Changes in Anorectal Morphologic and Functional Parameters After Fistula-in-Ano Surgery

PURPOSE: This study aimed to analyze changes in anal continence and morphologic and functional anorectal variables after fistula-in-ano surgery in a patient series with a high rate of complex fistulas. METHODS: One hundred twenty patients with a mean age of 46.9 (standard deviation, 12.8) years were prospectively analyzed by evaluating anal continence, results of endoanal ultrasound examination and anorectal manometry, and pudendal nerve terminal motor latency before and after fistula-in-ano surgery. RESULTS: Forty-three patients (35.8%) were referred for recurrent fistulas; fistulas in and 70 (58.3%) were considered complex. Preoperatively, 17 patients (14.2%) presented with impaired continence. At follow-up, 59 patients (49.2%) had some degree of incontinence (P < 0.001). The techniques that most affected continence were rectal advancement flap and fistulotomy. Endoanal ultrasound examination showed that the number of patients with internal anal sphincter defects increased from 37 (30.8%) to 78 (74.3%) after surgery (P < 0.001); those with external anal sphincter defects increased from 17 (15.9%) to 34 (32.4%) (P < 0.001). Techniques most associated with increases in internal anal sphincter defects were fistulotomy (P < 0.003) and rectal advancement flap (P < 0.004). Anal manometry showed significant decreases in maximal resting pressure and maximum squeeze pressure in patients with previous incontinence (P < 0.001), and in those with internal anal sphincter defects (P < 0.001). Fistulotomy decreased both resting pressure (P < 0.004) and squeeze pressure (P < 0.007), whereas rectal advancement flap significantly reduced only resting pressure. Pudendal nerve latency did not differentiate continent and incontinent patients, and showed no postoperative change. CONCLUSIONS: Anal continence is significantly affected after fistula-in-ano surgery, mainly because of sphincteric lesions that affect anal canal pressures and that can be imaged with endoanal ultrasound. It is important to preoperatively recognize sphincter defects to allow adequate surgical treatment.