The Value Of MR Multiple Sequences In Showing The Morphology Of Anal Fistula And DTI In Evaluating Its Activity

Anal fistula refers to the anomalous connection between the anal canal or rectum and the skin around the anus,which the granulation tissue is lining the anal fistula and is the typical result of the healing of perianal abscess.The retention of bacteria in the fistula can cause a chronic infection,and the accumulation of secretions and necrotic tissue can obstruct the fistula,with the manifest of continuous or intermittent discharge of pus from the external orifice.Anal fistula is a common disease in anorectal surgery.It occurs on any age and the average age is between 20-40,which is more in male and the ratio of male to female is about 5:1.The incidence of anal fistula is high,but the clinical cure rate is relatively low,with the reason of ignoring the hidden secondary fistula or small abscess which results to a relatively high recurrence rate.There are many methods for preoperative evaluation of anal fistula,the initial fistulography is a more economical,convenient method but not accurate.CT scan is limited because of its poor soft tissue resolution.Although ultrasonography is a non-invasive examination,it is still slightly inferior to MRI in the evaluation of anal fistula due to poor imaging of tissues farther away from the probe.MRI is currently recognized as the best method for detecting,describing and evaluating the details of anal fistula.It provides the most detailed information about the relationship between the anal and sphincter complexes and between the fistula and pelvic floor structures.It can accurately locate the main fistula and identify secondary fistula and abscess.The routine sequences of MRI are contained of T1WI,T2WI,FS T2WI and FS T1WI contrast-enhanced.It is emphasized in the literature the important usefulness of the T2WI,FS T2WI and FS T1WI contrast-enhanced sequences.There is few reports about the application of DWI sequences and the comparative study of different sequence combinations,especially the comparative study between MRI contrast-enhanced sequences and other sequences on morphology performance of the anal fistula.In addition,the use of MR contrast agents is relatively contraindicated in patients with renal insufficiency,and the risk of renal systemic fibrosis is significantly increased.So many studies are looking for a noninvasive method to assess anal fistula.Another important value of MRI lies in evaluating the activity of the anal fistula,which is of great significance in guiding the choice of treatment timing and surgical methods.In order to choose the best treatment method and operation time to reduce the recurrence effectively,it is very important to correctly evaluate the activity of anal fistula inflammation and obtain more accurate imaging information about the disease before operation.It has been reported in the literature that DWI sequence is useful in quantitatively evaluating the activity of anal fistula.However,there is not literature about the value of diffusion tensor imaging in evaluating the activity of anal fistula as a quantitative and non-invasive method.Purpose1.To compare the lesion conspicuity and diagnostic performance rate of four imaging data sets(FS T2WI,DWI,combined FS T2WI and DWI[FS T2WI+DWI],FS T1WI contrast-enhanced[FS T1WI+CE])in assessing perianal fistulas,and to explore the best sequence to evaluate the morphology changes of anal fistula.2.To explore the value of magnetic resonance diffusion tensor imaging(MR DTI)in evaluating the activity of anal fistula as a quantitative and noninvasive method.Materials and methodsPart ?:A comparative study of MR multiple sequences in evaluating the morphological changes of anal fistula:Forty-six patients(39 males and 7 females)with anal fistula,aged 18-80 years(mean 41.67±2.18,with a median of 39.5 years)were enrolled.The main clinical manifestations were perianal swelling,fever or pain.There was a fistula or a hard knot around the anus.And sometimes purulent or bloody discharge could be seen.The longest history was 10 years,while the shortest was 5 days.All the patients underwent 3.0T MRI routine sequence,DWI sequence and FS T1WI contrast enhancement scanning within 1 week before surgical treatment,and were confirmed as anal fistula by surgery and pathology.With the consent of the hospital ethics committee,all patients were informed of the condition before examination,and the informed consent was signed by the patient or legal guardian.All patients were scanned with 3.0T Siemens MR scanner(Siemens,Skyra 3.0T),covered with 18-channel body coil,in supine position with head first,with the symphysis pubis as the center.No intestinal preparation was required.The routine MRI protocol comprised of axis T1-weighted imaging(Turbo Spin Echo(TSE),coronal T2-weighted imaging,axis and sagittal T2-weighted imaging with fat suppression,followed by diffusion weighted imaging(DWI).Finally,the volume acquisition technology(VIBE)was used to conduct T1-weighted with fat suppression sequence before and after intravenous gadolinium administration(gadodiamide,0.1mmol/kg,with the injection rate of 2.5ml/s,and 20ml saline injected at last).After the scanning,the images were transmitted to the PACS.The surgical pathology results were taken as the standard.Two physicians with more than 8 years' experience in MR diagnosis analyzed and evaluated the images independently.After the initial independent analyses,the results were discussed by the two observers and modified if necessary,applying a consensus reading method.All images were obtained in axial plane.Recording the detection of internal opening,main fistula,secondary or branch fistula or abscess of anal fistula on the transverse images of FS T2WI,DWI,FS T2WI +DWI,FS T1WI+CE.According to the Parks classification,the anal fistula could be divided into 4 types.According to 4-point scale in the references by Hori and the definition,contour and margin of the internal opening and fistula,and the relationship between them with the sphincters,scored each sequence on the conspicuity and diagnostic performance rate of the internal openings and fistulas on a 4-point scale:1,probably not a fistula or an internal opening;2,uncertain