Abstract
ObjectiveTo evaluate intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) sequences for quantitative characterization of anal fistula activity.MethodsThis retrospective study was approved by the institutional review board. One hundred and two patients underwent MRI for clinical suspicion of anal fistula. Forty-three patients with demonstrable anal fistulas met the inclusion criteria. Quantitative analysis included measurement of DCE and IVIM parameters. The reference standard was clinical activity based on medical records. Statistical analyses included Bayesian analysis with Markov Chain Monte Carlo, multivariable logistic regression, and receiver operating characteristic analyses.ResultsBrevity of enhancement, defined as the time difference between the wash-in and wash-out, was longer in active than inactive fistulas (p = 0.02). Regression coefficients of multivariable logistic regression analysis revealed that brevity of enhancement increased and normalized perfusion area under curve decreased with presence of active fistulas (p = 0.03 and p = 0.04, respectively). By cross-validation, a logistic regression model that included quantitative perfusion parameters (DCE and IVIM) performed significantly better than IVIM only (p < 0.001). Area under the curves for distinguishing patients with active from those with inactive fistulas were 0.669 (95% confidence interval [CI]: 0.500, 0.838) for a model with IVIM only, 0.860 (95% CI: 0.742, 0.977) for a model with IVIM and brevity of enhancement, and 0.921 (95% CI: 0.846, 0.997) for a model with IVIM and all DCE parameters.ConclusionThe inclusion of brevity of enhancement measured by DCE-MRI improved assessment of anal fistula activity over IVIM-DWI only.
Highlights
Anal fistulas are common, with an incidence of 8.6 per 100,000 population [1]
Regression coefficients of multivariable logistic regression analysis revealed that brevity of enhancement increased and normalized perfusion area under curve decreased with presence of active fistulas (p = 0.03 and p = 0.04, respectively)
Analysis of dynamic contrast-enhanced (DCE)-magnetic resonance imaging (MRI) signal-intensity curves revealed that brevity of enhancement provided separation between inactive and active anal fistulas
Summary
With an incidence of 8.6 per 100,000 population [1]. Underlying causes include Crohn’s disease, pelvic infection, trauma, malignancy, and radiation therapy [2]. MRI has become a technique of choice for imaging anal fistulas because of its ability to identify tracts, define complex anatomy, and detect abscesses [4, 7,8,9,10]. Assessment of fistula activity plays a critical role in the selection of medical, surgical, or combined therapy [11,12,13] and patient outcome [4, 14, 15]. The detection of abscesses and fistula extensions by MRI can guide the surgeon to resect occult pathological structures that may be otherwise refractory to immunosuppressive therapy, potentially resulting in better patient outcomes [16]
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