Anal Sphincter Imaging of Obstetric Trauma

Anal incontinence (AI) following childbirth generally results from either direct damage to the internal (IAS)/external anal sphincters (EAS), pudendal nerve injury, or a combination of the two. The reported rates of AI following primary repair of obstetric anal sphincter injuries (OASIS) range between 15% and 61%, with a mean of 39%. Three-dimensional endoanal ultrasound (3D-EAUS) has been recommended as the gold standard technique for the assessment of anal sphincter integrity, as the circumferential and longitudinal extension of muscular defects may be visualized using multiplanar reconstructions. Isolated anterior EAS tears and combined EAS and IAS tears are typical of obstetric sphincter damage, however, isolated IAS injury is extremely uncommon. Missed anal sphincter injuries are identified by EAUS in up to 29% of primiparous females after vaginal births. Unlike damage to the anal sphincters, levator ani and puborectalis muscle damage are best investigated by transperineal ultrasound, endovaginal ultrasound or magnetic resonance imaging because these modalities allow visualization of the attachment of the muscles to the inferior pubic rami. Imaging may influence the surgical treatment of OASIs and choice of mode of subsequent birth.