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Spinal stenosis is a condition in which a portion of the spinal canal narrows to the point at which it can exert pressure on the nerves that travel through the spine.
Spinal stenosis is not to be confused with foraminal stenosis which is the narrowing of the foramina with subsequent compression of the nerve roots.
Men are more affected than women (except in the case of degenerative spondylolisthesis). Prevalence increases with age - most newly diagnosed patients are over the age of 50 years 2.
The causes of spinal stenosis can be divided into two groups 1:
- bony structures
- soft tissue structures
Acquired causes are more common than congenital ones, with the most common cause being osteoarthritis. Other causes include 3:
- injuries: may fracture or inflame a part of the spine
- tumors: spinal lesions, both benign and malignant, may cause spinal stenosis by compressing the cord
- Paget disease of bone: a condition where bones grow abnormally large and brittle; when it involves a vertebra, there is resultant narrowing of the spinal canal and nerve compression
There are two main classification categories:
- etiologic classification:
- anatomic classification
- central - cross-sectional area <100 mm2 or <10 mm AP diameter on axial CT 4,5
- lateral - most commonly due to osteophyte formation -
- foraminal - between the medial and lateral border of the pedicle
- extraforaminal - lateral to the lateral edge of the pedicle
- standing AP and lateral may show nonspecific degenerative findings (disc space narrowing, osteophyte formation)
- less frequent are degenerative scoliosis and degenerative spondylolisthesis
- flexion/extension radiographs may show segmental instability and subtle degenerative spondylolisthesis
Plain radiographic myelography provides dynamic information such as the degree of cutoff when a patient performs extension.
Findings may include:
- central and lateral neural element compression
- bony anomalies
- bony facet hypertrophy
Findings may include:
- central stenosis, with the thecal sac measuring <100 mm2 in area 5
- obliteration of perineural fat and compression of lateral recess or foramen
- facet and ligament hypertrophy
- spinal stenosis may be incidentally discovered in asymptomatic patients
Lumbar spinal stenosis grading is based on the distribution of the cauda equina nerve roots and CSF within the thecal sac.
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