Lumbosacral epidural lipomatosis: MRI grading

Abstract

Lumbosacral epidural lipomatosis (LEL) is characterized by excessive deposition of epidural fat (EF). The purpose of our retrospective study was to quantify normal and pathologic amounts of EF in order to develop a reproducible MRI grading of LEL. In this study of 2528 patients (1095 men and 1433 women; age range 18-84 years, mean age 47.3 years) we performed a retrospective analysis of MRI exams. We obtained four linear measurements at the axial plane parallel and tangent to the superior end plate of S1 vertebral body: antero-posterior diameter of dural sac (A-Pd DuS), A-Pd of EF, located ventrally and dorsally to the DuS, and A-Pd of the spinal canal (Spi C). We calculated (a) DuS/EF index and (b) EF/Spi C index. We developed the following MRI grading of LEL: normal, grade 0: DuS/EF index >or=1.5, EF/Spi C index <or=40%; LEL grade I: DuS/EF index 1.49-1, EF/Spi C index 41-50% (mild EF overgrowth); LEL grade II: DuS/EF index 0.99-0.34, EF/Spi C index 51-74% (moderate EF overgrowth); LEL grade III: DuS/EF index <or=0.33, EF/Spi C index >or=75% (severe EF overgrowth). The MRI exams were evaluated independently by three readers. Intra- and interobserver reliabilities were obtained by calculating Kappa statistics. The MRI grading showed the following distribution: grade 0, 2003 patients (79.2%); LEL grade I, 308 patients (12.2%); LEL grade II, 165 patients (6.5%); and LEL grade III, 52 patients (2.1%). The kappa coefficients for intra- and interobserver agreement in a four-grade classification system were substantial to excellent: intraobserver, kappa range 0.79 [95% confidence interval (CI), 0.65-0.93] to 0.82 (95% CI, 0.70-0.95); interobserver, kappa range 0.76 (95% CI, 0.62-0.91) to 0.85 (95% CI, 0.73-0.97). In LEL grade I, there were no symptomatic cases due to fat hypertrophy. LEL grade II was symptomatic in only 24 cases (14.5%). In LEL grade III, all cases were symptomatic. A subgroup of 22 patients (42.3%) showed other substantial spinal pathologies (e.g., disk herniation). By means of simple reproducible measurements and indexes MRI grading enables a distinction between mild, moderate, and severe EF hypertrophy. Kappa statistics indicate that LEL can be reliably classified into a four-grade system by experienced observers.

Idiopathic Thoracic Epidural Lipomatosis with Chest Pain

“…In approximately 75% of SEL, this may be secondary to exogenous steroid ad- . Diagnosis is best based on MRI 6,10,15) . T1-WI differentiate epidural fat from dural content with a high degree of specificity and allow for measurement of adipose tissue thickness.…”

“…T1-WI differentiate epidural fat from dural content with a high degree of specificity and allow for measurement of adipose tissue thickness. Definite MRI finding of SEL is the pathognomonic appearance of fat on MRI; high signal intensity on T1-WI, intermediate signal intensity on T2-WI 2,6,9,10,15) . On CT scans, SEL presents as a homogenous hypodense epidural mass with a density between -80 and -160 HU 24) .…”

“…On CT scans, SEL presents as a homogenous hypodense epidural mass with a density between -80 and -160 HU 24) . Several grading system by MRI were reported but could not show correlation with clinical symptoms 6,10,15,16,21) . The mean sagittal thickness of the epidural fat in these studies was 4.6 mm with a normal range of 3 to 6 mm.…”

“…Haddad, et al 12) first hypothesized that idiopathic SEL was a byproduct of obesity, with the gradual overgrowth of epidural fat resulting in compression of the spinal cord and nerves. Thereafter, several researchers asserted that the term 'idiopathic' should be used solely to characterize cases of SEL that develop in non-obese patients, who were not receiving corticosteroid therapy, and without any other underlying SEL-related disease such as hypothyroidism or endogenous corticosteroid production 4,6,9,19) . About 16 cases of idiopathic SEL in non-obese patients were reported previously 1,9) .…”

Does abdominal obesity cause increase in the amount of epidural fat?

“…Borre et al [4] indicated that 86.6% of lipomatosis cases are obese (BMI [ 27.5). In the epidural lipomatosis cases that are seen with obesity, epidural fat can be reduced by low calorie diets [5,13]. But the significant existence of obesity in advanced lipomatosis cases was not determined yet.…”