Endoanal and Endorectal Ultrasonography: Methodology and Normal Anorectal Anatomy

High-resolution three-dimensional endoanal ultrasonography (3D-EAUS) clearly demonstrates the anatomy of the anal canal. All relevant structures, including the puborectalis muscle, the internal and external sphincter, the conjoined longitudinal layer, and the transverse perinei muscles, are visualized, and any sphincter disruptions or defects can be detected. The asymmetrical shape of the anal canal and the gender differences in the ventral part of the external sphincter are also easily evaluated in the different reconstructed planes of the three-dimensional volume. High-resolution three-dimensional endorectal ultrasound (3D-ERUS) provides an accurate visualization of the five-layer structure of the rectal wall and of all the pelvic organs adjacent to the rectum. The purpose of this chapter is to present the technique of 3D-EAUS and 3D-ERUS and to revise the ultrasonographic anatomy of the anorectal region.