Anatomy of the external anal sphincter

Abstract

The anatomy fo the external anal sphincter has been studied in 48 adult cadaveric and surgical specimens by anatomical dissection and histological sections in three-dimensional planes. The bilaminar and trilaminar concepts of external anal sphincteric anatomy are reviewed. The significant anatomical differences in the anterior portion of the external sphincter compared with the lateral and posterior portion are emphasized. The different configuration of the anterior part of the external sphincter in men and women is described. A new terminology is proposed, ‘superficial compartment’ (subcutaneous and superficial) and ‘deep compartment’ (deep and puborectalis), on the basis of the close anatomical relationship between each of these two pairs of muscles.