A Novel MRI and Clinical-Based Scoring System to Assess Post-Surgery Healing and to Predict Long-Term Healing in Cryptoglandular Anal Fistulas

Abstract

Background: Anal fistulas cause great uncertainty and anxiety in patients and surgeons alike. This is largely because of the inability to accurately confirm postoperative fistula healing, especially long-term healing. There is no scoring system available that can objectively assess cryptoglandular anal fistulas for postoperative healing and can also accurately predict long-term healing.

Methods: Several parameters that could indicate anal fistula healing were assessed. Out of these, six parameters (four MRI-based and two clinical) were finalized, and a weighted score was given to each parameter. A novel scoring system (NSS) was developed. A minimum possible score (zero) indicated complete healing whereas the maximum weighted score (n = 20) indicated confirmed non-healing. Scoring was done with postoperative MRI (at least 3 months post-surgery), then compared with the actual healing status, and subsequently correlated with the final long-term clinical outcome.

Results: The NSS was validated in 183 operated cryptoglandular fistula-in-ano patients over a 3-year period in whom 283 MRIs (preoperative plus postoperative) were performed. The postoperative follow-up was 12-48 months (median-30 months). The NSS was found to have a very high positive predictive value (98.2%) and moderately high negative predictive value (83.7%) for long-term fistula healing. Additionally, its sensitivity and specificity in predicting healing were 93.9% and 94.7%, respectively.

Conclusion: Thus, this new scoring system is highly accurate and would be a useful tool for surgeons and radiologists managing anal fistulas. By objectivizing the assessment of postoperative healing, it can both ease and streamline management. Moreover, reliable prediction of recurrence-free long-term healing will greatly allay the apprehensions associated with this dreaded disease.

Keywords: MRI; anal fistula; healing; internal opening; postoperative; scoring system.

Figure 1

Flowchart of the study.

Figure 2

A 45-year-old male patient with a right-sided high transsphincteric fistula. MRI done 12 weeks after surgery showed complete healing. He had a weighted score of zero as per the new scoring system (NSS). The patient is asymptomatic at follow-up of 38 months. (A) Axial section (schematic diagram); (B) coronal section (schematic diagram); (C) pre-operative axial T2-weighted MRI showing high tract at 7 o’clock; (D) sketch of figure (C) highlighting high tract at 7 o’clock (green color); (E) pre-operative coronal T2 weighted MRI showing high tract of right side; (F) sketch of figure-(E) highlighting high transsphincteric tract on right side (green color); (G) post-operative axial T2-weighted MRI showing healed fistula at 3 months; (H) sketch of figure-(G); (I) post-operative coronal T2-weighted MRI showing healed fistula; (J) sketch of figure-(I).

Figure 3

A 32-year-old male patient with a posterior high transsphincteric fistula. MRI done 16 weeks after surgery showed complete healing. He had a weighted score of zero as per the new scoring system (NSS). The patient is asymptomatic after a follow-up of 30 months. (A) Axial section (schematic diagram); (B) Coronal section (schematic diagram); (C) Pre-operative axial T2-weighted MRI showing high tract on right side; (D) Sketch of figure-(C) highlighting high tract on right side (green color); (E) Pre-operative axial STIR MRI; (F) Post-operative axial T2-weighted MRI showing healed fistula at 4 months; (G) Sketch of figure (F); (H) Post-operative axial STIR MRI showing healed fistula. STIR: Short-T1 Inversion Recovery.

Figure 4

A 31-year-old female patient with a right-sided high transsphincteric recurrent fistulas and abscess. MRI done 20 weeks after surgery showed complete healing. She had a weighted score of three as per the new scoring system (NSS). The patient had a recurrence of fistula after 18 months. (A) Axial section (schematic diagram); (B) Coronal section (schematic diagram); (C) Pre-operative axial T2-weighted MRI showing right-sided abscess; (D) Sketch of figure-(C) highlighting right-sided abscess (green color); (E) Pre-operative coronal T-2 weighted MRI; (F) Sketch of figure-(E) highlighting abscess on right side (green color); (G) Post-operative axial T2-weighted MRI showing healed fistula at 5 months; (H) Sketch of figure-(G); (I) Post-operative coronal T2-weighted MRI showing healed fistula; (J) Sketch of figure-(I); (K) Post-operative axial T2-weighted MRI showing recurrence of fistula at the same site after 18 months; (L) Sketch of figure-(K); (M) Post-operative coronal T2-weighted MRI showing recurrence of fistula at 18 months; (N) Sketch of figure (M).

Figure 5

A 67-year-old male patient with a recurrent high transsphincteric horseshoe fistula. MRI done 4 months after surgery showed incomplete healing with a weighted score of 10 as per the new scoring system (NSS). The patient’s fistula healed, confirmed by MRI done at 7 months. The patient is asymptomatic after a follow-up of 30 months. (A) Axial section (schematic diagram); (B) Coronal section (schematic diagram); (C) Pre-operative axial T2-weighted MRI; (D) Sketch of figure-(C) (fistula shown in green color); (E) Pre-operative coronal T-2 weighted MRI; (F) Post-operative axial T2-weighted MRI showing fistula not healed at 4 months; (G) Sketch of Figure 5 (fistula shown in green color); (H) Post-operative coronal T2-weighted MRI showing fistula not healed at 4 months after surgery; (I) Post-operative axial T2-weighted MRI showing fistula healed 8 months after surgery; (J) Sketch of figure-(I); (K) Post-operative coronal T2-weighted MRI showing fistula healed 8 months after surgery.

Figure 6

A 37-year-old male patient with a recurrent high transsphincteric fistula. MRI done 3 months after surgery showed incomplete healing with a weighted score of 9 as per the new scoring system (NSS). MRI done 7 months after surgery showed incomplete healing with a weighted score of 8. The healing was slow but progressive as can be made out from sequential MRIs at 3 and 7 months. Therefore, the patient was kept under observation and the fistula healed completely 9 months after surgery. The patient is asymptomatic after a follow-up of 39 months. (A) Axial section (schematic diagram); (B) coronal section (schematic diagram); (C) pre-operative axial T2-weighted MRI; (D) sketch of figure-(C) (fistula shown in green color); (E) pre-operative axial STIR MRI; (F) post-operative axial T2-weighted MRI showing fistula not healed at 3 months; (G) sketch of figure-(F) (fistula shown in green color); (H) post-operative axial STIR MRI showing fistula not healed at 3 months after surgery; (I) post-operative axial T2-weighted MRI showing fistula much smaller but still not healed 7 months after surgery; (J) sketch of figure-(I); (K) post-operative axial STIR MRI showing fistula not healed 7 months after surgery.