Lumbar spinal stenosis occurs when changes in and around the lower spinal canal reduce the space available for the nerves. Several structures can contribute to that narrowing and the anatomy involved varies from one person to another. Understanding what has reduced the available space and where the narrowing occurs provides important context for assessing the condition.
- Structures that can reduce space in the spinal canal.
- Central, lateral recess and foraminal narrowing.
- The relationship between MRI findings and symptoms.
- How the clinical significance of narrowing is assessed.
The nerves travelling into your legs pass through a confined space in the lower spinal canal. A disc bulge, enlarged facet joint or thickened ligament takes up some of that space and, in some cases, places pressure on nearby nerves. Several of these changes may occur at the same spinal level.
When you see Dr Simon Clark with symptoms that may be associated with spinal canal narrowing, your MRI provides anatomical detail that can be considered alongside your symptoms and examination findings.
What Causes the Lower Spinal Canal to Narrow?
Age-related degeneration affects the structures surrounding the canal in different ways. A disc may lose height or bulge towards the canal. The facet joints at the back of the spine may enlarge and develop bone spurs, while the ligamentum flavum may thicken or fold into the available space.
The causes of lumbar spinal stenosis therefore include changes such as:
- Disc bulging or loss of disc height
- Enlarged facet joints and bone spurs
- Thickening or inward folding of the ligamentum flavum
- Vertebral slippage, scoliosis and other structural changes
Several of these findings may be present on the same MRI. Each occupies space differently, so identifying the structures involved gives the diagnosis anatomical context.
Where Can Spinal Canal Narrowing Occur?
The lumbar canal is not a single uniform space. Central canal stenosis reduces the area available to the bundle of nerves within the main canal. Narrowing in the lateral recess affects the path of a nerve root before it leaves the spine, while foraminal stenosis affects the opening through which the nerve root exits.
For that reason, two people with lumbar spinal stenosis on MRI may have narrowing in different locations, affecting different nerves. The location on the scan needs to correspond with the distribution of the person’s symptoms.
What Your MRI Can Tell You About Lumbar Stenosis
MRI shows where narrowing is present and which structures are taking up space around the nerves. The amount of narrowing seen on the scan does not reliably indicate how severe a person’s symptoms will be.
The World Federation of Neurosurgical Societies Spine Committee notes that the severity of stenosis seen on imaging does not necessarily correlate with the severity of clinical symptoms.
You can also read more about lumbar spinal stenosis symptoms, causes and treatment options.
This is why lumbar stenosis symptoms remain important when interpreting the scan. Leg pain, heaviness, numbness, weakness and reduced walking distance provide clinical information about the nerves involved. Examination findings add further evidence when determining whether the narrowing seen on MRI accounts for those symptoms.
When Does Lower Spinal Canal Narrowing Become Clinically Significant?
A diagnosis of stenosis on an MRI report does not establish the treatment required. The cause and location of the narrowing need to correspond with the symptoms, neurological findings and effect on everyday function.
If you require assessment of the lower spinal canal in Adelaide, a lower back specialist can consider your imaging findings alongside your symptoms, neurological examination and everyday function when determining whether treatment may be appropriate.
If you are experiencing symptoms that may be related to narrowing of the lower spinal canal, an assessment can help determine whether the findings on your MRI correspond with your symptoms. Book an appointment with Dr Simon Clark in Adelaide to discuss your symptoms, imaging and appropriate next steps.
FAQs
What causes narrowing of the spinal canal in the lower back?
Narrowing of the spinal canal in the lower back occurs when structures around the nerves occupy some of the available space. Disc bulging, enlarged facet joints, bone spurs, thickened ligaments, vertebral slippage and spinal deformity are recognised causes.
Does lumbar spinal stenosis always cause symptoms?
Lumbar spinal stenosis without symptoms is possible. The amount of narrowing seen on MRI does not reliably predict symptom severity, so the location of the stenosis and the clinical findings need to be considered together.
What does an MRI show in lumbar spinal stenosis?
MRI findings in lumbar spinal stenosis show the location of narrowing and the structures contributing to it. The scan can also show which neural structures may be affected by compression, while examination and symptom patterns help establish the clinical relevance of those findings.