Sedimentation sign
Barz et al. 1) demonstrated for the first time in 2010 that in patients without lumbar spinal stenosis (LSS) a sedimentation of the nerve roots to the dorsal region of the dural sac in magnetic resonance images by gravitational force and defined its absence as a positive sedimentation sign.
A positive sedimentation sign was defined as the absence of sedimentation of the nerve roots at the level above and below the stenosis in at least one cross-section magnetic resonance image, irrespective of the level of the section and its proximity to the maximum stenosis. As a rule, the nerve roots usually settle into the dorsal region of the dural sac by gravity, which was defined as a negative sedimentation sign. The only exception are the two roots exiting the dural sac one level below the stenosis. If there are nerve roots in the ventral dural sac (apart from the exception mentioned above), the sign is positive.
Evidence
2015
Current evidence suggests that the sedimentation sign has high sensitivity and specificity for diagnosing severe lumbar spinal stenosis. Its performance in diagnosing moderate and mild spinal stenosis, however, has yet to be corroborated in properly designed studies 2).
A positive sedimentation sign was associated with a small but significantly greater surgical treatment effect for Oswestry Disability Index in patients with symptomatic LSS, after adjusting for other demographic and imaging features. These findings suggest that positive sedimentation sign may potentially be a useful adjunct to help guide an informed treatment choice regarding surgery for LSS 3).
2014
Patients with LSS have an increased epidural pressure at the level of the stenosis and altered pressure wave characteristics below. We argue that the absence of sedimentation of lumbar nerve roots to the dorsal part of the dural sac in supine position may be due to tethering of affected nerve roots at the level of the stenosis 4)
In patients commonly treated with decompression surgery, the sedimentation sign does not appear to predict surgical outcome. In nonsurgically treated patients, a positive sign is associated with more limited improvement. In these cases, surgery might be effective, but this needs investigation in prospective randomized trials (Australian New Zealand Clinical Trial Registry, number ACTRN12610000567022) 5).