Lumbar Spinal Stenosis¶

Definition¶

Lumbar spinal stenosis (LSS) is the narrowing of the lumbar spinal canal, lateral recesses, or neural foramina resulting in compression of the cauda equina or individual nerve roots. It is the most common reason for spinal surgery in patients over 65 years of age.

Etiology¶

LSS is almost always degenerative and multifactorial:

Disc bulging/herniation (anterior)
Ligamentum flavum hypertrophy (posterior) — often the dominant contributor
Facet arthropathy with hypertrophy (posterolateral)
Degenerative spondylolisthesis (dynamic, positional)
Congenitally narrow canal (predisposition to earlier symptoms)

Most common levels: L4–L5 (most common), followed by L3–L4 and L5–S1.

Clinical Presentation¶

Neurogenic claudication: bilateral leg pain, heaviness, numbness, and weakness provoked by walking and standing; relieved by sitting or forward flexion
Distinguished from vascular claudication (relieved by standing still; absent pulses)
Radiculopathy: unilateral leg pain in a dermatomal distribution from lateral recess or foraminal stenosis
Cauda equina syndrome (rare): bilateral leg weakness, saddle anesthesia, bladder/bowel dysfunction — surgical emergency

Imaging Findings¶

MRI — Gold Standard¶

Sagittal T2: multilevel CSF effacement; "hourglass" narrowing at affected levels
Axial T2: trefoil or cloverleaf canal shape; loss of CSF around cauda equina roots; nerve root crowding
Sagittal T1: foraminal fat obliteration for foraminal stenosis assessment
Dural sac cross-sectional area <100 mm² = severe; <75 mm² = extreme
Redundant nerve roots (tortuous, coiled appearance of cauda equina) indicates chronic severe stenosis

CT/CT Myelography¶

Useful when MRI is contraindicated
CT myelography shows contrast column narrowing at stenotic levels
Superior for evaluating bony contributions to stenosis

Clinical Pearl

Upright or axial-loaded MRI can reveal stenosis not visible on conventional supine MRI. In the supine position, disc bulging and ligamentum flavum buckling may be reduced, underestimating the degree of stenosis. Some centers offer upright MRI or use axial-loading devices to simulate weight-bearing conditions. This is particularly useful when clinical symptoms are severe but supine MRI shows only mild stenosis.

Key Points¶

LSS is the most common indication for spine surgery in the elderly
Usually multifactorial — disc + ligamentum flavum + facets
L4–L5 is the most commonly affected level
Neurogenic claudication is the classic presentation — positional leg symptoms
MRI is the gold standard — axial T2 for grading, sagittal T1 for foraminal assessment
Cauda equina syndrome is a rare but critical complication requiring emergency surgery

References¶

Kreiner DS, Shaffer WO, Baisden JL, et al; North American Spine Society. An evidence-based clinical guideline for the diagnosis and treatment of degenerative lumbar spinal stenosis (update). Spine J. 2013;13(7):734-743. PMID: 23830297. https://pubmed.ncbi.nlm.nih.gov/23830297/
Schizas C, Theumann N, Burn A, et al. Qualitative grading of severity of lumbar spinal stenosis based on the morphology of the dural sac on magnetic resonance images. Spine (Phila Pa 1976). 2010;35(21):1919-1924. PMID: 20671589. https://pubmed.ncbi.nlm.nih.gov/20671589/
Deer T, Sayed D, Michels J, Josephson Y, Li S, Calodney AK. A review of lumbar spinal stenosis with intermittent neurogenic claudication: disease and diagnosis. Pain Med. 2019;20(Suppl 2):S32-S44. PMCID: PMC7101166. https://pmc.ncbi.nlm.nih.gov/articles/PMC7101166/
Munakomi S, Foris LA, Varacallo MA. Spinal Stenosis and Neurogenic Claudication. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; updated August 13, 2023. https://www.ncbi.nlm.nih.gov/books/NBK430872/
Seo J, Lee JW. Magnetic resonance imaging grading systems for central canal and neural foraminal stenoses of the lumbar and cervical spines with a focus on the Lee grading system. Korean J Radiol. 2023;24(3):224-234. https://www.kjronline.org/DOIx.php?id=10.3348%2Fkjr.2022.0351
Steurer J, Roner S, Gnannt R, Hodler J. Quantitative radiologic criteria for the diagnosis of lumbar spinal stenosis: a systematic literature review. BMC Musculoskelet Disord. 2011;12:175. PMCID: PMC3161920. https://pmc.ncbi.nlm.nih.gov/articles/PMC3161920/
Lumbar canal stenosis. Radiopaedia.org. https://radiopaedia.org/articles/lumbar-canal-stenosis-1