ENDOSONOGRAPHY OF THE ANAL SPHINCTERS - NORMAL ANATOMY AND COMPARISONWITH MANOMETRY

To determine the normal anal anatomy in vivo, anal endosonography and manometry were performed in 93 nulliparous females, and endosonography alone in 21 healthy males. Endosonography did not reveal any plane of cleavage between the components of the external anal sphincter, thoug h a changing pattern at different levels conforming to a trilaminar ar rangement was apparent. The deep (proximal) aspect of the external sph incter was annular in 72% of females and 76% of males. The superficial external sphincter was elliptical in 76% and 86%, the subcutaneous pa rt conical in 56% and 57%, respectively. The external sphincter was sh orter anteriorly in females. Aberrant insertions from the external sph incter anteriorly were identified in 14%. The longitudinal muscle laye r could be distinguished sonographically in all males, as the external sphincter was relatively hypoechoic, but in 60% of the females the lo ngitudinal muscle and external sphincter were of similar echogenicity and sonographically indistinguishable. The subepithelial tissues and i nternal sphincter were identified in each subject. The external sphinc ter was thicker bilaterally (P = 0.001) in males (8.6 +/- 1 mm, mean /- S.D.) compared to females (7.7 +/- 1.1), which related to the highe r weight of the males (73 +/- 7 vs 65 +/- 11 kg, P < 0.0001). The mean maximum lateral thickness of the internal sphincter (1.8 +/- 0.5 vs 1 .9 +/- 0.6) and the longitudinal muscle (2.5 +/- 0.6 vs 2.9) in female s and males were not significantly different. There was no relationshi p between the manometric resting or squeeze pressures in the anal cana l, and the internal or external sphincter thickness.