Fistula in ANO is a long-standing condition with an abnormal perianal tract or cavity covered by granulation tissue that links the perianal skin with the anal canal. It occurs at an incidence of 1.2 to 2.8 per 10,000 people in various European nations and is more common in males, especially in their fourth decade of life, with a male-to-female ratio of about 2:1. A considerable percentage of patients who have an anorectal abscess, between 30% and 70%, are found to have a concomitant anal fistula, and one-third of them are detected within a month to one year following drainage of the abscess. Parks classified fistula in ano according to the tract's relationship with the anal sphincter muscles as intersphincteric, transsphincteric, suprasphincteric, and extrasphincteric types. Moreover, St. James University classification is commonly employed by radiographers, and other classifications, including Garg's classification, have been suggested. Steele et al. also classified anal fistulas as simple or complex, with simple fistulas being less than 30% of the external sphincter, whereas complex fistulas have more muscle involvement or are linked with conditions like inflammatory bowel

disease, pre-existing fecal incontinence, or radiation [1,2].

Imaging modalities are of great importance in outlining the anatomy of perianal fistulas, thus helping surgeons to recognize tracts and branches that contribute to fistula formation. X-ray fistulography, although utilized in the past, has poor sensitivity as it cannot accurately outline the entire tract. Magnetic resonance (MR) fistulography is regarded as the imaging modality of choice because it is highly sensitive in identifying fistulous tracts. Nevertheless, MR imaging is still restricted by high cost, long procedure time, and long waiting periods, which reduce its feasibility in resource-poor environments. Other patients also develop discomfort as a result of claustrophobia and prolonged immobility throughout the procedure. Conversely, CT fistulography has been investigated as a second-line imaging technique in some institutions, showing promise in defining the fistulous tract with greater availability and cost-effectiveness than MRI [3,4].

Surgical management of complex anal fistulas is problematic because of a high rate of recurrence and possible complications like fecal incontinence. Although seton placement has been used extensively as a sphincter-preserving method, research suggests that it might not be sphincter-preserving in nature, with postoperative incontinence rates ranging up to 63%. Other sphincter-sparing methods, such as endorectal advancement flap (ERAF), ligation of the intersphincteric fistula tract (LIFT), fibrin glue injection, anal fistula plug, fistula laser closure, and video-assisted anal fistula treatment (VAAFT), have been developed over the last few decades. The LIFT procedure, as modified by Rojanasakul et al., has also been found to have a high success rate of 94.4% without failure of continence. Moreover, the LIFT-plug technique, with the use of a bioprosthetic anal fistula plug, has enhanced healing rates from 83.9% to 94% and decreased the total healing time. Fistula-in-ano primary sphincteroplasty (FIPS), as advocated by Parkash et al., has been presented as a method of restoring the integrity of the sphincter, preserving keyhole deformity to a lesser extent and lowering the recurrence rate in comparison to standard fistulotomy. Other methods, like endoanal advancement flap repair, have demonstrated healing in the range of 66% to 87% in cryptoglandular fistula. Photodynamic therapy (PDT) has also emerged as a promising sphincter-sparing technique, utilizing light energy and photosensitizers to induce tissue healing, with reported success rates ranging from 65.3% to 80% [5-7].

Despite advancements in surgical techniques, delineating the fistulous tract remains challenging for both radiologists and surgeons. Even after curative surgical intervention, recurrence rates range from 10% to 40%, depending on the procedure performed. Although MR fistulography is regarded as the gold standard for fistula imaging, its limitations, including incomplete information about the fistulous course, pose challenges in intraoperative decision-making. Given the high cost and limited availability of MRI, alternative imaging modalities such as CT fistulography may offer a viable solution for preoperative evaluation. CT fistulography can potentially yield useful information about the amount of active inflammatory tissue, the number and position of internal and external openings, hidden tracts, and related abscesses. Moreover, its availability and ease of interpretation make it an attractive choice, especially in resource-poor healthcare environments [8].

