Magnetic resonance imaging of the levator ani with anatomic correlation

OBJECTIVE: To define in women the anatomy of the levator ani muscle visible on magnetic resonance imaging (MRI) so these muscles can be studied in women with prolapse or incontinence. METHODS: Multiplanar T1- and T2-weighted MRI was obtained of two female pelvic cadaver specimens, ages 25 and 33. One specimen was hemisected, with half sectioned in the axial plane and the other half in the coronal plane. The other specimen was sectioned in the coronal plane. Anatomic cross sections of these specimens were correlated with the cadaver MRI and MRI of living patients. One sagittal and two axial series of anatomic sections not imaged were also used for comparison. RESULTS: Serial sagittal and axial MRI demonstrates the pubovisceralis ("pubococcygeus") muscle as it originates from the pubic bone, passes alongside the urethra, vagina, and rectum, and then dorsal to the anorectum. Its muscle bulk, attachment to the distal half of the vagina, and insertion between the internal and external anal sphincters can be seen on axial views. The origin of the iliococcygeus muscle at the arcus tendineus levator ani is seen in axial and coronal images. Coronal and sagittal images demonstrate the relative thickness and medial position of the pubovisceralis muscle compared with the thin, diaphragm-like lateral iliococcygeus muscle. CONCLUSION: Magnetic resonance imaging of the cadaver pelvis demonstrates the detailed anatomy of the levator ani muscle. This is an important precursor to future research of the structure, bulk, and orientation of the levator ani in living women with prolapse.