DIAGNOSTIC ACCURACY OF TRANSPERINEAL ULTRASONOGRAPHY FOR DETECTING PERIANAL FISTULAS KEEPING MRI FISTULOGRAM AS GOLD STANDARD

Abstract

Background: Perianal fistula is a standard anorectal complication, which is characterized by a high morbidity and recurrence rates, and requires proper imaging of the patient to manage it effectively. Magnetic resonance imaging (MRI) is the gold standard of evaluation but it is prohibitively expensive and not widely available in most settings, which limits its use. Transperineal ultrasonography (TPUS) is an appealing diagnostic tool, a non-invasive, cost-effective, alternative with potential.

Aim: To determine the diagnostic accuracy of transperineal ultrasonography in detecting perianal fistulas using MRI fistulogram as the gold standard.

Methods: This cross-sectional validation study was carried out in the Radiology Department of Mayo Hospital, Lahore, between december, 2025 and april, 2026, involving 166 patients who took part, with non-probability consecutive sampling. All patients received TPUS and then MRI fistulography. Diagnostic accuracy parameters such as sensitivity, specificity, positive predictive value, negative predictive value and the overall accuracy were determined by utilizing a 2 x 2 contingency table. Independent t-tests were used to make quantitative comparisons and chi-square tests were used to make categorical comparisons. The analysis of ROC curves was performed to determine the performance diagnostic.

Results: The mean age was 42.6 ± 11.8 years, with male predominance (67.5%). TPUS demonstrated a sensitivity of 91.2%, specificity of 72.7%, positive predictive value of 95.1%, negative predictive value of 58.8%, and overall diagnostic accuracy of 88.0%. The AUC was 0.92 (95% CI: 0.88–0.96), indicating excellent diagnostic performance. No statistically significant difference was observed between TPUS and MRI in measuring fistula length (p=0.412) and distance from anal verge (p=0.538). Detection rates of fistula (85.5% vs. 89.2%), abscess (34.9% vs. 38.0%), and rectal involvement (29.5% vs. 32.5%) were comparable between TPUS and MRI.

Conclusion: Transperineal ultrasonography as an imaging modality has been proven to be highly accurate, reliable, and accessible in diagnosing perianal fistulas with excellent agreement with MRI. It is suitable to use as a primary diagnostic measure especially in settings with limited resources.