Increased interest is developing in finding cost-effective diagnostic modalities for the assessment of perianal fistulas, especially in areas with limited access to MRI. Additionally, few studies in India have correlated imaging results with intraoperative findings. The present study seeks to determine the validity of CT fistulography in delineating the anatomy of fistulous tracts in patients who undergo surgery for fistula in ano. Multi-detector CT fistulography has shown promise in yielding detailed imaging of perianal fistulas and deserves further evaluation as an alternative imaging modality to MRI.

Study Design

This study was conducted as a cross-sectional analysis to evaluate the accuracy of CT fistulography in assessing fistula in ano in patients undergoing surgical intervention. The study aimed to compare preoperative CT fistulogram findings with intraoperative observations to determine the diagnostic precision of this imaging modality.

Study Participants

The study included all adult patients diagnosed with fistula in ano who attended the General Surgery Department at AIIMS Patna. Each participant provided informed consent before enrollment in the study. A thorough clinical examination was performed for all patients, and relevant findings were documented in a structured proforma. Patients presenting with clinical and investigative evidence of ano-rectal malignancy, active anorectal sepsis, contrast allergy, or a history of Crohn’s disease or tuberculosis were excluded. Additionally, patients who refused to give consent for surgical intervention were not included in the study.

Sampling and Sample Size Calculation

All eligible patients presenting with fistula in ano at AIIMS Patna during the study period formed the sampling population. The sample size was determined using the Taro Yamane formula for a finite population of 70, with a 5% margin of error, which resulted in a required sample size of 60. The sampling technique employed was convenient sampling to ensure a feasible yet representative selection of participants.

Preoperative Evaluation

Patients presenting to the General Surgery outpatient department with perianal discharge were systematically assessed. Demographic details such as name, age, sex, and socioeconomic status were recorded. A detailed clinical history, including comorbidities and past medical conditions, was obtained, followed by a comprehensive clinical examination that included digital rectal examination and proctoscopy. Laboratory investigations and radiological assessments, including CT and MRI fistulograms, were performed to evaluate the characteristics of the fistulous tract. The classification of fistulas was determined based on clinical examination, CT fistulogram findings, and MRI fistulogram observations.

Preprocedural Preparation for CT Fistulogram

Before undergoing CT fistulography, each patient underwent preparation to optimize the visualization of the fistulous tract. The tract was irrigated with a hydrogen peroxide and normal saline solution in a 1:10 dilution to enhance delineation. To prevent rectal mucosal irritation, gauze swabs were placed for protection. Care was taken to avoid the presence of air pockets within the tract, ensuring optimal contrast distribution for better imaging.

CT Fistulogram and Intraoperative Correlation

After pre procedural preparation, a CT fistulogram was done to evaluate the course of the fistulous tract. Parameters like tract length, ramifications, internal opening, type of fistula, and presence of abscess cavities were noted. Patients were then planned for surgery, and intraoperative findings were documented in a proforma. The surgical observations, including tract length, internal openings, and associated abscesses, were compared with the preoperative CT fistulogram findings to determine the diagnostic accuracy of the imaging modality.

Data Collection and Statistical Analysis

The study was conducted prospectively, and the patient details were recorded on a predesigned proforma. Each case was documented with a unique case record number, and all demographic, clinical, and investigative findings were systematically entered. Since follow-up visits were not required for this study, all necessary data were collected at the time of diagnosis and intraoperative assessment.

Statistical analysis was done using SPSS version 22 for Microsoft Windows. Continuous variables were described using measures such as range, mean, standard deviation, and median, while categorical variables were represented as frequencies and percentages. The Chi-square test was employed to compare categorical data, with Fisher's exact test used when expected frequencies were below five. A p-value of less than 0.05 was considered statistically significant. Standardization techniques were applied to variables such as age, sex, height, weight, and BMI to ensure accuracy in measurements and analysis.

Classification of Socioeconomic Status and BMI

Socioeconomic classification was determined using the Kuppuswamy’s Socioeconomic Status Scale (2019), which considers factors such as the education and occupation of the head of the family and total family income. BMI was categorized according to standard WHO criteria, classifying individuals as underweight, normal weight, overweight, or obese based on their body mass index values

Demographic and Clinical Characteristics

A total of 60 patients with anal fistulae were included in the study, with a mean age of 37.52 ± 13.07 years. The majority (36.7%, n=22) were aged 31–40 years, followed by 21–30 years (30.0%, n=18). Males constituted 78.3% (n=47) of the cohort (Table 1). Body mass index (BMI) analysis revealed 70% (n=42) of participants were within the normal range, while 30% (n=18) were overweight. No patients were underweight or obese (Table 2). A history of addiction was absent in 78.3% (n=47), with tobacco chewing (11.7%, n=7) and smoking (8.3%, n=5) being the most common habits. Comorbidities included diabetes (13.3%, n=8) and hypertension (10.0%, n=6) (Table 2).

