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Diagnostic Value of the Posterior Epidural Fat Pad Sign in Assessing Spondylolysis of the Lumbar Spine on MRI 2014

Category General Spine Thomas J. O'Neill, MD
Bryan Foley, MD
Luis Ramos-Duran, MD
Nassim Akle, MD
Purpose Spondylolysis is not always easily visualized on MR imaging of the lumbar spine. In the absence of correlative imaging, indirect signs are important in the detection of spondylolysis. In this study we evaluated the diagnostic value of the “epidural fat pat sign” on mid-sagittal T1 MR as an indirect indicator of spondylolysis. Materials & Methods A retrospective observational review of patients with spondylolisthesis identified on lumbar spine MRI was conducted. Of those, 193 patients with correlative CT, plain radiographs or obvious defect on sagittal T1 MR confirming the presence or absence of spondylolysis were selected. Qualitative assessment and measurement of interposed epidural fat between the dura and spinous process was assessed on mid-sagittal T1 sequences. Results We identified 59 of 193 patients with confirmed spondylolysis and spondylolisthesis. Qualitative assessment for the presence of an epidural fat pad in patients with spondylolisthesis was 72.9% (59.7 – 83.6 CI) sensitive and 76.9% (68.8 - 83.7 CI) specific for those with spondylolysis. The presence of the sign was 58.1% (46.1 - 69.5 CI) predictive of spondylolysis and the absence of the sign was 86.6% (79.1%, 92.1 CI) predictive of its absence. Measurement of the anteroposterior dimension of the epidural fat pad with a threshold of 2.3 mm improved the positive predictive value to 75.6%. Conclusion A posterior epidural fat pad at the level of lumbar spondylolisthesis is an indirect indicator of spondylolysis and the absence of an epidural fat pad most likely correlates with degenerative changes at that level rather than spondylolysis. The clinical utility of this sign may be limited in obese patient populations and the sign may be most useful in conjunction with other indirect signs of spondylolysis. References Sherif H, Mahfouz AE. Epidural fat interposition between dura mater and spinous process: a new sign for the diagnosis of spondylolysis on MR imaging of the lumbar spine. Eur Radiol. 2004 Jun;14(6):970-3. Epub 2004 Feb 6. PubMed PMID: 14767603. Saifuddin A, Burnett SJ. The value of lumbar spine MRI in the assessment of the pars interarticularis. Clin Radiol. 1997 Sep;52(9):666-71. PubMed PMID: 9313730. Ulmer JL, Mathews VP, Elster AD, Mark LP, Daniels DL, Mueller W. MR imaging of lumbar spondylolysis: the importance of ancillary observations. AJR Am J Roentgenol. 1997 Jul;169(1):233-9. PubMed PMID: 9207531. McCormick CC, Taylor JR, Twomey LT. Facet joint arthrography in lumbar spondylolysis: anatomic basis for spread of contrast medium. Radiology. 1989 Apr;171(1):193-6. PubMed PMID: 2928525. Johnson DW, Farnum GN, Latchaw RE, Erba SM. MR imaging of the pars interarticularis. AJR Am J Roentgenol. 1989 Feb;152(2):327-32. PubMed PMID: 2783509.