Normal fetal sacrum simulating spina bifida: "pseudodysraphism".

An erroneous diagnosis of spina bifida may be made using obstetric ultrasound (US) if the examiner is unfamiliar with normal fetal sacral anatomy or the ways in which artifacts can affect the appearance of the normal lumbosacral posterior elements. Two normal neonates who appeared to have sacral dysraphism in utero are described and compared with US and CT studies of an anatomically normal 34-week cadaver specimen. In the event of transducer angulation, lumbosacral spina bifida must be diagnosed with the utmost caution if an associated sac or mass is not present.