European Journal of Cardiovascular Medicine

Fistula-in-ano is among the most prevalent anorectal disorders in adults, with a significantly higher incidence in males compared to females. A perianal fistula is defined as an abnormal tract connecting the epithelial lining of the anal canal to the perineal skin. The reported incidence ranges between 1 to 2 cases per 10,000 individuals, with a male-to-female ratio of approximately 2:1.

The cryptoglandular theory provides the most widely accepted explanation for its pathogenesis. According to this theory, obstruction of the anal glands—located within the crypts of Morgagni at the dentate line—leads to bacterial infection, resulting in abscess formation and eventual spontaneous rupture through the perianal skin. These glands may extend variably into the internal and external anal sphincters, influencing the complexity of fistula formation [1,2].

While cryptoglandular infections remain the primary cause, other etiologies of perianal sepsis include Crohn’s disease, tuberculosis, malignancies, trauma, and radiation therapy [3]. Clinically, patients often present with perianal discharge, pain, discomfort, and occasionally fever. However, some may remain completely asymptomatic [4,5].

Surgical excision of the fistulous tract remains the cornerstone of treatment, yet recurrence rates remain high—ranging from 25% to 30% [6]. This high failure rate is often due to incomplete identification of secondary tracts and hidden abscesses, which can result in persistent infection and necessitate further surgical intervention.

Traditional diagnostic tools such as digital rectal examination (DRE) and examination under anesthesia (EUA), although routinely used, frequently fail to delineate complex fistulous pathways accurately. This can lead to misclassification of the fistula and incomplete surgical management [7,8]. Similarly, imaging techniques like fistulography, endoanal ultrasound, and CT scans offer limited value, often performing no better than clinical evaluation in detecting secondary extensions and their relationship with the anal sphincter complex [7,9].

Magnetic Resonance Imaging (MRI) has emerged as the gold standard imaging modality for preoperative assessment of perianal fistulas. MRI provides a detailed view of the perianal anatomy, accurately characterizes the fistulous tract, and classifies it in relation to the pelvic diaphragm and anal sphincters. It is particularly effective in detecting hidden tracts and abscesses that may otherwise be missed intraoperatively, thus improving surgical outcomes and significantly reducing recurrence rates [4,5].

To standardize assessment, the St. James’s University Hospital classification system was developed. This MRI-based grading system classifies fistula-in-ano according to radiological anatomy seen on pelvic MRI, enabling a more precise and reproducible preoperative evaluation [9].

AIMS AND OBJECTIVES

• To study the role of the Magnetic resonance imaging in the pre operative mapping of fistulous tract as per St. James Hospital classification

To compare the findings of magnetic resonance imaging and operative findings and their influence on outcome of surgery.

This descriptive & prospective study was conducted patients of Fistula-in-Ano attending Surgery department, at GGS Medical College, Faridkot from January 2017 to October 2018, after obtaining ethical approval.  A nonrandom convenient sampling technique was used to include 50 consecutive patients with clinically diagnosed Fistula-in-Ano, in the study. Patients with recurrence of Fistula-in-Ano, metallic implants and claustrophobia were excluded.  Detailed clinical history and physical examination, including detailed per rectal examination for site, number, distance from anal verge, internal opening location was recorded. MRI Imaging was performed by Seimens Magnetron Avento 1.5 Tesla. First sagittal FSE T2W sequence were done showing correct orientation of anal canal; then coronal oblique images parallel to walls of the anal canal and axial oblique images perpendicular to the coronal planes were taken. The Fistula-in-Ano were classified with the St. James University Hospital Classification [Table 1][9] 

Table 1- St. James University Hospital Classification of Fistula-in-Ano

 All patients underwent operative intervention, on table, tract of fistula was mapped by injecting methylene blue. Intraoperative findings on nature of fistula, primary/secondary ramifications, relationship with spinsters and presence or absence of abscess were recorded. A comparison of MRI and operative findings was carried out and data was statistically analyzed using SPSS software.

A total of 50 patients were included in the study. Peak incidence of fistula in ano was recorded in the age group 31-40 years(38%-17patients) followed by age group 41-50. Male patients outnumbered the female patients. The male to female ratio was 4.5:1. 

In this study, perianal discharge (82%) was the most common presenting symptom followed by pain (62%) .47 patients had single opening while 3 patients had multiple openings. Out of 50 patients, 13 (26%) patients had the external opening anteriorly, and 37 patients (74%) had posteriorly. Findings as per St. James Hospital classification, are presented in Table 2.

TABLE -2 Distribution of patients based on MRI findings according to St James University Hospital Classification

MRI finding revealed primary fistulous tracts and internal openings in all our patients and secondary tracts in 32% of the patients with abscess in 10% and horseshoe tracts in 8% and supralevator extension in 4% patients. On operation table, tract of fistula was mapped by injecting methylene blue and carrying out meticulous dissection to delineate and record findings primary. Tract, secondary ramifications, presence of abscess (fistula anatomy). Fistulotomy was performed in 36% patients while 34 % of patients underwent fistulectomy. Setons were used in 16%, Ligation of intersphincteric fistula tract (LIFT) procedure was performed in 12% and diversion colostomy with complete excision of the tract by cutting the muscles and then primary repair of sphincteric muscle was performed in 4% patient.

TABLE -3 Distribution of patients based on surgery performed

Similar findings of characteristics of fistula in ano found on MRI (as per St James classification), collated with findings at surgery in 96 percent i.e. 48 patients (Table 4). In two patients there was a discordance between MRI and Per-operative findings. In First patient (reported as grade 1 St James on MRI), internal opening described by MRI was found to be a blind tract on surgery (& hence a sinus) and in another (reported as grade 4 St James on MRI),  MRI was not able to correctly delineate secondary tract which was found to be partially healed tract on surgery .

