Magnetic resonance imaging with dynamic contrastenhancement in perianal fistula staging

Aim: To investigate whether dynamic contrast enhanced perfusion T1-weighted (DCE T1-W) three-dimensional volume interpolatedbreath-hold examination (3-D vibe) contributes to perianal fistula staging. Materials and Methods: A total of 110 patients who underwent pelvic magnetic resonance imaging (MRI) (1,5 tesla, Siemens, Avanto)with the preliminary diagnosis of perianal fistula were included in our retrospective study. In our perianal fistula MRI protocol, DCET1-W 3D vibe sequence was in axial plane with fat-saturation and in five phases (precontrast phase and then in the $45^{th}$, $60^{th}$, $180^{th}$ and $240^{th}$ seconds after intravenous contrast administration). Perianal fistula staging was performed according to T2-weightedsequence findings (acute, subacute, chronic) and by clinical history. Semi-quantitative measurements of the perianal fistula weremade with the ROIs placed on the perianal fistula and left femoral artery. Then measurements were made as follows: Type ofcontrast curve obtained, staining peak time and slope angle of the curve. All measurements were performed independently by tworadiologists at different times. Interobserver agreement was also evaluated (Cohen’s kappa). Results: The phases of reaching the peak time (TTP) of contrast increases as the perianal fistula stage increases (mean phases ofTTP values were$2.2^{th}$± 1.2 in acute phase fistulas, $2.8^{th}$ ± 1.2 in subacute perianal fistulas; $4.4^{th}$ ± 1 in chronic fistulas). The angleof inclination decreased as the stage of the perianal fistula increased (42.2 ± 13.2 degrees; 27 ± 11.3 degrees and 9.6 ± 2.3 degrees,respectively). Conclusion: Diagnosis of perianal fistula with physical examination can be confusing. Sometimes there can be fistulas with differentstages in the same patient. Therefore, the use of IV contrast-enhanced pelvic examination with dynamic technique may provideinformation about the perianal fistula stage.

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