Levator ani muscle complex: anatomic findings in nulliparous patients at thin-section MR imaging with double opacification.

PURPOSE: To determine levator ani muscle complex anatomic findings in nulliparous patients at magnetic resonance (MR) imaging examinations performed with opacification of the vagina and rectum with ultrasonographic gel.

MATERIALS AND METHODS: The institutional review board approved this retrospective study, and the informed consent requirement was waived. Findings from pelvic MR imaging examinations with double opacification in 123 consecutive nulliparous patients (mean age, 32.13 years; age range, 17-45 years) who were suspected of having endometriosis were reviewed. The pubococcygeal muscles were analyzed on coronal sections obtained through the middle part of the vagina, perineal body, and anal canal. The puborectalis muscles were analyzed on coronal sections obtained through the perineal body. The iliococcygeal muscles were analyzed on coronal sections obtained through the rectum. Miscellaneous findings such as visibility of deep transverse muscles of the perineum, perineal body, and focal muscle defects were also noted.

RESULTS: In 56% (69 of 123) of patients, at least one morphologic variant (thinning or aplasia) of a muscle of the levator ani complex was noted. Variants of puborectalis muscles were noted in 6% of patients. Variants of iliococcygeal muscles were noted in 13%. Variants of pubococcygeal muscles were noted in 32% at the anal canal level, in 49% at the perineal body level, and in 49% at the vaginal level. Variants of pubococcygeal muscles were noted on the left side in 53 patients (77% of pubococcygeal muscle variants).

CONCLUSION: Numerous morphologic variants of the levator ani muscle complex are noted at coronal thin-section MR imaging with double opacification. Most involve the pubococcygeal muscle on the left side at perineal body and vaginal levels. Whether some of these anatomic findings may favor prolapse after vaginal birth may be questioned.