abscess, and horseshoe extension along with its relation to pelvic structures and its complications on comparison with operative observations.
