Effect of vaginal delivery and ageing on the anatomy of the female anal canal assessed by three-dimensional anorectal ultrasound

Aim The effect of vaginal delivery and ageing on the anatomy of the anal canal was assessed using three-dimensional anorectal ultrasound to determine the interobserver reliability. Method One-hundred and eighteen asymptomatic women without sphincter damage were grouped according to parity and mode of delivery. They were then stratified by age (=50 years vs >50 years). Group I consisted of 35 nulliparous women, of mean ages 36 years (n = 20) and 62 years (n = 15), Group II consisted of multiparous women, having one or more vaginal deliveries (n = 43), of mean ages 43 years (n = 20) and 60 years (n = 23) and Group III consisted of women who had a Caesarean section (n = 40) of mean ages 41 years (n = 20) and 56 years (n = 20). The groups were compared with regard to the length and the thickness of the external anal sphincter, the internal anal sphincter, the posterior external sphincter and the puborectalis in all quadrants and the anterior gap. Interobserver variability was assessed. Results In women having vaginal delivery the length of the anterior external sphincter was shorter (P = 0.0004) and the gap was longer (P = 0.0306). The external sphincter tended to be thinner in individuals having vaginal delivery (P = 0.0677) and in those subjects over 50 years of age having had a vaginal delivery (P = 0.0164). In nulliparous women, the internal sphincter was thicker in subjects over 50 years of age (P = 0.0229). The intraclass correlation coefficient was 0.7550.916 for sphincter muscle and gap length and 0.4460.769 for muscle thickness. Conclusion Vaginal delivery was associated with a shorter anterior external sphincter, a longer gap and a thinner anterior external sphincter in asymptomatic women. Age was correlated with sphincter thickness, and nulliparous women >50 years of age had a thicker internal sphincter. Three-dimensional ultrasound was found to be a reliable method for measuring anal structures.