or indistinct;3,possible a fistula or an internal opening but obscure;and 4,definite and legible fistula or an internal opening.Statistical analysis were done with the software package SPSS 25.0.Kappa conformance test was performed on the two observers:k?0.4,poor consistency;0.4<k?0.6,medium consistency;0.6<k?0.8,good consistency;k>0.8,very good consistency.The diagnostic performance rate of the anal fistula were compared with chi-square test;the conspicuity scores of the internal openings and fistulas were compared with rank test.A P-value of less than 0.05 was considered to indicate a statistically significant difference.Bonferroni correction(n=4)was used for multiple comparisons,a P-value of less than 0.008((2 X 0.05)/4(4-1))was considered to indicate a statistically significant difference.Part II:Magnetic resonance diffusion tensor imaging in evaluating anal fistula activity:Preliminary study:34 patients with perianal fistula were analyzed with examination on conventional magnetic resonance imaging and diffusion tensor imaging.All patients underwent MRI examination within 1 weeks before operation,and proved to be anal fistula by surgery and pathology.All the patients met the standard of Clinical guidelines for the diagnosis and treatment of anal fistula,having no contraindication of MRI scan.With the consent of the hospital ethics committee,all patients were informed of their condition and informed consent was obtained before the examination.34 patients were examined in a 3.0 T Philips MR scanner(Intera,Philips Medical Systems,Best,the Netherlands),covered by the body coil,in supine position with head first,with symphysis pubis as the center.Patients were asked to empty the stomach 4-6 hours and empty the bladder half an hour before the examination.Routine MRI sequences included T1WI,T2WI,and T2WI-SPAIR.The scan positions were axial,sagittal and coronal.In addition to identifying the primary fistula,secondary fistula or abscess,and judging the morphological character,course and the type of anal fistula,the more important thing was to observe the relationship between fistula and the anatomical structure around and the involvement of the sphincter complex.The b value(diffusion sensitivity coefficient)of DTI was 0,400 s/mm2,with 32 diffusion directions.The parameters of DTI were TR 3250 ms,TE 48 ms,thickness 5 mm,without interval,slices 20,FOV 152mm X 179mm,5 minutes 47 seconds.After the acquisition,the data were transmitted to the Extended MR Workspace.Two physicians with more than 8 years' experience in MR diagnosis analyzed and evaluated the images independently.After the initial independent analyses,the results were discussed by the two observers and modified if necessary,applying a consensus reading method.According to the preoperative examination and surgery requirements,the lesions were divided into two groups:the active inflammation(PIA)group and the inactive inflammation(NIA)group.After obtaining the FA and ADC maps,the largest layer of the primary fistula was selected for measurement.The ROI was first drawn on the DTI(b=0)images on the center layer of the fistula with the reference of T2WI and T2WI-SPAIR.The area of ROI was not less than 10mm2.And then the ROI was copied to the FA and ADC maps of the same plane.The FA and ADC values of the lesion were obtained subsequently.Each lesion was measured and the result were recorded to get the average.With the findings in and post operation and pathology,all statistical analyses were conducted with the Statistical Package 15.8.Independent sample t test was used to compare the DTI paramers in the two groups.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,specificity,Jordan index and the area under curve.In all tests,P<0.05 represented statistically significant differences.ResultsI.In 46 cases of anal fistula,a total of 51 internal openings,62 primary fistulas and 34 abscesses were found in surgery,with two internal orifices found in 5 patients,and 3 horseshoe fistulas.The consistencies of the two observers about the four sets were good.The set of FS T1WI+CE,FS T2WI+DWI,FS T2WI were superior to DWI set on the conspicuity and diagnostic rate of the internal orifice.The set of FS T1WI+CE,FS T2WI+DWI were superior to FS T2WI set and DWI set on the conspicuity of the anal fistula.2.According to St James's University Hospital MR Imaging Classification of perianal fistulas,the numbers of fistulas in each grade of the PIA group were:Grade 1-0,Grade 2-9,Grade 3-1,Grade 4-6 and Grade 5-6,and the numbers of fistulas in each grade of the NIA group were:Grade 1-7,Grade 2-3,Grade 3-2,Grade 4-0 and Grade 5-0.The anal fistula of the PIA group were generally distributed in Grade 2,4 and 5,and the anal fistula of the NIA group were generally distributed in Grade 1,2 and 3,mainly in Grade 1.The FA and ADC values of PIA group were 0.134 ±0.046,0.979 ±0.441(X 10-3mm2/s),and the FA and ADC values of NIA group were 0.183 ±0.057,1.393±0.256(×10-23mm2/s)respectively.The values of FA and ADC in PIA group were lower than those in NIA,and the difference was statistically significant.The AUC value of the FA value was 0.753(95%CI 0.575-0.884)and the difference was statistically significant(P=0.0052).The cut-off value of FA was 0.15,the sensitivity was 69.23%,the specificity was 76.19%,the Youden index was 0.4542.The AUC value of the ADC value was 0.751(95%CI 0.573-0.883).The cut-off value of ADC was 1.069(XI 10-3mm2/s),the sensitivity was 100.00%,the specificity was 57.14%,and the Youden index was 0.5714.Conclusion1.The conspicuity and diagnostic performance rate of FS T2WI combined with DWI were comparable to that of FS T1WI contrast enhancement.The combination of FS T2WI and DWI could be the best sequence for noninvasive evaluation of anal fistula morphology changes.2.DTI parameters can reflect the quantitative information of tissues,FA and ADC values could be used as a reference for surgeons to evaluate the activity of anal fistula,and as a guide for the choice of surgical timing and treatment methods.DTI is a non-invasive and quantitative method for preoperative evaluation of anal fistula.3.MRI could assess the morphology and activity of anal fistula accurately,which is of great guiding significance for the treatment of anal fistula.