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[Ano-perineal fistula in MRI. Contribution of T2 weighted sequences]
1Service Central de radiologie, Centre Hospitalier Général, Saint-Nazaire.
Introduction:
Anal fistulae are pathological conditions observed in infections of the Hermann and Defosses' glands or related to Crohn's diseases. The success and the lack of complication of surgical treatment depends on how accurately the tracks are assessed. The contribution of MRI in anal fistulas is now well established but the imaging appearance is not well discribed. The purpose of this work was to discribe the different patterns of lesions.
Material And Methods:
Eighteen patients with anal fistulas were examined with MRI before operation (mean delay: 14 days. range: 1-56). SE T2 sequences, in coronal and axial planes referred to the anal canal were performed. The examinations were reviewed and compared with the results of surgical assessment to correlate imaging and surgical findings.
Results:
Lesions were hyperintense on T2-weighted sequences but were also iso- or poorly hyper-intense when they did not contain fluids but only inflammatory tissue. When involving the supra-levator space, lesions were nodular. They were well limited if they occurred in the supra-levator space itself. On the contrary, the rectal wall was thickened and hyper-intense when the fistulous tract reached it. Lesions were similar in Crohn's disease, except for anal fissures which were seen as a tubular hypersignal in contact with the anal lumen. On T2 sequences, healed fistulas were not visible.
Conclusion:
The simple SE T2 sequences can discriminate between different patterns of lesions, especially for supra-levator extensions, fissures in Crohn's disease and chronic inflammatory lesions without fluid. The use of more recent machines or fat suppression sequences may improve the detectability of lesions, especially the more chronic ones.
Insights
Magnetic resonance imaging (MRI) effectively characterizes anal fistula patterns, distinguishing fluid-filled tracts from inflammatory tissue. T2-weighted sequences aid in assessing supra-levator extensions and Crohn's disease-related fissures.
Area of Science:
- Radiology
- Gastroenterology
- Surgical Anatomy
Context:
- Anal fistulae are complex anorectal conditions often linked to infections or Crohn's disease.
- Accurate assessment of fistulous tracts is crucial for successful surgical outcomes.
- While MRI's utility in anal fistulae is recognized, detailed descriptions of imaging patterns are lacking.
Purpose:
- To describe the diverse imaging patterns of anal fistulae using MRI.
- To correlate MRI findings with surgical assessments for improved diagnostic accuracy.
Summary:
- Simple spin-echo (SE) T2-weighted MRI sequences effectively differentiate anal fistula patterns, including supra-levator extensions and inflammatory changes without fluid.
- Lesions appear hyperintense on T2 sequences, though iso- or poorly hyperintense when primarily inflammatory.
- In Crohn's disease, anal fissures present as tubular hypersignals; healed fistulae are typically not visible on T2 sequences.
Impact:
- Provides a descriptive framework for interpreting MRI in anal fistula cases.
- Enhances the understanding of imaging characteristics for better surgical planning and patient management.
- Suggests potential for improved lesion detectability with advanced MRI techniques like fat suppression.