Spinal stenosis is a condition defined by the narrowing of spaces within the spine, which creates pressure on the nerves that travel through the backbone. This structural change can occur in the central spinal canal or in the openings where nerve roots exit, called the neuroforamen. It most commonly affects the lower back (lumbar stenosis) and the neck (cervical stenosis). While lumbar stenosis is more frequent, cervical stenosis is often considered more serious because it can compress the spinal cord itself.
Structural Changes Leading to Narrowing
The progression of spinal stenosis begins with age-related wear and tear, primarily involving degenerative changes in the spinal structures. Intervertebral discs, which act as shock absorbers, begin to degenerate and lose height. This loss of disc space causes an abnormal transfer of force to the facet joints, leading to arthritis and joint enlargement (hypertrophy).
The body responds to this instability by forming bony overgrowths, called osteophytes or bone spurs, which project into the spinal canal and foraminal openings. Ligaments, particularly the ligamentum flavum, can also thicken and buckle into the canal due to chronic stress. These cumulative changes—bulging discs, thickened ligaments, and enlarged bone structures—progressively reduce the space available for the spinal cord and nerve roots, causing the nerve compression that characterizes spinal stenosis.
Classifying Severity
The clinical progression of spinal stenosis is described using descriptors of severity: mild, moderate, or severe. In the mild stage, symptoms are often intermittent and minimal, sometimes only appearing after specific movements or prolonged standing. Daily function is minimally impacted, and discomfort is usually managed with simple measures.
Moderate stenosis is marked by more consistent and noticeable symptoms, most frequently including neurogenic claudication. This condition is characterized by pain, cramping, or weakness in the legs brought on by walking or standing, and relieved by sitting or leaning forward. Patients at this stage typically experience a noticeable reduction in their comfortable walking distance.
The severe stage indicates significant functional impairment and a substantial impact on quality of life. Pain may be constant and unrelenting, even at rest, and is often accompanied by motor weakness or sensory loss in the limbs. The most serious presentations involve the potential for bowel or bladder dysfunction, which signals a critical level of nerve compression requiring immediate attention.
The Role of Diagnostic Imaging in Assessment
Medical professionals use diagnostic imaging to objectively measure the degree of narrowing and confirm the classification. Magnetic Resonance Imaging (MRI) is the preferred tool for visualizing soft tissues like discs, ligaments, and the spinal cord, providing detailed images of compressed neural structures. Computed Tomography (CT) scans are also utilized, offering superior detail on the bony anatomy, which is helpful for presurgical planning.
Radiological criteria grade the stenosis by measuring the space available for the nerves. For central canal stenosis, a common measurement is the anteroposterior (AP) diameter of the spinal canal; an AP diameter less than 10 millimeters in the lumbar spine is often indicative of stenosis. Qualitative assessment of the cerebral spinal fluid (CSF) around the nerves, using grading systems like the Lee or Schizas classifications, is another method.
For foraminal stenosis, which involves the side openings where nerves exit, key measurements include the foraminal diameter and the height of the lateral recess. A foraminal diameter of less than 3 millimeters on sagittal images is often a diagnostic threshold. Imaging findings must always be correlated with the patient’s reported symptoms to accurately determine the overall stage and guide treatment decisions.