A scan report mentioning nerve compression is alarming to read. In many cases it means very little. Here is how to tell when it matters.
Being told your scan shows nerve compression is a common cause of worry, and one I hear about frequently in clinic. Let me explain what it actually means, when it is serious, and when it can reasonably be left alone.
How nerves leave the spine
Your spine is a stack of bones called vertebrae. Running up the middle is a tunnel that continues all the way to the brain, containing and protecting the spinal cord and a great many nerves. At each level, between two bones, a nerve exits the spine through a window at the side.
In the lumbar spine, the lower back, those nerves mostly travel down the legs, supplying the muscles and the skin.
A nerve there can be compressed, most commonly by a herniated disc, but also by thickened ligaments or facet joints overgrown through wear and tear. When compressed, it can send pain down that leg, and cause numbness and tingling. Where compression is severe or long-standing, weakness in the leg can develop.
The same applies in the cervical spine, the neck, where nerves supply the muscles of the arm and hand and provide sensation to the skin. Compression there causes pain shooting down the arm, known as cervical radiculopathy, often with numbness and tingling in the hand or arm, and weakness if the compression is severe.
An important distinction: the spinal cord
This should not be confused with compression of the spinal cord itself.
On an MRI, the spinal cord appears as a grey structure running from the top of the neck downwards. It transmits messages between the brain and the rest of the body.
Think of the spinal cord as a tree trunk, with the individual nerves as branches coming off it. The trunk is the critical structure, because disruption there affects the flow of messages to multiple parts of the body at once.
Compression of the spinal cord in the neck can cause weakness in both arms and legs, or, lower down, weakness in both legs. These symptoms are referred to as cervical myelopathy, which deserves its own discussion.
When the scan says one thing and your body says another
Here is the situation I want to address directly.
Perhaps you have had back pain without much travelling down the legs, but your MRI report mentions potential nerve compression or irritation. That is a common finding in itself.
As a surgeon, I am really only interested in it if it is causing leg symptoms. We frequently see compression in people with no leg symptoms whatsoever, because nerves tolerate a certain amount of compression and continue to function perfectly well.
Why the early weeks are so painful
There is a useful explanation for something many patients experience.
At the onset of a disc herniation, as the disc begins to bulge, it can release inflammatory chemicals. These are effectively a liquid, and you do not see them on an MRI, but they stir up a substantial inflammatory process.
Around that time everything hurts. The pain feels intense and severe, and you may get pain down the leg, largely from inflammation around the nerve rather than the compression itself.
Often it settles, and the pain disappears even though the compression remains. That does not mean surgery is required. If the function of your leg is fine and the pain has improved, listen to your body. No operation is needed.
So when does it matter?
Nerve compression matters when you have symptoms belonging to that nerve:
- In the lumbar spine: pain radiating down the leg, with weakness or numbness
- In the cervical spine: pain radiating down the arm, with weakness or numbness
The key takeaway
In medicine we are taught to treat the patient, not the scan. That is why a good clinical assessment is paramount, and why the skill lies in tying the findings to the clinical picture rather than reading the report in isolation.
