Ultrasound determination of the normal location of the conus medullaris in neonates.

PURPOSE To establish the normal range of the position of the conus medullaris in neonates and determine whether it differs from that in adults. METHODS One hundred five healthy neonates born over an 18-day period in a single obstetric unit had ultrasound examinations of their lower spines to relate the conus medullaris to the nearest intervertebral disk or midvertebral level. RESULTS The mean position of the conus was midway between the L1-2 disk and mid-L-2 body, ranging from T-12/L-1 to L-3, with the modal position being L1-2 (47.6%). A small but significant rise in position from 33 to 42 weeks postconceptual age was identified. Comparison with data previously reported from adults showed a small but highly significant difference in conus position of approximately 0.25 vertebral levels. DISCUSSION Our data confirm studies suggesting that ascent of the cord after birth is minor.