Table 1: Age Distribution of Patients (N=60)

Table 2: Demographic and Comorbidity Profile (N=60)

Clinical Presentation and Fistula Characteristics

All patients presented with perianal discharge (100%, n=60), while 38.3% (n=23) reported pain. Posteriorly located external openings were most common (48.3%, n=29), followed by anterior (28.3%, n=17) and lateral (11.7%, n=7) positions. In 6.7% (n=4), no external opening was identified. Per Parks classification, transsphincteric fistula predominated (71.7%, n=43) over intersphincteric (28.3%, n=17) (Table 3). CT fistulograms revealed a mean tract length of 4.38 ± 1.64 cm, with 96.7% (n=58) having a single tract. Intraoperative findings confirmed these results.

Table 3: Parks Classification of Fistulae (CT vs. Intraoperative)

Agreement between CT and Intraoperative Findings

CT demonstrated perfect agreement with surgery for classifying fistula type (κ=1.0, p<0.001) and number of tracts (κ=1.0, p<0.001) (Table 4). Abscess detection showed near-perfect concordance (κ=0.93, p<0.001), with 15.0% (n=9) identified on CT and 13.3% (n=8) confirmed intraoperatively. Internal opening visibility on CT showed moderate agreement (κ=0.44, p<0.001), with 13.3% (n=8) discrepancies. Measurements of internal opening distance (CT: 2.93 ± 0.99 cm vs. intraoperative: 2.96 ± 0.98 cm; p=0.779) and tract length (CT: 4.38 ± 1.64 cm vs. intraoperative: 4.36 ± 1.62 cm; p=0.138) showed no significant differences.

Table 4: Agreement in Fistula Tract Number (CT vs. Intraoperative)

Surgical Outcomes

There were no postoperative surgical site infections (SSI). The average visual analog scale (VAS) pain score was 1.35 ± 1.23, and 93.3% (n=56) experienced minimal pain. Contrast extravasation in 6.7% (n=4) of cases.

Key Figures

Figure 1: Bar chart of age distribution.

Figure 2: Distribution of Parks classification.

Figure: 3

Figure: 4

Figures 3-4: Bland-Altman plots for internal opening distance and tract length.

These findings emphasize the diagnostic accuracy of CT fistulography for preoperative planning, especially in classifying fistulae and detecting abscesses. Minor discrepancies in the visibility of the internal opening emphasize the utility of combining imaging with surgical exploration.

Fistula in ano, though a benign condition, poses significant challenges due to its chronic nature, high recurrence rates, and the potential for persistent discomfort. Its development from infected anal glands often follows an anorectal abscess, necessitating an effective surgical approach aimed at complete resolution while preserving sphincter function. The success of surgical intervention relies heavily on precise preoperative assessment, which underscores the importance of reliable imaging techniques in guiding clinical decision-making [9].

Despite the existence of multiple imaging modalities, each with its own advantages and limitations, CT fistulography has emerged as a valuable diagnostic tool for delineating the anatomy of perianal fistulas. In the present study, CT findings demonstrated a strong correlation with intraoperative observations, reinforcing its utility in preoperative planning. The demographic characteristics of the study population aligned with previous research, with the majority of patients falling within the third to fourth decade of life and a significant predominance of males. Similar trends were reported in studies by Narasimha Rao KL et al. and Qureshi IP et al., indicating that fistula in ano predominantly affects males in their middle years [10-11].

Clinically, perianal discharge was the most common presenting symptom, followed by pain, a finding consistent with earlier studies. The presence of comorbidities, particularly diabetes mellitus and hypertension, was relatively low in the study cohort, with only a small percentage of patients having underlying conditions. This differs from the findings of Ramanujam et al., who reported a high prevalence of hypertension in their study population. The variance could be attributed to demographic differences and ethnicity-based predispositions.

