US identification of the anal sphincter complex and levator ani muscle in neonates: Infracoccygeal approach

PURPOSE: To identify the anal sphincter complex and levator ani muscle at t ransperineal ultrasonography (US) with the infracoccygeal approach. MATERIALS END METHODS: Infracoccygeal US was performed with a 7-MHz linear- array transducer in 40 healthy neonates. The babies were placed in the supi ne position, and both legs were drawn up to the chest. The buttocks were ac cordingly lifted up. The approach site was just inferior to the coccyx and posterior to the anus. Scanning was performed to obtain transverse images o f the anorectal area. The thickness of the anal sphincter complex and the p uborectalis muscle were measured. RESULTS: Infracoccygeal US revealed the internal anal sphincter (IAS), the external anal sphincter (EAS), and the puborectalis muscle in all babies. T he IAS and EAS were depicted as inner and outer hypoechoic ringlike structu res, respectively. A round, hyperechoic space (intersphincteral space) was present between the hypoechoic IAS and EAS. The puborectalis muscle was ide ntified as a U-shaped hypoechoic structure. The bulbocavernosus and ischioc avernous muscles were also identified. Mean thicknesses were as follows: IA S, 1.3 mm +/- 0.3 (SD) (range, 0.8-1.9 mm); EAS, 1.6 mm +/- 0.3 (range, 1.2 -2.3 mm); and puborectalis muscle, 1.1 mm +/- 0.3 (range, 0.6-1.9 mm). CONCLUSION: Infracoccygeal transperineal US is an excellent diagnostic moda lity for demonstrating the anal sphincter complex and levator ani muscle in neonates.