Multiplanar imaging has revealed a direct relationship between the length of a sphincter tear and its radial extent as shown on axial scanning. Marked sex differences in sphincter configuration have been demonstrated. In women the shorter anterior sphincter length highlights the risk of complete sphincter disruption with extensive tears.

A coordinated response by the internal anal sphincter to rectal distention with recovery of anal pressure from the distal to the proximal sphincter is suggested. Continence may rely on the character of internal anal sphincter inhibition, and recovery and preoperative assessment of rectoanal inhibitory reflex parameters may be important for predicting functional result following low anastomosis.

The limits of agreement for intraobserver and interobserver measurements of anal canal structures on AES have been defined. Interobserver assessment of sphincter disruption is very good.