ACCURACY OF TRANSPERINEAL ULTRASOUND RELATIVE TO MAGNETIC RESONANCE IMAGING IN EVALUATION OF PERIANAL FISTULAS

Abstract

Background
 Ano-rectal fistula is a chronic inflammation of perianal tissues affecting 1/10.000 individuals. Traditionally, treatment is surgical with the possibility of recurrence reaching up to a quarter of cases, therefore preoperative appropriate evaluations and imaging are necessary to decrease recurrence rate. 
 Objectives 
 Determining accuracy of transperineal ultrasound relative to magnetic resonance imaging in evaluation of perianal fistulas. 
 Methods
 A prospective study was conducted on 51 patients with clinically diagnosed perianal fistula. Transperineal ultrasound (TPUS) and magnetic resonance imaging (MRI) were done for all patients. The following variables were recorded by each of the tests and the results were compared one to one: Firstly the number of the tracts, their relation to the anal sphincters. Secndly the number of internal openings, their sites and distances from the anal verge. Thirdly any associated findings, including perianal abscess, extension (branching) or local inflammatory phlegmons. Descriptive statistics were used. P-values ≤ 0.05 were considered statistically significant.
 Results
 Relative to the MRI, the accuracy of TPUS in detection of fistula tract was 96%. Finding of at least one relation of the tract to the anal sphincter was 86.7%, detection of internal opening was 82%, and localization of the internal opening was 82% with comparable result in measuring their distance from the anal verge (P value = 0.15). Lastly the overall accuracy of TPUS to find at least one associated finding was 92%. Among detected associated findings, TPUS was able to accurately classify them with no significant difference between TPUS and MRI (P-Value > 0.05). Three superficial fistula tracts were detected by TPUS and proved by surgical operation while they were undetectable by MRI.
 Conclusion
 TPUS is an accurate imaging investigation in the evaluation of perianal fistula and its results was comparable to those of MRI in preoperative assessment of perianal fistula diseases.