Origin and insertion points involved in levator ani muscle defects

Abstract

Objective: This project sought to identify and to describe the anatomical connections affected by levator ani defects involving the pubovisceral portion of the muscle.

Study design: Fourteen magnetic resonance scans of women with unilateral levator defects were selected. The missing muscle mapping technique was used to characterize the absent muscle. Normal muscle was visualized and compared with the contralateral side. Using a three-dimensional slicer, the outline of the intact muscle was traced; models of this muscle and surrounding structures were generated.

Results: The missing muscle originates from the posterior pubic bone and extends laterally over the obturator internus muscle; it inserts into the vaginal wall, perineal body, and the intersphincteric space. Architectural distortion, with an asymmetric lateral spilling of the vagina was present in 50% of women. The defect was right sided in 71% of patients.

Conclusion: The origin and insertion points of the damaged portion of the levator ani muscle were identified.

FIGURE 1. Exemplary axial MRI with unilateral defect

Axial MR scans of an exemplary 42-year-old female with a right-sided complete unilateral levator defect are shown. The intact levator ani muscle is traced (dashed line, labeled LA). The missing muscle is denoted (asterisk). Each panel is labeled with a number indicating the level of scan in centimeters relative to the arcuate pubic ligament; positive numbers indicate slices cephalad to the ligament. EAS, external anal sphincter; R, rectum; U, urethra; V, vagina. Printed with permission from John O. L. DeLancey, MD.

FIGURE 2. Three-dimensional model of the pelvis

Three-dimensional model generated from the axial MR scans shown in Figure 1. A, and B, Oblique right and left inferolateral views, similar to the dorsal lithotomy position, are shown. In these panels the pubic bone is semitransparent and the obturator internus muscle is not shown. C, and D, Oblique right and left views peering over the pubic bone and down to the pelvic floor are shown. The urethra, vagina, and rectum have been truncated so as not to obscure the views of the levator muscles. EAS, external anal sphincter; LA, levator ani; MM, mirror image of the missing muscle; P, pubis; PB, perineal body; U, urethra; V, vagina. The missing muscle in A and D is denoted (asterisk). Printed with permission from John O. L. DeLancey, MD.

FIGURE 3. Axial MRI showing loss of attachment

Axial MR scan of a 46-year-old multiparous woman is shown. The intact attachment between the left pubovisceral muscle and the vaginal wall is indicated (white arrowhead), the loss of this attachment is shown on the right side (missing muscle; black arrowhead). The insertion of the intact pubovisceral muscle into the perineal body (PB) is shown (white arrow); the loss of this attachment on the contralateral side is also shown (black arrow). R, rectum; U, urethra; V, vagina. Printed with permission from John O. L. DeLancey, MD.

FIGURE 4. Four examples of unilater levator defects

Axial MR scans of 4 different women with complete unilateral levator defects are shown. Note the variations in morphology. The intact levator ani muscle is traced (dashed line) and labeled LA. The missing muscle is denoted (asterisk). A, B, and C, the defect is shown on the right side and D, on the left side. EAS, external anal sphincter; P, pubis; R, rectum; U, urethra; V, vagina. Printed with permission from John O. L. DeLancey, MD.