Value Of Computed Tomography To Evaluate Morphololgy Of Lumbar Spinal Epidural Fat

Background:Spinal epidural lipomatosis(SEL)is one of the pathogenic factors of lumbar spinal stenosis,which is characterized by an excessive deposit of normal un-encapsulated adipose tissue in the epidural space causing compression of the spinal cord or the nerve roots.The underlying pathological mechanism of SEL is still unknown and diagnosis of SEL requires clinical suspicion,imaging evidence,and surgical evaluation as well.Imaging evaluation of severity of epidural fat overgrowth and spinal canal stenosis provides important guidance to clinical diagnosis and treatment.Magnetic resonance imaging(MRI)is considered as the most sensitive and specific imaging method to assess' epidural fatty tissue.However,its contraindications,such as medical device implantation,some metal implants or claustrophobia,limit its general application.Alternative imaging method is required for patients with certain MRI contraindications.Computed tomography(CT),which has high diagnostic value in spinal degenerative diseases such as spinal canal stenosis,intervertebral disc bulging or herniation and arthrosis,spinal trauma,spinal tuberculosis and spinal neoplasms,has been widely used in lumbar disorder evaluation.However,the value of CT scan in evaluating adipose tissue morphological characteristics in spinal canal is still lacking in systemic research.Moreover,previous studies on grading amounts of epidural fat mainly rely on MRI,and a reliable quantitative CT grading of epidural fat overgrowth is still lack.Objectives:1.Our purpose is to investigate the value of CT to evaluate morphologic features of spinal epidural fat by analyzing correlation and agreement between CT and MRI in measuring morphologic parameters of lumbar epidural fat and dural sac.2.Our purpose is to introduce a quantitative grading system to CT and to investigate the value of CT in quantitative assessment of lumbar epidural fat overgrowth compared to MRI.Study design:1.The study population consisted of 368 patients(173 female 195 male,age range 18-86 years)who admitted to our clinic that accepted both CT scan and MRI of lumbar spine within 4 weeks from July 2014 to July 2016 at the Sir Run Run Shaw Hospital of Zhejiang University.Of available levels,1221 CT scan images and matched MR images of lumbar intervertebral levels were included in this retrospective analysis.Sociodemographic characteristics,including age,gender,body height,body weight,BMI and main clinical findings were recorded.2.CT density values of epidural fat and periphery tissues at axial intervertebral levels,were measured to compare their density.Furthermore,morphologic parameters of epidural fat and dural sac at intervertebral planes were also measured on CT and MR images respectively:antero-posterior diameter of the epidural fat(A-Pd EF),antero-posterior diameter of the dural sac(A-Pd DuS),transverse diameter of the dural sac(Td DuS),cross-sectional area of the epidural fat(CSA EF),cross-sectional area of the dural sac(CSA DuS).Agreement between CT and MRI measuring these parameters was evaluated by difference analysis,correlation analysis and agreement analysis.3.EF/Spi C index and DuS/EF index were calculated based on A-Pd EF,A-Pd DuS and antero-posterior diameter of spinal canal(A-Pd Spi C)both on CT and MRI.Absolute quantity evaluation and relative quantity grading of epidural fat at each intervertebral plane were conducted and agreement between CT and MRI was evaluated.Finally,relationship between amounts of epidural fat and sociodemographic features of our study population was analyzed.Results:1.CT density values were significantly different among tissues constituting or surrounding lumbar spinal canal,epidural fat showed the lowest CT density values with at least a rmean difference of 100HU compared to other tissues(p<0.001).2.High positive linear corrections were detected between diameter and cross-sectional area of epidural fat or dural sac(CT:Pearson correlation coefficient r ranged from 0.608 to 0.914,p<0.001;MRI:r ranged from 0.661 to 0.923,p<0.001).3.Significant positive linear correlations were observed between CT and MRI measurements of A-Pd EF or CSA EF at all intervertebral levels(A-Pd EF:r = 0.738,0.770,0.783,0.780 and 0.873 from L1-2 to L5-S1 respectively,all p<0.001;CSA EF:Pearson correlation coefficient r=0.791,0.811,0.853,0.841 and 0.945 from L1-2 to L5-S1 respectively,all p<0.001).Bland-Altman plots depicted satisfied agreement between CT and MRI in both A-Pd EF and CSA EF measurements.4.Significant positive linear correlations were observed between CT and MRI measurements of A-Pd DuS,Td DuS and CSA DuS at all levels except for L5-S1(A-Pd DuS:Pearson correlation coefficient r ranged from 0.821 to 0.888,all p<0.001;Td DuS:r ranged from 0.691to 0.811;CSA DuS:r ranged from 0.812 to 0.898,all p<0.001).Bland-Altman plots showed good agreement between CT and MRI in A-Pd DuS,Td DuS and CSA DuS measurements at all disc levels.5.Well agreement was detected between CT and MRI in absolute quantity evaluation at all intervertebral levels,with ? coefficients varying from 0.62 to 0.81(all p<0.001).6.Relative quantity grading system of epidural fat was introduced to CT,and parameters of epidural fat and EF/Spi C index showed significant increasing tendency with increased grading level,while parameters of dural sac and DuS/EF index showed significant decreasing tendency.Intraobserver and interobserver agreements were 0.88?0.90(p<0.001)and 0.79?0.82(p<0.001)separately.7.Moderate agreement was detected between CT and MRI in radiologically relative quantity grading of epidural fat at all intervertebral levels,with ? coefficients varying from 0.44 to 0.62(all p<0.001).8.Multiple regression analyses revealed that age and body weight were significantly correlated to the amounts of lumbar epidural fat(p<0.001).Conclusions:1.CT is qualified enough for distinguishing epidural fat tissue from periphery tissues.2.A-Pd EF and A-Pd DuS were significantly positive linear correlated to CSA EF and CSA DuS respectively,which were effective measurements for epidural fat and dural sac respectively.3.Accuracy of diameter and area measurements of epidural fat and dural sac on CT were comparable to those on MRI at all intervertebral levels.4.High correlation and agreement was detected between CT and MRI in evaluating lumbar absolute quantity of epidural fat.5.Relative quantity grading system of lumbar epidural fat was first applied on CT as a practicable method.6.Ability of CT in evaluating relative amounts of lumbar epidural fat is comparable to MRI.7.Age and body weight were significantly correlated to the amounts of lumbar epidural fat.