Lumbar spinal stenosis (LSS) is common sequelae of degenerative disorders of spine. Spinal canal stenosis is a narrowing in the spinal canal or neural foramina, causing compression on the spinal cord, cauda equina, or individual nerve roots, and it may be congenital or acquired. The acquired causes for Spinal canal stenosis are frequently occurring and can result from: facet osteoarthritis, ligamentum flavum hypertrophy, degenerative bulging disc, or osteophyte formation.
The nerve root sedimentation (NRS) sign is a new radiological sign first reported by Barzet al.In the normal person during supine position, the nerve roots would sink posteriorly in the dural sac due to gravity. In those patients with LSS, the nerve root would not be able to sink but disperse ventrally. The NRS sign has been shown to discriminate well between patients with and without LSS and reported to be 94% sensitive and 100% specific. However, the sign is not widely used probably due to its limited reliability study. A positive sedimentation sign was defined as the absence of nerve root sedimentation in at least 1 axial MRI scan, at a level above or below, disregarding the location of the scan within the level and its proximity to the maximal stenosis.
The only exception from this is the two nerve roots leaving the dural sac one segmental level below the stenosis. If there are nerve roots in the ventral part of the dural sac except for the ones exiting the dural sac, the sedimentation sign is positive.