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.
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Epidemiology
The most commonly affected area is the lumbar spine (see: lumbar canal stenosis), followed by the cervical spine 6.
Men are more affected than women (except in the case of degenerative spondylolisthesis). Prevalence increases with age; most newly diagnosed patients are >50 years old 2.
Pathology
Etiology
The causes of spinal stenosis can be divided into two groups 1:
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bony structures
facet osteophytes
posterior vertebral body osteophytes (uncinate spurs)
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soft tissue structures
hypertrophy or bulking of the ligamentum flavum
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
Classification
There are two main classification categories:
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etiologic classification
congenital: e.g. congenital lumbar spinal stenosis (some associated with achondroplasia)
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acquired
arthritic changes
iatrogenic
traumatic
inflammatory
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anatomic classification
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central: can be subdivided due to different clinical presentation and treatment 6
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lateral: most commonly due to osteophyte formation
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foraminal: between the medial and lateral border of the pedicle
extraforaminal: lateral to the lateral edge of the pedicle
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Radiographic features
Plain radiograph
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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
Fluroscopy
Plain radiographic myelography provides dynamic information such as the degree of cutoff when a patient performs extension.
CT
Spinal stenosis has been defined as a cross-sectional area <100 mm2 or <10 mm AP diameter on axial CT 4,5.
CT myelography findings may include:
central and lateral neural element compression
bony anomalies
bony facet hypertrophy
MRI
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.