Pelvic floor images: anatomy of the levator ani muscle.

PURPOSE: The levator ani has been divided into many functional portions based on necropic observation. Our objective was to use a combination of CT and magnetic resonance images to show a complete levator ani.

METHODS: Normal magnetic resonance images of the pelvis were obtained at rest in 22 volunteers while in the lying position (10 males, aged 21-23 yr). The pelvic floor images of ten cadavers (5 males) were obtained while in the supine position by CT. Source magnetic resonance images were used to measure the heights of the transverse portion of the levator ani and the area of the genital hiatus. Source magnetic resonance images and CT reconstructed images were used to study the anatomy of the levator ani.

RESULTS: The levator ani had a transverse portion and a vertical portion. The anterior transverse portion was found to be basin-shaped, the middle transverse portion was funnel-shaped, and the posterior transverse portion was dome-shaped. The transverse portion sloped sharply downward to form the vertical portion at the puborectalis plane. The vertical portion was a muscular tube outside the intrahiatal structures. The puborectalis was a u-shaped muscle outside the vertical portion. One case of the deep transverse perineal muscle was found in 22 volunteers. The volume of the ischioanal fossa influenced the anatomic appearance of the pelvic floor in cadavers.

CONCLUSIONS: The transverse portion of the levator ani has five kinds of shapes in the different-coronal sections of the pelvis, which changes from basin to dome in a lying position. The puborectalis is outside the vertical portion and not part of the levator ani.