Diagnostic Accuracy of MR Fistulography using Saline in the Evaluation of Perianal Fistula

Abstract

BACKGROUND Magnetic resonance imaging is known to demonstrate the perianal anatomy accurately. MR Fistulography with saline as contrast agent has been described to facilitate the detection of fistula tracks. We wanted to study the diagnostic accuracy, sensitivity, specificity, positive and negative predictive values of magnetic resonance fistulography using saline as a contrast agent using surgical findings as a reference standard. METHODS Fifty-nine clinically diagnosed cases of perianal fistulae who were sent for preoperative MR imaging of the perianal fistulae were included in the study. MR imaging after instillation of saline was obtained in these patients through a cannula inserted into the external opening. T2 and STIR images in axial and coronal planes were studied. Diagnostic indices were calculated using surgical findings as reference standard. RESULTS MR imaging with saline instillation demonstrated a sensitivity of 97.92 % in the detection of primary tracks. The sensitivity in determination of internal opening, secondary tracks, abscesses and horseshoe tracks were 98.04 %, 95.24 %, 100 % and 100 % respectively. MRI had 100 % specificity in detection of primary tracks, internal opening, secondary tracks, abscesses and horseshoe tracks before and after instillation of saline. The sensitivity was found to be more in participants who did not have active perianal discharge at the time of MR examination. CONCLUSIONS MRI with instillation of saline into the fistulous track is highly accurate for the presurgical evaluation of perianal fistula with respect to accurate depiction of primary track, secondary track, abscess and horseshoe extensions. It can serve as a cheaper alternative to MR examination using I.V. Gadolinium based contrast agents or MR Fistulography using Gadolinium agents. KEYWORDS Magnetic Resonance Imaging (MRI), Perianal Fistula, Saline, Pre-Operative Assessment, Fistulography, Horseshoe, Internal Opening, Secondary Tracks