[Anal endosonography: the study technic and the correlations between the normal and echographic anatomy].

The authors report on 16 healthy volunteers examined with anal endosonography. The US examinations were performed with a dedicated Bruel and Kjaer 1846 unit equipped with a 7-MHz probe (type 1850) with 360 degrees circular mechanic movement. A rigid plastic cone filled of degassed water is mounted on the probe to ensure the symmetrical representation of the anal canal. A condom with gel on both the internal and the external surfaces is put on the cone. The peculiar anatomy of the single layers which form the anal canal determines their different US patterns. Endosonography was performed on three levels, i.e., deep, intermediate and superficial planes. In the deep plane (at the anorectal junction) anal endosonography demonstrates: epithelial-subepithelial complex (intermediate echogenicity); internal sphincter muscle (low echogenicity), made of smooth muscular fibers; longitudinal muscle (intermediate echogenicity), made of smooth and striated muscular fibers; puborectal muscle (high echogenicity), made of striated muscular fibers, and perineal body, which has a longitudinal shape in men and a transverse shape in women. In the intermediate plane anal endosonography demonstrates: epithelial-subepithelial complex, internal sphincter muscle, longitudinal muscle, and external sphincter muscle (high echogenicity), made of striated muscular fibers. In the superficial plane (distal anal canal extremity), anal endosonography demonstrates: epithelial-subepithelial complex and external sphincter muscle. Internal sphincter muscle thickness was measured and the results follow: while the average thickness was 2.1 mm, we had 1.8 mm in 12 patients under 44 and 2.6 mm in 4 patients over 44 years old. This finding is in agreement with literature data. External sphincter muscle thickness did not vary significantly in the two groups.