Diagnostic Value Of The Epidural Fat Deposition Sign For Pars Interarticularis Defect

Part 1. Diagnostic Value of the Epidural Fat Deposition Sign for Occult Pars Interarticularis DefectObjective:The purpose of this study was to observe the diagnostic value of the epidural fat deposition sign in MRI for occult pars interarticularis defect, and to discuss the its mechanism.Methods:X-ray, CT and MRI images of the lumbar spine checked in Sir Run Run Shaw Hospital were retrospectively analyzed. Cases of positive epidural fat deposition sign were observed. All the patients’clinical data were recorded, including sex, age, clinical symptoms and signs, relevant past history and imaging diagnosis. The epidural fat and the detection of X-ray radiograph, intervertebral disc CT scan and MRI were systematically observed. The diagnostic value of the epidural fat deposition sign for occult lumbar spondylolysis was evaluated.Results:10 cases (7 males and 3 females) of positive epidural fat deposition sign were observed.7 of the cases were diagnosed lumbar pars interarticularis through surgery or radiological gold standard. According to the MRI grading of epidural fat,2 cases were Grade Ⅰ,1 was Grade Ⅱ and 3 were Grade Ⅲ. None of the pars interarticularis defects were detected by lumbar spine X-ray radiographs,1 was detected by intervertebral disc CT scan and 2 were detected by MRI were no signs of the isthmus bone fracture.2 of the 10 cases were diagnosed spinal epidural lipomatosis, both of whom had clinical symptoms of lower back pain and spinal stenosis findings in MRI.1 of the 10 cases had slight epidural lipomatosis but no significant spinal stenosis or clinical manifestation. All the pars interarticularis of the 3 cases were intact confirmed by CT sagittal reconstruction.Conclusion:The epidural fat deposition sign has a certain specificity for occult pars interarticularis defect. It can improve the diagnostic value of MRI for pars interarticularis defects in early stage as an indirect sign. In addition to pars interarticularis defects, the epidural fat deposition sign can be observed in spinal epidural lipomatosis. The two diseases can be differential diagnosed through past history, segments involved, associating with spinal stenosis, epidural fat characteristics presented in MRI.Part 2. Diagnostic Value of the Epidural Fat Deposition Sign for Isthmic SpondylolisthesisObjective:The purpose of this study was to evaluate the diagnostic value of epidural fat deposition between the dura mater and spinous process, namely "the epidural fat deposition sign" as an indirect sign of isthmic spondylolisthesis on mid-sagittal MR imaging of the lumbar spine.Methods:80 cases of isthmic (Group A) or degenerative (Group B) spondylolisthesis confirmed with conventional radiography or CT scan were respectively randomly collected. Another age and sex matched 40 cases without pars interarticularis defects or spondylolisthesis were collected as the control group (Group C). For each group, the sagittal canal ratio, defined as the maximum anteroposterior diameter of the canal at that level divided by the diameter of the canal at LI, was calculated and compared between the groups. Midline sagittal T1 weighted imaging MR images of the lumbar spine were reviewed to note the presence or absence of the epidural fat deposition sign and the spinal process sign. Logistics model was built to predict the probability for individuals. The ROC curves were analyzed to calculate the specificity and sensitivity of the epidural fat deposition sign alone, or combined with other indirect signs, for isthmic spondylolisthesis diagnosis.Results:The epidural fat deposition sign was noted in 65 out of 80 isthmic spondylolisthesis cases (81.3%),3 out of 80 degenerative spondylolisthesis cases (3.8%) and 1 of 40 control group cases (2.5%). The difference was statistically significant (P<0.01). This sign has an accuracy of 90.5%, sensitivity of 81.3%, specificity of 96.7%, positive predictive value of 94.2% and negative predictive value of 88.5% for diagnosis of isthmic spondylolisthesis. Compared with the epidural fat deposition sign alone, the combined sign contributes a significant higher sensitivity of 92.5% and specificity of 98.8% in the diagnosis of isthmic spondylolisthesis (P<0.05).Conclusion:The epidural fat deposition sign is a reliable indirect sign to diagnosis isthmic spondylolisthesis on mid-sagittal MR imaging of the lumbar spine. This sign could be useful for distinguishing degenerative from isthmic spondylolisthesis when degenerative sclerosis in the pars interarticularis mimics spondylolysis, when direct axial imaging of the pars interarticularis has not been done, or when imaging is technically inadequate.