Neurosurgery Department, University General Hospital of Alicante, Foundation for the Promotion of Health and Biomedical Research in the Valencian Region (FISABIO), Alicante, Spain
Lumbar foraminal stenosis is defined as the narrowing of the bony exit of the nerve root caused by a decrease in the height of an intervertebral disk, osteoarthritis in the facet joints, cephalad subluxation of the superior articular process of the inferior vertebra, and buckling of the ligamentum flavum or protrusion of the annulus fibrosus.
Nerve root compression was evident in twenty-one of the 100 foramina, in eight of the ten foramina in which the posterior disc height was four millimeters or less, and in four of the five foramina in which the foraminal height was fifteen millimeters or less. These critical dimensions may be indicators of lumbar foraminal stenosis. However, compression of a spinal nerve root does not always cause sciatica, and the clinical findings must always be taken into account when a diagnosis of stenosis is considered 1).
A correlation between curve types and symptomatic foraminal stenosis exists. Adult scoliosis patients with sciatic nerve pain typically present with foraminal stenosis at the concavity of the caudal fractional curve. Similarly, patients with femoral nerve pain present with foraminal stenosis at the concavity of the caudal fractional curve when the main structural curve is thoracic, thoracolumbar, or lumbar (apex L2 or higher) 2).
Lumbar degenerative disc disease
In the majority of patients, lumbar stenosis is caused by degenerative deterioration in the spine due to aging.
Typically, it will produce symptoms that affect one side of the body – as each vertebra has two foramina (one foramen on either side), and often, only one of those openings will be narrowed. In some cases, bilateral foraminal stenosis develops, which means both vertebral foramina are constricted and both sides of the body experience symptoms.
Because lumbar foraminal stenosis manifests in the lower back, symptoms will appear in that region, such as radial pain, or radiating pain, that travels from the lumbar region to the hips, buttocks and the back of one leg. Issues pertaining to numbness, tingling, weakness or cramping also can occur. In cases of severe foraminal stenosis, patients may experience bladder or bowel dysfunction, which could indicate a medical emergency called cauda equina syndrome.
Ohba et al., demonstrates combination of conventional imaging techniques, to improve the detection of symptomatic foraminal stenosis.
Measurement of the foraminal width and height on CT imaging of the diseased side was significantly less than that on the intact side in the LSFS group. The grading scale for facet joint arthritis on the diseased side was significantly higher than that on the intact side in the LSFS group. The prevalence of the vacuum phenomenon and stage of intervertebral disk (IVD) pathology were higher in the L5-S1 spine of the LSFS group (95.2%) compared with the lumbar spinal canal stenosis (LCS) group (21.1%). MRI study revealed that the prevalence of Type 3 Modic changes was significantly higher in the LSFS group (39.3%) compared with the LCS group (7.7%) 3).
Although magnetic resonance imaging (MRI) is widely used, and is considered by many as an appropriate tool for studying spine pathologies, there is limited data to suggest that MRI examinations are sufficiently sensitive or specific for the diagnosis of LSFS.
There is no widely used diagnostic criterion or grading system for lumbar foraminal stenosis on MRI. For clinical studies with the objective of comparing different therapeutic methods for lumbar foraminal stenosis, an adequate grading system that has good reproducibility is necessary. In addition, in daily routine practice, a grading system for lumbar foraminal stenosis is necessary for writing radiologic reports.
There have been few reports on the grading or classification of lumbar foraminal stenosis on MRI 4) 5). The grading system suggested by Wildermuth et al. 6) focused on only the degree of epidural fat obliteration. The classification of lumbar foraminal stenosis proposed by Kunogi and Hasue 7) included the anteroposterior, cephalocaudal, and circumferential types without stenosis grade. The grading system of Wildermuth et al. and the classification proposed by Kunogi and Hasue do not consider direct nerve root compression or deformity, which may be important.
Effective foraminal height, effective superior foraminal width and the effective ratio can regard as the main evaluation index for LPS in parasaggital MRI finding 8).
In patients with developmental or combined stenosis of the central spinal canal, a concomitant foraminal stenosis is likely to be present, or at least should be suspected 9).
In a T1 MRI the normal is appearance with white fat signal surrounding the exiting nerve roots.
In stenotic (narrowed), there is no fat surrounding the nerve.
The association between disc pathology and facet osteoarthrosis can cause occult foraminal stenosis. Strategies to image the spine under physiological load conditions may improve the clinical diagnosis of radicular pain 10).