Role of magnetic resonance imaging in pre-operative assessment of ano-rectal fistula

The Role of Magnetic Resonance Imaging in Pre-operative Assessment of Anorectal Fistula With Surgical Correlation

Background Anorectal fistulas are chronic inflammations of peri-anal tissues that form a connection between the perineal skin and the anal canal. Accurate preoperative evaluation of the main fistula's trajectory and pelvic tissues is essential for effective surgical treatment of anal fistulas. The inability to detect concealed lesions may result in the recurrence of fistulas and the conversion of a simple fistula into a complex fistula. Magnetic resonance imaging (MRI) imaging can detect concealed pathways and abscesses, thereby exposing the intricate connection between the fistula and anal-sphincter complex. This data serves as a roadmap for making surgical decisions, thereby reducing the likelihood of illness recurrence and complications after surgery. Aim To evaluate the role of MRI in pre-operative assessment of an anorectal fistula, compare its findings with surgical results. Materials and methods The research was conducted at the Radiology Department, Apollo Hospital, Hyderabad. It was a prospective observational study. IBM SPSS Statistics for Windows, Version 17 (released 2008; IBM Corp., Armonk, New York, United States) was utilized for data analysis. The mean and standard deviation were computed. We further applied appropriate statistical tests to determine the significance of MRI features with pre-operative findings. Results MRI accurately detects features like abscesses (sensitivity-100%, specificity-97.06%), secondary tracts of the fistula (sensitivity-93.55%, specificity-94.12%), horseshoe appearance, and supralevator extension (sensitivity-100%, specificity-97.50%, and 97.62%, respectively). Conclusion When comparing our results with intraoperative findings, MRI showed high sensitivity and specificity in detecting abscesses, secondary tracts, horseshoe appearances, and supralevator extensions. Our findings suggest that MRI can offer anatomical and pathological information for the pre-operative care and surgical planning of perianal fistulas.

Magnetic resonance imaging in the workup of patients with perianal fistulas

Background

Perianal sepsis and fistulas are common lesions. Fistula-in-ano is a tedious problem because of high recurrence rates and severe unexpected complications postoperatively. Many imaging modalities are used to evaluate this area. Magnetic resonance imaging (MRI) has been considered the gold standard procedure for perianal fistula assessment, i.e., it provides the surgeon with an accurate roadmap to select the best surgical approach, determines the extent of sphincter division, and estimates the risk of postoperative incontinence. We carried out a prospective diagnostic accuracy study involving 50 patients (mean age, 42.44 years) with perianal fistulas who underwent pelvic MRI with a 1.5 Tesla scanner using multiple sequences, including diffusion and post-contrast series that were either local or systemic. This study aimed to evaluate the diagnostic validity of pelvic MRI/MR fistulogram in perianal fistula assessment, identify perianal fistula-associated findings by MRI, and optimize the MRI technique with maximum technical safety.

Results

Intersphincteric fistulas were the most common type of perianal fistula observed based on Parks’ classification. Intersphincteric, trans-sphincteric, extrasphincteric, and suprasphincteric fistulas were found in 30 (60%), 12 (24%), 4 (8%), and 4 (8%) patients, respectively. According to St. James’ classification, 21 (42%), 9 (18%), 8 (16%), 4 (8%), and 8 (16%) patients had perianal fistula grades I, II, III, IV, and V, respectively. The combination of variable MR sequences and MR fistulogram increased the diagnostic validity of MRI examinations. Our results correlated with surgical results (reference standard) with perfect interobserver reliability.

Conclusions

Of all imaging modalities, MRI has become a prerequisite for a successful surgery of a perianal fistula. MRI can identify: (a) fistula morphological details, (b) the relationship between the fistulous tract and the anal sphincter, (c) fistula wound healing, (d) an active versus chronic scarred fistula, (e) postoperative stigmata, and (f) a perianal fistula from its mimics. MRI with variable sequences and MRI fistulogram are successful combinations that increase diagnostic efficiency with technical safety by avoiding both ionizing radiation and systemic gadolinium.

Best non-contrast magnetic resonance imaging sequence and role of intravenous contrast administration in evaluation of perianal fistula with surgical correlation

PURPOSE

To evaluate the best non-contrast magnetic resonance imaging (MRI) sequence and role of intravenous contrast administration in preoperative characterization and classification of perianal fistulae, keeping surgery as gold standard.

METHODS

This prospective study comprised of forty-five consecutive patients with actively draining external perianal opening. MRI was performed on a 1.5 T scanner using non-contrast and contrast enhanced sequences in multiple planes. St. James's University Hospital MRI based classification system was used to classify the fistulae into five grades. Taking surgery as gold standard, association between surgical and MRI findings was statistically analysed.

RESULTS

Of the 45 patients recruited, forty were deemed eligible for inclusion. Mean age was 39.7 ± 11.7 years with male preponderance (M: F = 8:1). Commonest type was Grade 1 (40%). The best sequences in terms of overall accuracy were axial & coronal planes of contrast enhanced fat suppressed (FS) T1W turbo spin echo (TSE) (95.7%) followed by FS T2W TSE (94.1%) while sagittal T2W TSE sequence with or without fat suppression had the lowest accuracy (90.13%). The difference in overall diagnostic accuracy of FS T2W TSE and contrast enhanced FS T1W TSE sequence for evaluating perianal fistula was not statistically significant (p = 0.52). However, contrast study had a better accuracy in detecting internal openings and secondary tract of recurrent/ post-operative cases.

CONCLUSION

Best non-contrast MRI sequence is FS T2W TSE (axial and coronal). Non-contrast MRI is equally efficient to contrast study while evaluating primary/previously unoperated cases thereby eliminating the role of contrast in such cases. However, intravenous contrast should be administered for evaluating post-operative cases with recurrence.