Multiplanar anal endosonography – normal anal canal anatomy

Abstract

INTRODUCTION: Volume acquisition during anal ultrasound enables multiplanar imaging of the anal canal. The normal ultrasonic multiplanar appearance of the anal canal is described and gender differences in canal anatomy are highlighted. METHODS: Ten male and 12 female normal volunteers (mean ages 31.5 years (s.d. 5.9) and 31.2 (s.d. 6.7)) had three-dimensional anal endosonography (3-D AES). Each volume dataset was seeded in the axial plane facilitating multiplanar identification of known anatomical structures. RESULTS: The anterior external anal sphincter (EAS) was significantly longer in men than women 30.1 mm (3.9) vs 16.9 mm (7.4) (P < 0.001). There was no difference in the length of the puborectalis 24.7 mm (6.4) vs 24 mm (5) (P=0.78) in men compared with women. The cranial extent of the anterior EAS was tilted forward in both sexes. The angle formed by the anterior EAS and the longitudinal axis of the anal canal was more acute in men than in women (11.1 degrees vs 18.6 degrees; P=0.007). Dataset volume seeding of familiar structures in the axial plane allowed the multiplanar endosonographic anatomy to be described. CONCLUSIONS: Multiplanar AES has enabled detailed longitudinal measurement of the components of the anal canal and has revealed important gender differences. The multiplanar ultrasonic appearance of the normal anal canal has been described for the first time.