Defining the histopathological changes induced by nonablative radiofrequency treatment of faecal incontinence – a blinded assessment in an animal model

Abstract Aim Nonablative radiofrequency ( RF ) sphincter remodelling has been used to treat gastro‐oesophageal reflux disease ( GERD ) and faecal incontinence ( FI ). Its mechanism of action is unclear. We aimed to investigate the histomorphological and pathophysiological changes to the internal and external anal sphincter ( IAS and EAS ) following RF remodelling. Method An experimental FI model was created in 12 female pigs: eight underwent RF 6 weeks following induction of FI ( FI + RF ) and four were untreated ( UFI ). Four animals served as controls ( CG ). Two blinded pathologists examined all haematoxylin and eosin and trichrome stained slides. Results Compared with the UFI group, histological examination of the IAS in the FI + RF group demonstrated an increased smooth muscle ( SM )/connective tissue ratio (77.2 vs 68.1%, P < 0.05) and increased collagen I compared with collagen III content (67.2 vs 54.9%, P < 0.001). The RF + FI group exhibited greater SM bundle thickness compared with the UFI group ( SM width 486.93 vs 338.59 μm, P < 0.01; height 4384.4 vs 3321.0 μm, P < 0.05). The EAS of the FI + RF animals showed a significantly higher type I/ II fibre ratio (33.5 vs 25.2%, P = 0.023) and fibre type I diameter (67.2 vs 59.7 μm, P < 0.001) compared with the UFI group. Post‐ RF manometry showed higher basal (18.8 vs 0 mmHg, P < 0.001) and squeeze (76.8 vs 12.4 mmHg, P < 0.05) anal pressures. After RF treatment, the number of interstitial cells of Cajal was significantly reduced compared with the UFI and CG groups [0.9 ( FI + RF ) vs 6.7 ( UFI ) vs 0.7 ( CG ) per mm 2 , P < 0.001]. Conclusion In an animal model nonablative RF appeared to induce morphological changes in the IAS and EAS leading to an anatomical state reminiscent of normal sphincter structure.