Anatomy relevant to lumbar puncture

Vivian Imbriotis | May 25, 2026

In lumbar puncture, a needle in inserted posteriorly in the midline into the intrathecal space to remove or sample CSF.

Surface anatomy

  • 5 thoracic vertebrae
  • T1/2: termination of spinal cord \(\to\) becomes cauda equina
  • T4: in line with line joining L + R ASIS
  • T4/5: site of needle insertion

Needle passes through:

  1. Skin
  2. Subcutis \(\to\) fat
  3. Supraspinous ligament \(\to\) interspinous ligament \(\to\) ligamentum flavum
  4. epidural fat
  5. dura and arachnoid mater
  6. epidural space with CSF and cauda equina

Sagittal

Transverse