In terms of anatomical characteristics, the study revealed that nearly half of the patients had their external fistulous opening located posteriorly, a distribution comparable to the findings of Narasimha Rao KL et al. Notably, all patients in the study had a single external opening, which simplified classification and surgical planning. The fistula tracts were predominantly transsphincteric, with a smaller proportion being intersphincteric, aligning with the widely accepted Parks’ classification system. The mean tract length measured in the study was consistent with findings reported by Srivastava et al., further reinforcing the reliability of CT in determining the anatomical extent of fistulous tracts [12].

One of the key objectives of the study was to assess the diagnostic accuracy of CT fistulography in comparison with intraoperative findings. The results demonstrated that CT scans successfully identified 96.7% of single fistulas and 3.3% of cases with two fistulous tracts, with these findings being corroborated during surgery. This suggests that CT imaging is highly reliable in detecting the primary fistulous tract and its branches, reducing the likelihood of unexpected intraoperative findings. Previous studies, such as those conducted by Liang et al., have similarly emphasized the high accuracy of CT fistulography in delineating fistulous anatomy, particularly in complex cases where traditional methods may fall short [13].

The study also identified high concordance between the fistula location recognized on CT and intraoperative localization, with preoperative identification of 27.1% of intersphincteric fistulas and 72.9% of transsphincteric fistulas being correct. This supports the utility of CT to offer an accurate anatomical guide for surgery, reducing intraoperative uncertainty and improving surgical outcomes. The accuracy of CT imaging in detecting internal openings was also examined, revealing an 86.7% success rate in confirming single openings during surgery. However, in cases with multiple openings, the accuracy was significantly lower, which could be attributed to the inherent complexity of these fistulas, making their complete visualization challenging even with advanced imaging techniques [14].

A crucial finding of the study was the strong agreement between the internal opening distances measured on CT and intraoperatively. The mean difference between the two measurements was not statistically significant, indicating that CT fistulography provides a reliable estimation of the internal opening location. This has significant clinical implications, as precise identification of the internal opening is critical for determining the most appropriate surgical approach. The study further validated the role of CT in detecting associated abscesses, with 88.9% of CT-identified abscesses being confirmed intraoperatively. The minimal occurrence of false positives underscores the accuracy of CT in preoperative assessment, allowing surgeons to make informed decisions regarding drainage and surgical management.

While CT fistulography demonstrates high diagnostic accuracy, it is essential to acknowledge the limitations of traditional imaging techniques such as conventional fistulography. Earlier work by Kuijpers & Schulpen emphasized the limitations of fistulography, with a low detection rate of the entire length of fistulous tracts and internal openings. CT imaging is more thorough since it includes three-dimensional visualization and hence enhances diagnostic accuracy. Nevertheless, newer imaging modalities such as dynamic contrast-enhanced MRI (DCEMRI) have shown superior sensitivity and specificity in detecting secondary tracts and complex fistulas, as demonstrated by Beckingham et al. While CT remains a valuable tool, integrating MRI in cases with suspected complex fistulas could further enhance diagnostic accuracy and surgical planning [15].

The evolving landscape of fistula in ano treatment underscores the need for precise preoperative assessment to optimize surgical outcomes. While traditional procedures such as fistulotomy and seton placement remain widely practiced, the shift towards sphincter-preserving techniques highlights the necessity of accurate imaging for treatment planning. The emergence of minimally invasive procedures such as Video-Assisted Anal Fistula Treatment (VAAFT), Ligation of Intersphincteric Fistulous Tract (LIFT), and fistula plug placement has redefined the therapeutic approach, minimizing morbidity while preserving continence. The integration of advanced imaging modalities into clinical practice facilitates precise surgical decision-making, ensuring that patients receive the most appropriate intervention tailored to their fistula anatomy.

