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.
Adults between 18 and 75 years of age
Clinical suspicion or diagnosis of perianal fistula
Fistula etiology can be Crohn's disease or cryptogenic/tubercular (non-Crohn's)
Ability to undergo all four imaging procedures (TPUS, MRI, EUS, and EUA) within a 10-day period
Known or suspected anorectal malignancy
Pregnancy or breastfeeding
MRI (e.g., presence of metal implants or claustrophobia)
EUS (e.g., severe anal stenosis or intolerance to procedure)
Single group
Transperineal Ultrasound (TPUS)
Diagnostic testParticipants will undergo TPUS using a high-frequency linear and microconvex probe to evaluate fistula tracts, internal openings, and abscesses.
Magnetic Resonance Imaging (MRI)
Diagnostic testMRI of the pelvis will be performed using standardized T2-weighted, STIR, and post-contrast sequences for anatomical characterization of fistulas.
Endoscopic Ultrasound (EUS)
Diagnostic testEUS of the anorectal canal will be performed using a linear echoendoscope to visualize internal openings, fistula tracts, and perirectal collections. EUS serves as the reference standard.
Examination Under Anesthesia (EUA)
Diagnostic testParticipants will undergo EUA by a colorectal surgeon to probe fistula tracts and identify internal openings. EUA serves as the gold standard comparator.
Per-lesion sensitivity of transperineal ultrasound (TPUS) and magnetic resonance imaging (MRI) for detecting perianal fistulas
To determine and compare the diagnostic sensitivity of TPUS and MRI for identifying individual fistulous tracts, using endoscopic ultrasound (EUS) as the reference standard and examination under anesthesia (EUA) as the gold standard.
Sensitivity of TPUS vs MRI for detecting internal openings
Compare how well TPUS and MRI detect internal openings of perianal fistulas, using EUS and EUA as benchmarks.
Classification accuracy (Parks criteria) of transperineal ultrasound (TPUS) versus magnetic resonance imaging (MRI)
Compare the ability of TPUS and MRI to correctly classify fistulas using the Parks classification system, compared to examination under anaesthesia (EUA).
Sensitivity of transperineal ultrasound (TPUS) vs magnetic resonance imaging (MRI) for detecting perianal abscesses
Evaluate the ability of TPUS and MRI to detect perianal abscesses compared with endoscopic ultrasound (EUS) and examinaion under anaesthesia (EUA).
Impact on clinical management based on imaging modality
Proportion of participants whose treatment plan was changed after magnetic resonance imaging (MRI) vs after transperineal ultrasound (TPUS).
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