Spinal Cord Extent: Understanding the End Point & Cauda Equina

The adult spinal cord (conus medullaris) typically terminates at the L1–L2 vertebral level (range T12–L3). It does not extend to the sacral vertebrae.

Anatomical Relationships

• Neonates: Cord ends at L3–L4.
• Adults: Differential growth—vertebral column elongates more than cord → cord ascends relatively.
• Conus medullaris: Tapered distal end of cord.
• Filum terminale: Pia mater extension from conus to coccyx (stabilizes cord).
• Cauda equina: Bundle of lumbar, sacral, and coccygeal nerve roots (L2–Co) descending in subarachnoid space, resembling a horse's tail.

Clinical Significance

• Lumbar puncture: Performed at L3–L4 or L4–L5 (below conus) to avoid cord injury.
• Spinal anesthesia: Injected into subarachnoid space at L3–L4.
• Cauda equina syndrome: Compression of nerve roots → saddle anesthesia, bowel/bladder dysfunction, leg weakness → surgical emergency.
• Conus medullaris syndrome: Cord tip injury → similar but more sudden, symmetric deficits.
• Imaging: MRI terminates scanning at L2 typically; cauda equina roots visible below.

Nerve Root Exit

Roots exit at their respective vertebral foramina. For example, L4 root exits at L4–L5 foramen, but its rootlet originates at L1 cord level and descends as part of cauda equina.

This arrangement explains why low-back pathology affects specific dermatomes/myotomes despite cord ending higher.