This systematic review and meta-analysis evaluated the diagnostic accuracy of MRI-based apparent diffusion coefficient (ADC) and diffusion-weighted imaging (DWI) for differentiating active from inactive perianal fistulas.

The protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO) (CRD42024596604). The review included five databases (MEDLINE, Cochrane Library, PubMed, Science Direct, and Google Scholar). Meta-analyses were performed on studies reporting ADC values and other sequences using STATA software with the "Midas" command.

Of 21 studies included in the review, 12 were meta-analyzed, encompassing 1007 patients (77.5 % male) with 1092 fistulas and 321 abscesses. Six studies reported ADC values for active vs. inactive fistulas, with a pooled sensitivity of 83 % (95%CI 68-92), specificity of 75 % (95%CI 60-85), and AUC of 0.85 (95%CI 0.81-0.87). Pooled ADC cut-offs ranged from 1.105 to 1.109 × 10⁻³ mm2/s. The T2WI + DWI sequence demonstrated the highest diagnostic accuracy, with a pooled sensitivity of 99 % (95%CI 90-100), specificity of 97 % (95%CI 79-100), and an AUC of 1.

ADC alone is inadequate for reliably distinguishing active from inactive fistulas. T2WI combined with DWI offers superior diagnostic performance, surpassing contrast-enhanced T1WI, and is promising for non-invasive evaluation of perianal fistulas. However, several limitations, such as moderate to high risk of bias and heterogeneity, may bias this conclusion.

T2WI + DWI could become the standard for assessing perianal fistulas, avoiding contrast agents, and benefiting patients contraindicated for Gadolinium-based contrast media. Variability and potential bias across studies warrant further research.

Perianal fistula is clinically diagnosed and commonly characterized using magnetic resonance imaging (MRI). Diffusion-weighted imaging (DWI) and T2-weighted imaging are emerging techniques that can obviate the need for contrast injection in cases where contrast administration is not feasible or contraindicated. The main objective of our study was to compare the efficacy of the combination of DWI and T2 STIR (short tau inversion recovery) imaging with contrast-enhanced MRI for the diagnosis and characterization of perianal fistula.

Sixty-nine patients with clinical perianal fistula with at least one external opening were evaluated with DWI, T2 STIR, and contrast MRI. A comparative cross-sectional study was conducted in the Department of Radiodiagnosis and Imaging, All India Institute of Medical Sciences, Bhopal, India. The chi-square test was done to find the association between categorical variables. The Kappa test was done to estimate the agreement between two different tests in measuring the outcome. The validity of tests was measured using sensitivity, specificity, positive predictive value, negative predictive value, and accuracy.

The combination of DWI and T2 STIR is equivalent to contrast-enhanced MRI in the evaluation of primary and complicated perianal fistula. The combination of DWI and T2 STIR is superior to DWI alone in the classification and characterization of perianal fistula. However, DWI is superior to T2 STIR in differentiating perianal inflammation with abscess from perianal inflammation without abscess and can be used as an alternative to post-contrast fat-suppressed T1-WI in the detection of perianal abscesses and disease activity.

DWI can be used as an adjunct to T2 STIR, and the combination of DWI and T2 STIR can replace the post-contrast fat-suppressed T1 MRI sequence in the classification and characterization of perianal fistula.

The purpose of this study was to explore whether preoperative diffusion-weighted magnetic resonance imaging (DW-MRI) can be used to evaluate the prognosis of anal fistula and identify the influence factors of postoperative recurrence.

This is a retrospective study of 117 patients with anal fistula who have undergone preoperative DW-MRI and surgery. All patients were followed up by telephone or reexamination within 2 years after surgery. Of the 117 patients, 35 were excluded due to loss of follow-up and only 82 were included in this study. MRI fistula imaging-related data were analyzed, and fistula severity was scored using criteria of both local extension of fistulas and active inflammation for a total maximum score of 22. The apparent diffusion coefficient (ADC) value of the fistula in patients with anal fistula during preoperative MRI examination was measured. According to whether anal fistula patients are accompanied by perianal abscess, they are divided into two groups, namely anal fistula group and anal fistula with abscess group. Based on whether patients with anal fistula recur after surgery, they were further divided into recurrent group and non-recurrent group.

82 patients with anal fistula were included in this analysis, 23 of them recurred and 59 were cured. Among patients with perianal abscess, the mean ADC value of the recurrent group was (1.19 ± 0.21)×10^-3 mm²/s, which is significantly lower than that of the non-recurrent group (1.36 ± 0.19)×10^-3 mm²/s. There were significant statistical differences in ADC values between the two groups (p = 0.03). Among patients with anal fistulas without abscesses, 15 patients recurred after surgery, with a mean ADC value of (1.45 ± 0.27) ×10^-3 mm²/s, and 33 patients didn't occur, with a mean ADC value of (1.44 ± 0.31)×10^-3 mm²/s. The ADC value of preoperative fistula in patients was negative significant correlation with MRI findings score (r= -0.332, P = 0.002). Risk factors for the recurrence after anal fistula surgery include the time interval between MRI and operation, multiple fistula tracks. Fatigue, excessive intake of spicy or greasy food and diarrhea may also be external risk factors for postoperative recurrence of patients with anal fistula.

DW-MRI has important application value for the prognosis evaluation of anal fistula. Complex type of anal fistula and improper lifestyle are the main risk factors affecting the recurrence after anal fistula surgery.