Diagnostic Accuracy of Magnetic Resonance Imaging in Detection of Perianal Fistula keeping Surgical Findings as Gold Standard

An abnormal connection between the rectum or canal and the anal skin is called as a perianal �stula (PAF). MRI is considered as a gold standard for the imaging of PAF because of its operator dependence, non-invasive nature, excellent soft tissue contrast, superior �eld of view and multiplanar capabilities . Objective: To assess the validity of magnetic resonance imaging in detecting perianal �stulas while using surgical �ndings as the gold standard. Methods: From 1 January 2021 to 30 January 2022, a cross-validation research was carried out in the radiology department at Memon Medical Institute Hospital in Karachi, Pakistan. The research comprised 153 individuals with PAF ranging in age from 18 to 70 years and of either gender. A 1.5 T MR scanner was used to obtain the MRI. All techniques used a phased-array coil for image capture in all circumstances. The imaging volume encompassed the distal rectum, anal canal, and subcutaneous tissues. Fat saturation pictures were taken in the oblique, axial, and coronal planes. A radiologist examined images, and pertinent patient data were noted on a pre-drafted proforma. Histopathological and post-surgical results were acquired and documented. Results: The validity of MRI for the diagnosis of PAF was 82.4% by taking surgical �ndings as gold standard. Conclusion: For the assessment of PAF and the detection of abscesses, MRI is a bene�cial and reliable preoperative examination.

stulectomy, and patients with cardiac pacemakers indwelling metallic implants were not included in the study.Written informed permission was obtained from patients presenting with discharging perianal sinus on physical examination and referred to the department of radiology for MRI of pelvis for PAF after approval from the institutional review board.A 1.5 T MR scanner was used to obtain the MRI.All techniques used a phased-array coil for image capture in all circumstances.The imaging volume encompassed the distal rectum, anal canal, and subcutaneous tissues.Fat saturation pictures were taken in the axial, oblique, and coronal planes.A radiologist reviewed the images and noted important patient data on the pre-drafted proforma.Histopathological and postsurgical results were acquired and documented.SPSS version 22.0 was used to enter and evaluate the acquired data.For numerical data, mean and standard deviation were presented.For categorical data, frequency and percentage were presented.Using surgical results as the gold standard, the 2 by 2 table was utilized to compute validity of MRI for the detection of PAF.

M E T H O D S
endosonography, computed tomography, 3D ultrasounds, MRI and trans perineal ultrasound, have all been utilized in the past to identify PAF [7].Cannulating the exterior aperture and injecting a water-soluble contrast into the stula are both components of traditional stulograms.The relationship between the tract, the external or internal sphincter, and the levator ani muscle is invisible clear because the major tract and its extensions do not ll with contrast when blocked with debris or pus, and the sphincter muscle feature is not observable [8].Transrectal ultrasound enhances the ability to see stulae and the connection they have to the muscles of anal sphincter.However, it has limitations including operator dependence, no imaging coronal plane and a small eld of view [9].CT stulography is restricted by the fact that the brosis areas, stula tract, and sphincter muscles all have comparable attenuation values.Multidetector row CT stulography, with its isotropic voxels, is anticipated to enhance the outcomes of modality [9,10].However, MRI is considered as a reference standard for the imaging of PAF because of its operator dependence, non-invasive nature, excellent soft tissue contrast, superior eld of view and multiplanar capabilities [1,2].In addition, MRI can properly diagnose the stula tract in relation to the sphincter complex and its related problems such as abscesses and secondary tract [3].A recent study found that MRI is 100% sensitive and 88% speci c for the identi cation of PAF, and concluded that MRI has great sensitivity but low speci city for the diagnosis of PAF [11].The role of MRI is well established in Western nations, however local data is sparse in this area [5][6][7]11,12].Therefore, the goal of current study is to assess the validity of MRI for the detection of PAF by considering surgical ndings as gold standard.This investigation would aid in establishing the accuracy of MRI in preoperative evaluation of PAF in ano, allowing needless radiation and diagnostic delay due to incomplete tract healing by granulation tissue to be avoided, as is the case with traditional stulography.It would also assist to reduce unneeded procedures and complications.
It was a cross-validation study conducted at the department of radiology of Memon Medical Institute Hospital (MMIH), Karachi from 1st Jan 2021 to 30th Jan 2022.Sample size of 153 patients was estimated using WHO sample size calculator by taking proportion of in ano as 20% [13], bond on error as 6.4% and 95% con dence level.The research included all probable patients with PAF (had a perianal external skin opening or having watery, blood-tinged, or purulent discharge from the opening) aged 18 to 70 years of either gender.Patients who had surgery for perianal stula, those with recurrent perianal sinus opening with histor y of perianal

R E S U L T S
The overall mean age was 45.11±15.22 years with range 20 to 69 years.There were 69 males (45.1%) and 84 females (54.9%) patients in the study.The overall duration since diagnosis on conventional MRI/ Surgery was 3.46±1.18weeks ranging from 1 to 5 weeks.MRI ndings showed PAF in 107 (68%) patients and no in ammation in 46 patients (32%) (Figure 1).

D I S C U S S I O N stula (n=153)
Traditional stulography, computed tomography, and ultrasound have all failed to diagnose disease accurately [10,14].The MRI role in the assessment of stula-ano was originally established by Koelbel et al., in 1989, and followed by several researchers [2,15].We also tested the diagnostic accuracy of MRI for detecting perianal stulas in the current investigation, considering surgical ndings as the gold standard.In our study, the Sn of MRI for PAF diagnosis using surgical ndings as gold standard was 87.7%, the Sp was 70.2%, and the diagnostic accuracy was 82.4%.In their study, Singh et al.,

C o n  i c t s o f I n t e r e s t
The authors declare no con ict of interest.

S o u r c e o f F u n d i n g
The author(s) received no nancial support for the research, authorship and/or publication of this article.

Figure 1 :Figure 2 :
Figure 1: Frequency distribution of MRI ndings for perianal stula (n=153) Singh et al., reported a PPV value of 98% for MRI in  their study [2].Because of the small sample size in this research, more studies with a larger sample size and based in multi-hospitals are needed.In this way, the ndings may be generalizable to wider populations.
For the assessment of PAF and the detection of abscesses, MRI is a bene cial and reliable preoperative examination.

Table 1 :
Validity of MRI ndings for the identi cation of PAF by taking surgical ndings as gold standard