Correlation of the Anatomy of the Intersphincteric Anal Fistula with Sex: An Analysis through Anorectal Three-Dimensional Ultrasound

Introduction Anal fistula surgery is often associated with continence disorders due to transection of the anal sphincter muscles. A comprehensive understanding of the anatomy of the anal canal and fistula can help prevent this outcome. Objective To correlate the anatomy of the intersphincteric anal fistula with the patient's sex using three-dimensional endoanal ultrasound (3D-EAUS). Materials and Methods The present is a retrospective observational study, involving an analysis of the medical records of patients seen at the Coloproctology Service of a Public Tertiary Hospital in the state of Maranhão, Brazil, from July 2016 to December 2022. Patients were categorized by sex and assessed for the position of the internal opening (IO), distance from the IO to the anal margin, and amount and percentage of internal anal sphincter (IAS) muscle compromised by the fistulous tract. Results Intersphincteric fistulae were more common in men. The average age among men was of 46.46 years, and, among women, it was of 38.17 years. There was a difference between the sexes in terms of the duration of compromised IAS, which was longer among men. The percentage of compromised IAS was higher in males. The IO was located at a greater distance from the anal margin in male patients compared to female ones. Conclusion Male patients with intersphincteric anal fistula had the internal fistulous opening positioned more distant from the anal margin, with a greater length and percentage of the IAS muscle compromised by the fistulous tract compared to female patients with the same condition.