External anal sphincter atrophy on endoanal magnetic resonance imaging adversely affects continence after sphincteroplasty

Background: There is still considerable debate about the value of preoperative anorectal physiological parameters in predicting the clinical outcome after sphincteroplasty. Recently it has been reported that atrophy of the external anal sphincter can be clearly shown with endoanal magnetic resonance imaging (MRI). The aims of this study were to investigate the prevalence of external anal sphincter atrophy in women with anterior sphincter defects due to obstetric injury and to determine the impact of external anal sphincter atrophy on the outcome of sphincteroplasty. Methods: In this prospective study, 20 consecutive women (median age 50 (range 28-75)years) with faecal incontinence due to obstetric trauma were assessed before operation with endoanal ultrasonography and endoanal MRI. The external anal sphincter was examined and evaluated for the presence of atrophy. The clinical outcome of sphincteroplasty was interpreted without knowledge of the magnetic resonance and ultrasonogaphic images. Results: In all patients anterior sphincter defects could be demonstrated with ultrasonography and MRI. External anal sphincter atrophy could only be demonstrated on MRI. Eight of 20 patients had external anal sphincter atrophy. Continence was restored in 13 patients. Outcome was significantly better in those without external anal sphincter atrophy (11 of 12 patients versus two of eight; P = 0.004). Conclusion: External anal sphincter atrophy can only be visualized on endoanal MRI and affects continence after sphincteroplasty. Endoanal MRI is valuable in the preoperative assessment of patients with faecal incontinence.