A Study Comparing Transperineal Ultrasound, Magnetic Resonance Imaging, Endoscopic Ultrasound, and Examination Under Anesthesia to Detect and Classify Perianal Fistulas in Patients With Crohn's Disease or Fistulas of Unknown Cause

The goal of this study is to learn how well different imaging tests detect and describe perianal fistulas in adults with Crohn's disease or fistulas with no known cause (cryptogenic). Perianal fistulas are painful tunnels that form near the anus and can lead to discharge, swelling, or infection. The main questions this study aims to answer are: How accurate is transperineal ultrasound (TPUS) compared to magnetic resonance imaging (MRI) in finding fistulas? How well do these tests identify key features like internal openings and abscesses? Do the test results help doctors make better treatment decisions? Researchers will compare TPUS and MRI to two other imaging methods: Endoscopic ultrasound (EUS), which uses a small camera and ultrasound inside the rectum Examination under anesthesia (EUA), in which a surgeon checks the area while the participant is asleep All participants will: Be adults between the ages of 18 and 75 Have a suspected or confirmed perianal fistula Be able to complete all four tests-TPUS, MRI, EUS, and EUA-within 10 days Participants will not receive any experimental treatments. The tests are part of routine care and will be done using advanced equipment by expert doctors. Each test result will be used to compare how accurate and useful the test is in real-life diagnosis and treatment planning. This study may help make fistula diagnosis faster, safer, and more affordable-especially in settings where access to MRI or surgery is limited. It may also support the use of TPUS as a first step in evaluating perianal fistulas in people with Crohn's disease.