Axial T2 MRI of the lumbar spine

1. A Right L4 exiting nerve root.

2. B Right L5 nerve root.

3. C Right superior articular facet of L5.

4. D Right inferior articular facet of L4.

5. E Ligamentum flavum.

The nerves of the cauda equina are well demonstrated on T2-weighted axial imaging of the lumbar spine. They appear as low signal intensity punctate structures within the bright signal intensity of the surrounding cerebrospinal fluid. The cauda equina are the continuing nerve roots from the cord, which gradually decrease in number as the root pairs exit the spinal column. Within the thoracolumbar spine the nerve roots exit at the exit foramen below the root. For example, the L4 nerve root exits at L4/L5, and is the traversing nerve root at L3/L4.

The ligamentum flavum is a collection of ligaments attached to the vertebral laminae running all the way from C2 to S1. They are seen posteriorly on the interior of the vertebral canal. Hypertrophy of these ligaments can lead to canal stenosis. The facet joints are well demonstrated on this image, with the inferior facets of the vertebra above (L4) lying posterior to the superior facets of the vertebra below (L5).