Reports name levels by the two vertebrae on either side of a disc. Knowing the map makes the report far less opaque.
What do spinal levels mean?
- The spine runs C1–C7 in the neck (cervical), T1–T12 in the mid-back (thoracic), L1–L5 in the low back (lumbar), then the fused sacrum (S1–S5).
- “L4-L5” means the disc between the fourth and fifth lumbar vertebrae. “L5-S1” is the disc between the last lumbar vertebra and the sacrum — the lowest and most heavily loaded level, and the most common site of herniation.
- Each nerve root supplies a predictable strip of skin and a predictable set of muscles, which is how the level is confirmed by examination.
How can an exam tell which spinal level is the problem?
This is why a good examination can often predict the scan. If your numbness is on the outer calf and the top of the foot and you cannot lift your toes, the L5 root is the suspect — and the scan is being used to confirm what the examination already suggested, not to go looking blindly.
Remember the general rule. Findings like this one are common in people with no pain at all, and become steadily more common with age. A finding on a report is not a diagnosis until someone has matched it to your symptoms and your examination. See understanding your MRI report.
Bring your scan and report in and we will go through it with you. Call us or request an appointment.
What do L4-L5 and L5-S1 mean on an MRI?
Spinal levels are named for the vertebrae between which a disc sits: L4-L5 is the disc between the fourth and fifth lumbar vertebrae, L5-S1 the one between the fifth lumbar vertebra and the sacrum. The lowest two lumbar levels carry the most load and are by a wide margin the most commonly affected. The naming matters because each level has a matching symptom map — L4-L5 problems typically affecting the L5 nerve root and referring to the outer calf and top of the foot, L5-S1 typically affecting S1 and referring to the back of the calf, outer sole and heel.
Frequently asked questions
Why are L4-L5 and L5-S1 mentioned so often?
They carry the greatest load and sit at the greatest angle, so they degenerate and herniate more than the levels above.
Does the level tell you where I will feel pain?
Broadly yes. Each root has a characteristic territory, and matching the reported level to your symptoms is a key part of interpreting the scan.
What does S1 mean?
The first sacral segment. L5-S1 is the disc between the lowest lumbar vertebra and the sacrum, and it is the most commonly herniated level in the spine.
How are the vertebrae in the spine numbered?
From the top down. The neck has seven cervical vertebrae, C1 to C7. The mid-back has twelve thoracic vertebrae, T1 to T12. The low back has five lumbar vertebrae, L1 to L5. Below them sits the sacrum, S1 to S5, which is fused. A disc is named by the two vertebrae on either side of it, so L4-L5 is the disc between the fourth and fifth lumbar vertebrae.
What symptoms come from an L4-L5 or L5-S1 problem?
Each level has its own map. An L4-L5 problem typically affects the L5 nerve root, which refers to the outer calf and the top of the foot and can make it hard to lift your toes. An L5-S1 problem typically affects the S1 root, which refers to the back of the calf, the outer sole and the heel. Matching that map to your scan is how the level is confirmed.
Sources
- Fardon DF et al. Lumbar disc nomenclature: version 2.0: Recommendations of the combined task forces of the North American Spine Society, the American Society of Spine Radiology and the American Society of Neuroradiology. The spine journal : official journal of the North American Spine Society, 2014. PubMed 24768732
- Williams AL et al. Lumbar disc nomenclature: version 2.0. AJNR. American journal of neuroradiology, 2014. PubMed 25339648
- Brinjikji W et al. Systematic literature review of imaging features of spinal degeneration in asymptomatic populations. AJNR. American journal of neuroradiology, 2015. PubMed 25430861
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