Anterior epidural fat as a diagnostic marker on magnetic resonance imaging for differentiating isthmic and degenerative lumbar spondylolisthesis: a retrospective study.

Abstract

Retrospective study. To investigate the diagnostic utility of anterior epidural fat (EF) for distinguishing isthmic from degenerative lumbar spondylolisthesis. Isthmic and degenerative lumbar spondylolisthesis must be distinguished accurately for appropriate clinical decision making. However, magnetic resonance imaging (MRI) often fails to detect pars defects; thus, additional imaging markers are needed. We retrospectively analyzed lumbar spondylolisthesis in 274 patients, of whom 129 had isthmic disease and 145 had degenerative disease. We assessed the presence and structure of anterior EF on midsagittal MRI, calculated diagnostic performance metrics, and used multivariable logistic regression to identify independent predictors of isthmic spondylolisthesis. Anterior EF was observed in 95.3% of isthmic cases and 28.3% of degenerative cases (p <0.001). As a diagnostic marker, anterior EF had 95.3% sensitivity and 71.7% specificity, and the area under the receiver operating characteristic curve indicated excellent discriminative ability. Morphologically, acute triangular anterior EF was significantly more common in patients with isthmic disease (75.2%) than in those with degenerative disease (17.2%). Multivariable analysis confirmed anterior EF as a strong independent predictor (odds ratio, 38.730; p <0.001). Anterior EF is an MRI feature that is highly sensitive and moderately specific for identifying isthmic spondylolisthesis. Its presence and characteristic acute triangular structure are valuable ancillary signs that are useful in early, noninvasive diagnosis.