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Intraoperative Epidural Pressure in Patients with Positive Vs. Negative Sedimentation Sign Undergoing Spinal Surgery

Introduction The nerve root Sedimentation Sign (SedSign) in transverse magnetic resonance imaging (MRI) has been shown to discriminate well between selected patients with and without lumbar spinal stenosis (LSS). Previously it was demonstrated that a positive SedSign appears to identify patients who are less likely to benefit from nonsurgical treatment. It is still unknown which potential mechanisms may be responsible for the absence of nerve root sedimentation in transverse MRI scans in cases of severe LSS. Aim of our study was to identify the pressure values causing a positive SedSign in patients undergoing spinal surgery for LSS. Materials and Methods We measured the intraoperative epidural pressure in five patients with LSS and a positive SedSign and in five patients without LSS and a negative SedSign. Epidural pressure was measured using a Codman catheter in prone position under radioscopy at different locations in the lumbar spinal canal. Results: Patients with a negative SedSign had a mean epidural pressure of 9 mm Hg (minimum 8, maximum 11 mm Hg) independent of the location of the measurement. Breath and pulse-synchronous waves accounted for 1 to 3 mm Hg. In patients with mono-segmental LSS and a positive SedSign, the epidural pressure above and below the stenosis was similar (8 and 9 mm Hg respectively; minimum 7, maximum 12 mm Hg). At the level of the stenosis, the mean epidural pressure was 23 mm Hg (minimum 21, maximum 26 mm Hg). Whereas cranial of the stenosis breath and pulse-synchronous wave could be demonstrated, this wave was absent below the stenosis. There was no significant correlation between the diameter of the spinal canal and the level of the stenosis. Conclusion We conclude that in patients with LSS as a consequence of the increased epidural pressure (1) lumbar nerve roots are tethered at the level of the stenosis inhibiting the sedimentation of these nerve roots to the dorsal part of the dural sac in supine position, and (2) no breath and pulse-synchronous wave below the stenosis can be detected. However, these findings need confirmation in larger patient samples. Future research is warranted investigating the correlation between an increased epidural pressure and the level of lumbar stenosis. I confirm having declared any potential conflict of interest for all authors listed on this abstract Yes Disclosure of Interest None declared Barz T, Melloh M, Staub LP, et al. Nerve root sedimentation sign-evaluation of a new radiological sign in lumbar spinal stenosis. Spine 2010;;35(8):892–897.