What is Spinal Stenosis?
Spinal stenosis is a narrowing of the spinal canal that results in bony constriction of the cauda equina and emerging nerve roots, which can compress neural and vascular structures. 1
Anatomical Definition
The condition involves reduced space available for neural and vascular elements within the spinal column, occurring when the normal sagittal diameter of the lumbar canal (normally 15-25 mm) decreases below 12 mm, confirming stenosis. 2, 3
Stenosis can affect multiple anatomical locations: the central spinal canal, lateral recess (nerve root canal), or intervertebral foramina, and may be localized to one segment or involve multiple levels. 2, 3
The narrowing can result from bone structures, soft tissues, or both, affecting either the bony canal itself or the dural sac containing the spinal cord and nerve roots. 3
Types of Spinal Stenosis
Cervical Stenosis
- Occurs in the neck region and can compress the spinal cord, leading to myelopathy with symptoms including gait disturbances, balance problems, fine motor skill deterioration in the hands, and bowel or bladder dysfunction in advanced cases. 4, 5, 6
Lumbar Stenosis
- Affects the lower back and is the most common form, particularly in patients over 65 years, representing the most frequent reason for spinal surgery in this age group. 7, 8
Clinical Presentation
Neurogenic Claudication
- The hallmark symptom is neurogenic claudication: leg pain (and occasionally weakness) that occurs with walking or standing and is relieved by sitting or spinal flexion. 1
Additional Symptoms
Low back pain with radiating symptoms into the buttocks, thighs, or lower legs, often accompanied by weakness, numbness, or tingling. 1, 4, 2
Radiculopathy presents as dysfunction of a nerve root with pain, sensory impairment, weakness, or diminished deep tendon reflexes in a specific nerve root distribution. 1
Symptoms typically worsen with standing, walking, or lumbar extension and improve with forward flexion, sitting, or lying down. 7
In severe cases, bowel or bladder dysfunction may develop, indicating cauda equina syndrome—a surgical emergency. 1, 4, 5
Causes and Risk Factors
Congenital-Developmental Stenosis
- Some individuals are born with a congenitally narrow spinal canal, with thickened laminae and shortened pedicles that remain asymptomatic until later degenerative changes precipitate symptoms. 3
Acquired Stenosis
Degenerative changes are the most common cause in adults, including disc herniation, osteophyte (bone spur) formation, ligament thickening, and facet joint hypertrophy. 1, 2
In achondroplasia patients, stenosis occurs predominantly in the thoracolumbar region due to mushroom-shaped vertebral bodies, shortened pedicles, and short interpedicular distances. 1
Iatrogenic stenosis can occur after previous spinal surgery, such as disc removal or laminectomy. 3
Natural History
The disease course is variable and often unpredictable, with many patients experiencing slow, stepwise decline interspersed with long periods of stability or even improvement. 4, 5
Rapid deterioration is rare, and symptoms often wax and wane over time, which is why surgery is almost always elective rather than emergent (except for cauda equina syndrome). 7
Untreated severe stenosis carries significant risks: cervicomedullary compression has a 16% mortality rate if left untreated, and prolonged severe stenosis can lead to demyelination of white matter with potentially irreversible neurological deficits. 5, 6
Diagnostic Considerations
The diagnosis requires correlation of clinical symptoms, physical examination findings, and radiological changes—imaging abnormalities alone do not establish the diagnosis. 2
Asymptomatic radiographic stenosis is common in older adults and does not require intervention, as degenerative changes on imaging correlate poorly with symptoms. 1
MRI is the gold standard for evaluating both the osseous spinal column and spinal cord, with T2-weighted signal changes indicating myelopathy. 4, 5