MR evaluation of epidural fibrosis: Proposed grading system with intra- and inter-observer variability

The purpose of this study is to present a grading system for the Magnetic R esonance (MR) appearance of epidural fibrosis, and to present the inter- an d intra-observer variability of the system. The study population was from a randomized, double blind, controlled multicenter clinical trial evaluating the safety and effectiveness of ADCON(R)-L anti-adhesion barrier gel, in p reventing epidural fibrosis and dural adhesions following single-level unil ateral laminectomy/discectomy for lumbar disc herniations. MRI of the lumba r spine was obtained, without and with gadolinium enhancement, pre-operativ ely and at six months postoperatively. Patients having extensive epidural s car have been shown to be 3.2 times more likely to experience recurrent rad icular pain than those patients with less extensive epidural scarring. New agents have appeared in the marketplace and in clinical trials that maybe u sed intra-operatively to modulate the presence or absence of epidural scar tissue. Given these factors, the need to accurately describe the location a nd amount of epidural scar tissue has assumed more pressing importance. Two readers, blinded to clinical findings and to the other reader, independent ly evaluated the MR examinations in 50 postoperative lumbar spine surgery p atients using the previously defined categorization of epidural scar for fi ve levels in each patient, four quadrants per level. In addition, 114 exami nations were separately evaluated by the same reader for evaluation of intr a-observer variability. For the purposes of epidural fibrosis identificatio n, only the axial T1-weighted images with and without contrast were utilize d. The amount of epidural fibrosis was graded on a scale of 0-4 for each qu adrant at each imaging slice encompassing the operative level: 0= no/trace scar; 1 = > 0% and less than or equal to 25% of quadrant filled with scar; 2 = > 25% and less than or equal to 50% of quadrant filled with scar; 3 = > 50% and less than or equal to 75% of quadrant filled with scar; 4 = > 75% and less than or equal to 100% of quadrant filled with scar. Each reader ev aluated a total of 1000 epidural quadrants for the inter observer assessmen t The estimated kappa(w) index is 0.68 with 95% confidence interval (CI) of [0.64, 0.77]; this is substantial agreement There were a total of 2,280 qu adrants evaluated overall for the intra-observer assessment. The estimated Ic, index is 0.94 with 95% CI of [0.93, 0.95]; this is almost perfect agree ment Substantial intra-observer and near perfect inter-observer agreement w as achieved for evaluation of epidural scar using a relatively simple, semi -quantitative approach to the T1-weighted axial MR images. A standard gradi ng system for epidural scar is proposed.