Poster 7: Asymmetry of the Proximal and Distal Anal Canal

Abstract

OBJECTIVE: The purpose of our study was to evaluate the anatomy and functional symmetry of the anal canal. METHODS: Seventeen asymptomatic nulliparous women were studied using simultaneous 3-dimensional ultrasound imaging and manometry of the anal canal. Ultrasound imaging of the anal canal was performed transvaginally and pressures were recorded with a side-hole manometry catheter using a rapid pullthrough technique (motor-driven puller, speed 8 mm/s) at rest and during squeeze. RESULTS: The internal anal sphincter (IAS), external anal sphincter (EAS), and puborectalis muscle (PRM) are clearly visualized in the ultrasound images. The proximal zone is made up of the IAS and the PRM and the distal zone of the IAS and EAS. The rapid pullthrough technique shows a consistent double hump (proximal and distal) in the pressure profile at rest and during squeeze. Voluntary squeeze increased the mean maximum proximal pressure from 33 ± 4 mm Hg to 47 ± 4 mm Hg and increased the mean maximum distal pressure from 98 ± 8 mm Hg to 121 ± 9 mm Hg. The maximum resting and squeeze pressures in the proximal anal canal show marked circumferential asymmetry with the highest pressures in the posterior direction (P<0.05 as compared with anterior and right) and the lowest pressures in the anterior direction (P<0.05 compared with posterior, left, and right). Maximum pressures in the distal anal canal are more symmetric. CONCLUSIONS: Proximal anal canal pressures exhibit circumferential asymmetry, possibly as a result of the U-shaped anatomic structure of the PRM.FIGURE 1