Lumbar Spinal Canal Stenosis Diameter Thresholds
Lumbar spinal stenosis is generally defined as an anteroposterior (AP) diameter of the spinal canal less than 12 mm, with absolute stenosis confirmed at diameters less than 10 mm. 1, 2
Diagnostic Diameter Criteria
Central Canal Stenosis
- AP diameter < 12 mm is considered diagnostic for lumbar spinal stenosis 1, 3
- AP diameter < 10 mm confirms absolute stenosis 4, 2
- Normal lumbar canal AP diameter ranges from 15-25 mm (or 18-20 mm in some references), with measurements below this range considered suggestively abnormal 1, 5
- Cross-sectional area < 70 mm² is an alternative quantitative measure for central stenosis 2
Lateral Recess Stenosis
- Height < 3 mm is suggestive of lateral recess stenosis 1
- Height < 2 mm is diagnostic for lateral recess stenosis 1
Clinical Context and Measurement Considerations
The diameter thresholds represent morphological criteria that must be interpreted alongside clinical presentation. Stenosis can be classified as:
- Local/segmental stenosis: affecting single levels 1
- Generalized stenosis: involving multiple levels (2-4 levels) 1
- Central vs. lateral: compression of the thecal sac centrally versus individual nerve roots laterally 5
Important Caveats
Congenital-developmental stenosis may remain asymptomatic until later degenerative changes precipitate symptoms, even with canal diameters in the stenotic range 1. The presence of radiological stenosis does not automatically mandate surgical intervention—correlation with clinical symptoms (neurogenic claudication, radiculopathy, motor weakness) is essential 1, 3.
Moderate stenosis (AP diameter 11-14 mm) can still produce significant symptoms and may require surgical decompression, with excellent outcomes reported in this group 4. The 12 mm threshold should not be viewed as an absolute cutoff but rather as a diagnostic guideline that requires clinical correlation 1, 2.
Measurement Pitfalls
Multiple imaging parameters exist to quantify stenosis, but there is lack of consensus on standardized radiological criteria across clinical studies 2. CT and MRI provide the most accurate measurements, with myelography as an alternative when MRI is contraindicated 1, 2. Plain radiography is inadequate for assessing canal diameter and should not be relied upon 1.