Table 1.

Characteristic Magnetic Resonance Features of the External Anal Sphincter

	Axial (Fig. 3)	Coronal (Fig. 4)	Sagittal (Fig. 5)
EAS-M	Ventrally, crosses midline distinct from SQ-EAS (Fig 3, panels -0.5 and 0).	Dorsally, crosses midline-distinct from SQ-EAS (Fig 4, panels -6.0, -6.5, -7.0) separated by ESS.	Fiber direction oblique to horizontal and vertical axes (Fig 5, panel right 1.0)
EAS-W	Extends laterally, diverging from the midline (Fig 3, panels -2.0, -1.5, -1.0)	Not possible to distinguish	Not possible to distinguish
	Distinct from PRM separated by visible gap (Fig 3, panels -2.0 and -1.5)
SQ-EAS	Ventrally, crosses midline distinct from EAS-M (0.5, 0, -0.5)	Dorsally, crosses midline distinct from EAS-M (Fig 4, panels -6.5 and -7.0)	Distinct semicircle structure on parasagittal (Fig 5, panels right 0.5 to left 0.5).
	Adjacent to anal skin (Fig 3, panels -2.5 to -1.0)	Adjacent to anal skin (Fig 4, panels -6.5 to -7.5)

EAS-M, main portion of external anal sphincter; SQ-EAS, subcutaneous external anal sphincter; ESS, external sphincter space; EAS-W, winged portion of EAS; PRM, puborectalis muscle.