A lumbar puncture is planned in an infant. Compared with an adult, the conus medullaris in a full-term newborn typically terminates at which vertebral level?

• A Lower border of L1
• B Upper border of L2
• C Upper border of S1
• D Lower border of L3 ✓

Explanation

At birth the vertebral column grows faster than the spinal cord, so the conus medullaris ends at about the lower border of L3 in the newborn and rises to its adult position at approximately the lower border of L1 by early childhood. This difference matters because the dural sac still extends to S2, allowing safe lumbar puncture below L3 in neonates rather than below L1.

Reference: Moore's Clinically Oriented Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.