This study was a prospective analysis study, approved by the ethics committee at our institute and was conducted during the period from December 2018 to December 2020.
Fistular activity was confirmed by intra-operative findings (considered as the standard reference) by differentiating the cases into two groups (positive and negative inflammatory groups) based on the presence of necrotic tissues, pus and other inflammatory products.
Patient characteristics
Sixty-two patients were included in this study (Fig. 1), fifty-five (88.7%) were males and seven (11.3%) were females with age ranging from twenty-three to sixty-nine with mean ± SD of 38.74 ± 10.51. Their age ranged from 23 to 69 years (mean age 38.74 ± 10.51).
The forementioned patients were referred to the radiology department by surgery outpatient clinic requesting preoperative MRI assessment. Based on the surgery conclusions and clinical evaluation (performed by two surgeons of 4 years -resident- and 8–10 years’ experience -senior registrar/consultant-).
Different types of fistulae were diagnosed, thirty-three of the cases were of inter-sphincteric type (fifteen active and 18 inactive) seventeen were of the trans-sphincteric type (twelve active and 5 inactive) and twelve cases were of the extra-sphincteric type (five active and 7 inactive).
All the referred patients were operated upon by senior surgeon (consultant) with 8–10 years’ experience—who were blinded as regards the MRI DWI/DTI findings—and stated in their feedback that patients with inter-sphincteric fistulae were operated upon by simple fistulotomy (Lay open) technique while trans-sphincteric and extra-sphincteric cases were operated upon by sphincter preserving techniques mainly fistulectomy (coring) and repair of the sphincter if needed.
These patients were divided accordingly into two groups: the positive inflammation activity (PIA) group -being thirty-two (51.6%)-with thirty males and two females- and the negative inflammation activity (NIA) group -being thirty (48.4%)- with twenty-five males and five females.
Inclusion criteria
Patients proved to have perianal fistulae that require preoperative assessment.
Exclusion criteria
These involved patients that underwent previous surgical intervention, patients who lack conclusive operative data of fistular activity, patients with absolute MRI contraindications as having pacemakers or intracranial aneurysmal clips as well as claustrophobic patients.
MR imaging
MRI was performed using 1.5 Tesla magnet scanner by two devices (Intera and Achieva, Philips medical system). All patients were examined in the supine position using a surface coil, Subjects were required to empty their bladders before the examinations. No sedation was used.
The MRI imaging protocol included the following sequences:
Turbo spin echo (TSE) T1-weighted imaging (T1WI): axial; TR/TE, 600/10 ms; field of view (FOV), 200 × 200 mm2; matrix, 400 × 400; slice thickness, 5 mm; and number of slices, 20. TSE T2-weighted imaging (T2WI): axial, sagittal and coronal; TR/TE, 1560/80 ms; FOV, 200 × 200 mm2; matrix, 400 × 400; slice thickness, 5 mm; and number of slices, 20. Short T1 inversion recovery imaging (STIRWI): axial, sagittal and coronal; 200–300 ms; matrix, 236 × 147 mm2; slice thickness, 5 mm; and number of slices, 20. DWI and DTI (spin echo-echo-planar imaging, SE-EPI): axial; TR/TE, 3250/48 ms; FOV, 200 × 200 mm2; matrix, 80 × 80 with a 112 × 112 reconstructed matrix; slice thickness, 5 mm; number of slices, 20; 32 diffusion-weighed directions; NSA, 1; b = 0.400 s/mm2. Other b values acquisition was done in some cases with b = 400, 600 and 1000 s/mm2. Respiratory triggering was used for better resolution.
Post processing and image analysis were conducted as follows and qualitative as well as quantitative analysis of the MR images were conducted as a double-blinded analysis by two radiologists one with 5 years (R.E.) experience and the other with 15 years (H.A.) experience.
Qualitative analysis
Restricted diffusion was determined by visualization of abnormal bright signal intensity that became enhanced with increasing b values at “Diffusion weighted” (DW) images. The ADC map presented intermediate/low signal intensity (SI) that corresponded to the abnormality. The DTI images were fused with T2/STIR WI to allow the assessment of the anatomical details.
Quantitative analysis
The ADC values were measured manually by applying ROI on the DTI (b = 0) fused images on the largest suspected area, and overlaid on FA and ADC maps, and the average value was obtained by measuring 3 times. In addition, the lesions were divided into 4 ROIs (i.e., the fistula area, edema area, ipsilateral affected sphincter area and distant normal-appearing contralateral sphincter area).
Statistical analysis
All statistical analyses were conducted with the Statistical Package for Medical Statistics (Medcalc15.8, Ostend, Belgium; https://www.medcalc.org). All the FA, ADC values are presented with mean ± standard deviation (x ± s). The FA and ADC values of each area were calculated and analyzed with single-factor analysis of variance (ANOVA). The DTI values of each group were statistically calculated with independent samples t tests. The cut-off values for the ADC and FA measurements in evaluating the activity of the lesions were obtained by receiver operating characteristic (ROC) curve analysis, as were the sensitivity and specificity. In all tests, P < 0.05 represented statistically significant differences.
Sample size.
Epi-calc 2000 was used to calculate the sample size of this cross-sectional study. Assuming 80% power, 0.05 level of significance, 20% null hypothesis value and estimated proportion of 38%.
Sample size = 43.