Sonography of occult dysraphism in neonates and infants with MR imaging correlation.

High-resolution spinal sonography has become an accepted study to screen for occult dysraphic lesions (ODLs) in neonates and infants. These defects are thought to be caused by abnormal fusion or closure of embryonic dorsal midline structures. Sonographic findings suggestive of an ODL include low position of the conus, nontapered bulbous appearance of the conus, dorsal location of the cord within the bony canal, solid or cystic masses in the distal canal or soft tissue of the back extending toward the canal, patulous distal thecal sac, and thick filum. Physical findings suggestive of ODLs include lumbosacral skin dimples, lumbosacral masses, lower extremity weakness, and an extra appendage arising from the back. The appearances of a normal infant spine, dorsal dermal sinus, lipoma, lipomyelomeningocele, lipomyelocele, myelocystocele, and diastematomyelia are depicted sonographically and correlate with those on magnetic resonance (MR) images. MR imaging is most useful when sonographic findings are abnormal or equivocal or when normal skeletal maturation limits sonographic visualization of the intracanalicular contents.