Table – 4 Comparison of MRI findings with findings at surgery

Figure 1- T1 weighed Post Contrast Images of Coronal Section Images showing Grade-I

Intersphincteric Perianal Fistula with Perianal Sinus (St James ‘University Hospital Classification)

Figure 2- T1 weighed Post Contrast Images of Axial Section Images showing Grade-II Intersphincteric Perianal Fistula (St James ‘University Hospital Classification)

Figure 3-T1 weighed Coronal Section with Contrast showing a Grade –IV Trans Sphincteric Perianal Fistula (St James ‘University Hospital Classification)

Fistula-in-ano is a challenging clinical condition associated with significant morbidity, primarily due to its high recurrence rates and the risk of fecal incontinence following treatment [11]. Although multiple surgical treatment modalities exist, successful management is often complicated by the intricate anatomy of the anal sphincter complex and the difficulty in identifying all fistulous extensions. The anal sphincter comprises two concentric muscular layers separated by the intersphincteric space, which contains fat. A thorough understanding of the relationship between the fistula tract and the perianal soft tissues is essential for accurate diagnosis and effective surgical planning [12].

Historically, imaging modalities were considered to have a limited role in the diagnosis and assessment of fistula-in-ano. However, various imaging techniques—such as traditional fistulography, computed tomography (CT), endoanal ultrasonography, and magnetic resonance imaging (MRI)—have been utilized with varying degrees of success [13].

X-ray fistulography, though previously used, is now largely obsolete due to its poor diagnostic accuracy. Studies report a sensitivity as low as 16% and a false-positive rate of 10% in identifying the internal opening and fistula extensions. Moreover, it is invasive, painful, requires probing, and carries risks including infection, sepsis, pain exacerbation, and creation of false tracts due to aggressive contrast injection [14]. CT imaging, although useful for detecting abscesses, lacks the soft tissue resolution required to clearly define the anatomy of the anal sphincter and fistula tracts, rendering it less effective for detailed evaluation [13].

In contrast, MRI has emerged as the gold standard investigation for fistula-in-ano, offering excellent soft tissue contrast and the ability to acquire high-resolution images in multiple planes. MRI allows for detailed delineation of the fistula tract, internal opening, secondary branches, and any associated abscesses or areas of occult sepsis [15]. This comprehensive anatomical mapping significantly enhances preoperative planning and reduces recurrence rates by ensuring more precise surgical intervention [16].

In the present study, which included 50 patients clinically diagnosed with fistula-in-ano, the majority were males (n=41, 82%), with a male-to-female ratio of 4.5:1. This gender disparity is consistent with prior studies and has been hypothesized to relate to the role of androgens and stronger anal sphincter tone in males [17–20]. The peak incidence was observed in the 31–40 years age group, accounting for 38% of cases, in line with previously published literature [17,21].

Clinically, the most common presenting symptom was perianal discharge (82%), followed by pain (62%). These findings closely resemble those reported by Rajput VV et al., who noted discharge in 93.82% of patients [22]. The posterior location of the external opening was the most frequently observed (74%), aligning with the findings of Emile et al., who reported posterior external openings in 71.4% of cases [23].

In our study, MRI findings correlated with intraoperative findings in 96% of cases (48 out of 50 patients), highlighting its high diagnostic accuracy. Similar findings have been reported by Daabis et al. and Kulvinder Singh et al., who found MRI sensitivity, specificity, and positive predictive value to be 95.56%, 80%, and 97.73%, respectively, for detecting and grading the primary fistulous tract [24,25].

Due to its high soft tissue resolution, MRI provides superior visualization of the internal opening, primary and secondary tracts, and associated abscesses compared to clinical examination. However, MRI is not without limitations. Healed fibrotic tracts may be misinterpreted as active fistulae, and vascular or neural structures can be mistaken for secondary tracts, resulting in false positives [26]. Nevertheless, MRI remains a powerful tool, with Perini et al. and Lunnis PJ et al. reporting 83–89% correlation with surgical findings [4,27], and Beckingham et al. documenting 97% sensitivity and 100% specificity when comparing MRI with surgical exploration [28].

Importantly, studies have shown that the timing of MRI interpretation in relation to surgery impacts outcomes. When surgeons were unaware of MRI findings at the time of surgery, correlation rates dropped. Schaefer O et al. reported a correlation of only 89% (32/36 cases) in such scenarios [29]. In contrast, Buchanan et al. demonstrated that when MRI findings were shared immediately before surgery, the operative plan was altered in 10% of cases, illustrating the utility of MRI in real-time surgical decision-making [31].

Blind surgical exploration of complex fistulae can lead to excessive dissection, resulting in postoperative incontinence and an increased likelihood of missing secondary tracts or abscesses, which predisposes to recurrence [32]. Despite the proven benefits, MRI use in low-resource settings remains limited due to cost, availability, and the need for specialized radiological expertise. The question of whether MRI should be universally employed in all cases of fistula-in-ano remains debated. While many authors advocate for routine MRI use in all patients [4,14,15,25], practical challenges in developing countries must be acknowledged.

This study has several limitations. It was conducted at a single center with a limited sample size. Additionally, surgeons were not blinded to the MRI findings, which precluded assessment of how preoperative MRI altered intraoperative decision-making or outcomes.

Preoperative magnetic resonance imaging amicably improves the surgeon’s knowledge of the perianal fistulas’ anatomy and provides a roadmap to increase precision in complicated fistula surgery. Hence, we recommend routine use of preoperative MRI in patients of fistula in ano, as convenience of preventing dreaded complication like incontinence & recurrence significantly outweighs the cost factor.

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