Spinal stenosis: pathophysiology, clinical and radiologic classification

Stenosis is the narrowing of a hollow tube, in this case the central lumbar spinal canal, lateral recess, or foramen. Clinically, this narrowing produces neurovascular compression that may lead to pain. Lumbar spinal stenosis may be classified by etiology (for example, congenital or acquired) or by symptom complex (radiculopathy, neurogenic claudication, or mechanical back pain). Stenosis can also be classified radiographically, by the location of the stenosis (for example, central canal, lateral recess, or intervertebral foramen) or by the presence of deformity such as spondylolisthesis or scoliosis. Overlap occurs in these schemes of classification in that central stenosis with thecal sac compression typically leads to neurogenic claudication, whereas lateral recess compression is associated with compression of an individual nerve root and, therefore, radiculopathy. Because radiographic changes associated with stenosis are very common with aging, understanding the pathophysiology of lumbar spinal stenosis is critical in the assessment and management of related symptom complexes. Although symptoms may arise from narrowing of the spinal canal, not all patients with narrowing develop symptoms. The reason why some patients develop symptomatic stenosis and others do not is still unknown. Therefore, the term lumbar spinal stenosis refers not to the pathoanatomic finding of spinal canal narrowing, but rather to a clinical syndrome of lower extremity pain caused by mechanical compression on the neural elements or their blood supply.