Spinal Stenosis (Mild, Moderate, Severe) on Radiology Reports: What It Means

“Spinal stenosis” means narrowing of the spinal canal or bony tunnel that surrounds the spinal cord.   On MRI, radiologists describe the degree of narrowing as mild, moderate, or severe based on how much narrowing there is.  The severity is about anatomy on the images and not pain levels. Below is a plain-English article on what the MRI shows and what those words usually mean.

What “stenosis” means on MRI

Stenosis is simply narrowing. On MRI, we look at three main areas:

• Central canal (the tunnel for the spinal cord/cauda equina)

• Lateral recess (the side gutters where nerve roots travel before exiting)

• Neural foramina (the exit holes for each nerve root)

Your report may mention stenosis in one, two, or all three. It may also list the spine region (cervical neck, thoracic mid-back, or lumbar lower back) and specific levels (like L4–L5).

Why MRI is the preferred test

MRI shows soft tissues (discs, nerves, ligaments) , fluid (cerebrospinal fluid or CSF) and bones without radiation. Because we can see the CSF and normal fat around nerves, MRI is excellent at judging whether nerves are free, crowded, or compressed—which maps to the mild/moderate/severe language on your report.

Common causes of spinal stenosis seen on MRI

• Disc bulge or herniation (the disc protrudes backward)

• Facet joint arthritis (overgrowth of the small back joints)

• Ligamentum flavum thickening (ligament in the canal becomes bulky)

• Spondylolisthesis (one vertebra slips over another)

• Scoliosis (curvature narrowing one side more than the other)

• Bony spurs or congenital (naturally tight) canal

• Cervical OPLL (ossification of the posterior longitudinal ligament, less common but important in the neck)

The report often lists a mix of these, because stenosis usually results from several changes stacking up at the same level.

How radiologists grade stenosis on MRI

There are published grading systems, but the idea is consistent: what matters is the space left for the nerves and cord.

Central canal stenosis (spinal cord/cauda equina tunnel)

• Mild: The canal is a bit narrowed, but CSF still surrounds the cord or the nerve roots of the cauda equina.

• Moderate: Narrowing has partly squeezed out the CSF. The nerves look crowded, but not completely compressed. There may be partial touching or bunching of nerve roots.

• Severe: CSF is gone at that level and the nerves are markedly compressed/crowded. In the neck, the spinal cord may be indented or flattened; in the low back, cauda equina roots clump together with essentially no surrounding fluid.

Practical read: when you see phrases like “effacement of CSF,” “nerve root crowding,” or “cord indentation,” the report is moving from mild toward moderate or severe.

Lateral recess stenosis (side gutters before the exit)

• Mild: The recess is mildly narrowed.

• Moderate: Contact between disc/facet/ligament and the traversing nerve root with limited surrounding CSF; the nerve looks crowded.

• Severe: The traversing nerve root is clearly compressed or displaced, often with no residual CSF around it.

Foraminal stenosis (nerve exit holes)

Radiologists look for the normal fat that surrounds each exiting nerve root in the foramen:

• Mild: Some fat remains around the nerve root; the opening is narrowed but not tight.

• Moderate: Fat is mostly effaced (squeezed out) and the nerve root is in contact with disc or bone.

• Severe: No visible fat and the nerve root appears indented or flattened by disc/osteophyte; the foramen looks markedly narrowed or “collapsed.”

Cervical vs lumbar stenosis: what MRI looks for

• Cervical (neck): We focus on spinal cord shape and signal. Severe stenosis may indent the cord; if the cord shows high T2 signal, that can suggest chronic pressure (myelopathy risk).

• Lumbar (low back): We assess cauda equina roots and the ability for fluid/roots to move. Severe central stenosis can relate to neurogenic claudication (leg heaviness/pain with walking). Foraminal stenosis often tracks with radicular symptoms in a specific nerve (e.g., L5).

Do “mild, moderate, severe” match symptoms?

Not always. MRI shows structure, while symptoms reflect how your nerves react. Some people with “severe” narrowing have mild symptoms; others with “moderate” narrowing feel significant pain or weakness. That’s why your doctor matches the MRI with your symptoms and history.

Typical phrases you might see in your report (decoded)

• “Mild central canal stenosis at L4–L5 due to disc bulge and ligamentum flavum thickening.”
  → Tunnel is a bit narrow; fluid still likely present; nerves not tightly pinched.

• “Moderate lateral recess stenosis contacting the traversing L5 nerve roots.”
  → Side gutters are narrowed; nerves are crowded/touched, which can explain leg symptoms.

• “Severe right foraminal stenosis with nerve root compression.”
  → Exit hole is very tight on the right; the exiting nerve is compressed—often correlates with side-specific radiating pain or numbness.

• “Cord indentation without cord signal change.”
  → The cord is pushed but not showing abnormality; still clinically relevant, especially in the neck.

• “CSF effacement at L3–L4.”
  → The normal fluid cushion is gone there—suggesting at least moderate, often severe, central narrowing.

What changes the grade over time?

Stenosis can worsen slowly due to aging joints and ligaments, or improve if a large soft disc herniation shrinks over months. Weight management, posture/ergonomics, and core/hip strength can reduce mechanical load, but the imaging grade itself mainly changes when the structure changes (disc resorption, surgical decompression, or progression of arthritis/ligament thickening).

How MRI severity guides next steps (imaging-focused view)

• Mild stenosis
  Often managed conservatively. MRI is useful to rule out worrisome causes and to document the baseline. Follow-up imaging is usually not needed unless symptoms change significantly.

• Moderate stenosis
  Helps target injections (e.g., foraminal vs central) and therapy toward the levels and sides that are actually narrowed on MRI. If symptoms persist despite treatment, the MRI can guide surgical planning.

• Severe stenosis
  MRI pinpoints exact levels for potential decompression and shows if multiple compartments (central, lateral recess, foramina) are involved.

When additional imaging may be suggested

• Flexion/extension X-rays for instability or spondylolisthesis.

• CT when bone anatomy needs precise definition (e.g., pre-op planning, ossification).

• Contrast MRI in specific situations (post-op scarring vs disc, tumor, infection).

Key takeaways you can skim

• Mild = narrowing but space remains (CSF/fat still visible).

• Moderate = crowding with partial loss of CSF/fat and contact with nerves.

• Severe = no space left (CSF/fat gone) and definite nerve compression.

• Severity on MRI does not equal symptom severity; clinical correlation matters.

• Your report’s phrases (CSF effacement, nerve root contact/compression) map directly to these grades.

Conclusion

“Mild, moderate, and severe” spinal stenosis on MRI describe how much room nerves still have in the canal, lateral recess, and foramina. Radiologists grade stenosis by looking for preserved fluid or fat versus crowding or compression of nerves. This imaging language helps your care team match symptoms to specific levels, choose treatments, and plan targeted procedures if needed. Remember that MRI findings need to always be correlated to your symptoms by your doctors.

References

https://radiopaedia.org/articles/spinal-stenosis-1?lang=us

https://www.ncbi.nlm.nih.gov/books/NBK531493/

https://my.clevelandclinic.org/health/diseases/17499-spinal-stenosis