Unraveling the Causes of Perianal Itching: Magnetic Resonance Imaging as a Diagnostic Tool for Perianal Fistulas and Its Mimics.

Abstract

Background: Perianal itching is a common complaint associated with a variety of anorectal conditions such as fistulas, abscesses, hemorrhoids and pilonidal disease. Accurate diagnosis is essential for effective treatment and magnetic resonance imaging (MRI) plays a pivotal role due to its excellent soft-tissue resolution and multiplanar imaging.

Objective: The objective of this study was to evaluate the diagnostic utility of MRI in patients with perianal itching, focusing on the identification and classification of perianal fistulas and their mimics, using St. James and Parks classification systems.

Materials and methods: This prospective observational study was conducted in the department of radiodiagnosis over 6 months (December 2023-May 2024) and included 59 patients aged ≥ 18 years with perianal itching. MRI (1.5T) pelvis scans were obtained using T1, T2, short tau inversion recovery, diffusion-weighted imaging, apparent diffusion coefficient and postcontrast sequences. Fistulas were classified using the St. James and Parks systems. Chi-square test assessed the correlation between the classifications.

Results: Among 59 cases, perianal fistula was most common (57.6%), followed by abscess (33.9%), pilonidal sinus (5.1%) and hemorrhoids (3.4%). The mean age was 45.8 ± 10.6 years with male predominance. Grade 2 fistulas ( 47.06%) and intersphincteric type (64.70%) were most frequent. A strong correlation (P < 0.001) was observed between St. James and Parks classifications. Common complications included abscesses (70.6%) and horseshoe tracts (14.7%). MRI findings showed high concordance with clinical and surgical data.

Conclusion: MRI is a sensitive, noninvasive tool for evaluating perianal itching. It effectively characterizes underlying pathology, guides treatment planning, shows strong classification correlation and enhancing clinical decision-making.