OBJECTIVE-To describe the appearance and occurrence of abnormalities in the levator ani muscle seen on magnetic resonance imaging (MRI) in nulliparous women and in women after their first vaginal birth.METHODS-Multiplanar proton density magnetic resonance images were obtained at 0.5-cm intervals from 80 nulliparous and 160 vaginally primiparous women. These had been previously obtained in a study of stress incontinence, and half the primiparas had stress incontinence. All scans were reviewed independently by at least two examiners blinded to parity and continence status. RESULTS-Nolevator ani defects were identified in nulliparous women. Thirty-two primiparous women (20%) had a visible defect in the levator ani muscle. Defects were identified in the pubovisceral portion of the levator ani in 29 women and in the iliococcygeal portion in three women. Within the pubovisceral muscle, both unilateral and bilateral defects were found. The extent of abnormality varied from one individual to the next. Of the 32 women with defects, 23 (71%) were in the stress incontinent group.CONCLUSION-Abnormalities in the levator ani muscle are present on MRI after a vaginal delivery but are not found in nulliparas.During a study of the role of vaginal birth in causing urinary incontinence we obtained magnetic resonance images of women with stress incontinence after their first vaginal birth and of normal continent nulliparous and primiparous controls. On evaluating these scans we found abnormalities in the levator ani muscles in both the continent and incontinent women. The abnormalities seemed to occur only in women who delivered vaginally, and not in nulliparas. These abnormalities involved both the pubovisceral and iliococcygeal portions of the muscle and were sometimes unilateral and sometimes bilateral. Here we describe these defects and evaluate whether or not they are associated with vaginal delivery. MATERIALS AND METHODSMagnetic resonance images of the pelvis were obtained from 240 women as part of an institutional review board-approved study concerning vaginal delivery and stress urinary incontinence. Multiplanar two-dimensional fast spin (echo time 15 ms, repetition time 4000 ms) proton density magnetic resonance images of all pelves were obtained by use of a 1.5-tesla superconducting magnet (Signa; General Electric Medical Systems, Milwaukee, WI) with version 5.4 software as previously described. 1 Images 5 mm apart were obtained in axial, coronal, and sagittal views.

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Benefits from implementation of these guidelines include: improved diagnosis of OASIS, optimal functional outcomes following repair, and evidence-based counselling of women for future childbirth.

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