Background: To correlate the operative findings of patients with fistula-in-ano with preoperative MRI and quantify the information added with MRI.
Methods: All consecutive fistula-in-ano patients operated between July 2013 and May 2015 were prospectively enrolled. Preoperative MRI was done in every patient. The details of tracts, internal opening and "complex parameters" (additional tract or additional internal opening, horseshoe tract, associated abscess and supralevator extension) found at surgery were compared to the findings determined by MRI.
Results: A total of 229 patients (424 tracts) with mean age-49.0 ± 11.3 years were included. M/F 198/31. James hospital classification: Type I 58, II 20, III 49, IV 86 and V 16. The sensitivity and specificity of MRI in diagnosing fistula tracts were 98.8 and 99.7%, respectively, and in identifying internal opening were 97.7 and 98.6%, respectively. MRI added significant information in 46.7% (107/229) patients which was presence of additional tracts in 71 (66.3%), horseshoe tract in 63 (58.8%), supralevator extension in 16 (14.9%), unsuspected abscess in 11 (10.3%) and multiple internal openings in one patient (1%). The proportion of simple/complex fistula (based on history and clinical examination alone) was 32.8/67.2% which changed to 21.4/78.6% after the MRI scan. MRI added significant information about unsuspecting complex parameters which were missed on history and clinical examination in more than one-third (26/75: 34.6%) of simple fistulae and more than half (81/154: 52.5%) of already known complex fistulae.
Conclusions: MRI is highly accurate in diagnosing fistula-in-ano and added significant information about unsuspected complex parameters in over one-third (34.6%) of simple and in half (52.5%) of complex fistula-in-ano.