Purpose: To quantify the longitudinal division of the internal anal sphincter (IAS) and external anal sphincter (EAS) after fistulotomy using three-dimensional endoanal ultrasound (3D-EAUS) and correlate the results with postoperative faecal incontinence.
Methods: A prospective, consecutive study was performed from December 2008 to October 2010. All patients underwent 3D-EAUS before and 8 weeks after surgery. Thirty-six patients with simple perianal fistula were included. Patients with an intersphincteric or low transphincteric fistula (<66% sphincter involved) without risk factors for incontinence underwent fistulotomy. The outcome measures were the longitudinal extent of division of the IAS and EAS in relation to total sphincter length and continence (Jorge and Wexner scores).
Results: One-year follow-up revealed a 0% recurrence rate. There was a strong correlation between preoperative 3D-EAUS measurement of fistula height with intraoperative and postoperative 3D-EAUS measurement of IAS and EAS division (p < 0.001). The relationship between the level of EAS division and faecal incontinence showed a significant difference in incontinence rates between fistulotomies limited to the lower two thirds of the EAS and those above this level. Five patients (13.9%) had worse anal continence after surgery, although this was mild in all patients (<3/20 Jorge and Wexner scale). There was no significant difference in continence scores before and after surgery (p > 0.05).
Conclusions: In patients without risk factors, division of the EAS during fistulotomy limited to the lower two thirds of the EAS is associated with excellent continence and cure rates.