The conus medullaris: normal US findings throughout childhood.

A prospective ultrasound (US) study of children without neurologic or spinal problems or midline cutaneous abnormalities on the back was performed to determine the level of the conus medullaris in healthy children. The tip of the conus was identified in sagittal and transverse planes, and a radiopaque bead was placed on the skin to mark the location of the tip. Findings at subsequent radiography confirmed the vertebral level. A total of 161 children, aged 4 days to 13 years 5 months (mean, 3 years 7 months; median, 3 years 1 month), composed the study population. Conus levels in these healthy children varied from the level of T10-11 interspace to the superior aspect of the L-3 vertebra. However, in only two children were the conus levels below the middle portion of L-2. Estimations of vertebral levels of the conus based on the US scan alone were within one vertebral level of the level determined at radiography in 145 of 161 (90%) cases. Palpable landmarks, the tip of the lowest rib and the iliac crest, corresponded to the level of the L-2 and L-5 vertebrae, respectively. The conus medullaris can be located at US in most children, even beyond infancy. The normal levels are constant throughout childhood.