Overall, the findings of this study underscore the clinical utility of CT fistulography in the preoperative evaluation of fistula in ano. By offering a high degree of correlation with intraoperative findings, CT imaging serves as a reliable tool for delineating fistulous tracts, identifying internal openings, and detecting associated abscesses. While MRI remains the gold standard for complex fistulas, CT provides a valuable alternative in resource-limited settings where MRI may not be readily available. Subsequent studies need to emphasize developing imaging protocols and investigating the application of artificial intelligence in fistula imaging to improve diagnostic precision and surgical success further. With the utilization of advancements in technology, clinicians can optimize fistula in ano management by decreasing recurrence and enhancing the overall quality of life in affected individuals.

The present study comprehensively evaluated the accuracy of CT fistulogram in diagnosing fistula in ano and its role in guiding surgical intervention. The findings demonstrated that CT fistulography is a highly reliable imaging modality, showing near-perfect agreement with intraoperative findings in identifying the number, type, and location of fistulous tracts, as well as the presence of abscesses. With an accuracy rate of 96.7% in detecting the number of fistulae and a negligible difference in measuring internal opening distances compared to surgical findings, CT emerges as a crucial tool in preoperative planning. Its superior ability to provide detailed three-dimensional imaging enables precise delineation of complex fistulas, minimizing intraoperative surprises and optimizing surgical outcomes. Given its high sensitivity and specificity, CT fistulography proves to be a valuable diagnostic approach, particularly in cases where conventional X-ray fistulography falls short. The study underscores the importance of integrating CT fistulogram into routine clinical practice for the accurate assessment and effective management of fistula in ano, ultimately improving patient prognosis and reducing postoperative complications.

1. Ramesh PB. Anal fistula with foot extension—Treated by kshara sutra (medicated seton) therapy: A rare case report. Int J Surg Case Rep. 2013 Jan 1;4(7):573–6.
2. Dudhamal TS, Gupta SK, Bhuyan C, Singh K. The role of Apamarga Kshara in the treatment of Arsha. Ayu. 2010;31(2):232–5.
3. Salem OTA. Fistulectomy and fistulotomy for low anal fistula. Rawal Med J. 2012;37(4):409–11.
4. Zuhair Bashir K. Fistulotomy versus fistulectomy as a primary treatment of low fistula in Ano. 2012;510–5.
5. Jacob TJ, Perakath B, Keighley MRB. Surgical intervention for anorectal fistula. Cochrane Database Syst Rev. 2010 May 12;(5):CD006319.
6. Conole FD. The significance of the anal gland in the pathogenesis of anorectal abscess and fistula. Am J Proctol. 1967 Jun;18(3):232–8.
7. McColl I. The comparative anatomy and pathology of anal glands. Arris and Gale lecture delivered at the Royal College of Surgeons of England on 25th February 1965. Ann R Coll Surg Engl. 1967 Jan;40(1):36–67.
8. Shafik A. A new concept of the anatomy of the anal sphincter mechanism and the physiology of defecation. VI. The central abscess: a new clinicopathologic entity in the genesis of anorectal suppuration. Dis Colon Rectum. 1979 Aug;22(5):336–41.
9. Shafer AD, McGlone TP, Flanagan RA. Abnormal crypts of Morgagni: the cause of perianal abscess and fistula-in-ano. J Pediatr Surg. 1987 Mar;22(3):203–4.
10. de Vries PA, Friedland GW. The staged sequential development of the anus and rectum in human embryos and fetuses. J Pediatr Surg. 1974 Oct;9(5):755–69.
11. Levi AC, Borghi F, Garavoglia M. Development of the anal canal muscles. Dis Colon Rectum. 1991 Mar;34(3):262–6.
12. Fröber R, Krebs U, Haas A, Fischer MS, Schier F, Linss W. Three-dimensional reconstruction of the anal striated musculature in a human fetus. Cells Tissues Organs. 2001;169(2):152–7.
13. Kromer P, Korzeniowska-Kromer E. Anal canal development in the embryonic and early foetal period. Folia Morphol. 2003;62(3):285–7.
14. Arakawa T, Hwang SE, Kim JH, Wilting J, Rodríguez-Vázquez JF, Murakami G, et al. Fetal growth of the anal sinus and sphincters, especially in relation to anal anomalies. Int J Colorectal Dis. 2016 Mar;31(3):493–502.
15. Barleben A, Mills S. Anorectal Anatomy and Physiology. Surg Clin. 2010 Feb 1;90(1):1–15.