The Role of 3D Endoanal Ultrasonography ( 3D ‐ EAUS ) in the Evaluation of Perianal Fistulae—A Retrospective Observational Study at a Tertiary Care Centre

PURPOSE: Perianal fistulae are sequelae of suppurative anal disease. Preoperative imaging provides a detailed evaluation of fistula anatomy and anal sphincter involvement. This helps in determining surgical approach and prevents complications such as recurrence and incontinence. Three-dimensional endoanal ultrasonography (3D-EAUS) has emerged as a novel technique in fistula imaging in recent times. The aim of this study was to evaluate the diagnostic utility of 3D-EAUS in perianal fistulae by identifying the preoperative imaging characteristics and their comparison with intraoperative findings. MATERIAL AND METHODS: This research employed a retrospective observational study design. It was a diagnostic validation study wherein 3D-EAUS imaging features were compared with the intraoperative surgical findings (considered as the reference standard for analysis). Medical records of patients operated for perianal fistulae over a period of 24 months from June 2023 to May 2025 were accessed from the medical records department. All the patients who underwent 3D-EAUS as part of the preoperative workup for fistula surgery were included in the study, subject to the completeness of records and availability of adequate preoperative imaging. Based on the eligibility criteria, 345 patients were selected as the study population. Demographic characteristics, ultrasonography features, and intraoperative findings were recorded. Diagnostic indices were calculated for various parameters of 3D-EAUS, followed by a comparison of 3D-EAUS features with the intraoperative findings using concordance metrics and kappa statistics. RESULTS: Demographic analysis revealed the mean age of study population was 48.9 years with a standard deviation of +/-10.7 years. There was an obvious male preponderance with 76% males as compared to 24% females. The study revealed that trans-sphincteric fistula was the most common type (57.4%) while posterior (5-7 o'clock) was the commonest position for internal opening (54.4%). 3D-EAUS showed a high sensitivity (> 85%), specificity (> 95%) and diagnostic accuracy (> 90%) for various parameters in the diagnosis of perianal fistulae. Concordance statistics indicated 88.7% concordance with intraoperative findings for primary tract identification while 95.1% patients correlated for internal opening identification. Secondary tracts were accurately delineated in 84.6% patients while 92.3% showed concordance for adjacent abscesses/collections. Kappa values suggested almost perfect agreement between 3D-EAUS and surgical findings for internal opening (k = 0.91) and adjacent abscess identification (k = 0.84) while primary and secondary tract identification showed significant agreement (k = 0.77 and k = 0.68 respectively). CONCLUSION: Comprehensive preoperative imaging of perianal fistulae ensures proper management and prevents complications. 3D-EAUS shows high sensitivity, specificity, and accuracy in the diagnosis of perianal fistulae. It overcomes the imaging limitations of 2D ultrasonography and has a diagnostic efficacy comparable to MRI fistulogram, although at a much lower cost. This makes 3D-EAUS a suitable alternative to MRI in preoperative imaging as well as in follow-up cases, especially in resource-poor settings.