Syn: Lipoma of the filum terminale, filar lipoma.
A relatively common benign finding on MR imaging of the lumbar spine, seen in ~ 5 % of cases.
On MRI the abnormality typically is thin and linear, extends over only few segments. Signal iso intense to fat on all pulse sequences may show chemical shift artefact on T2* GRE sequences. T1 and T2 hyperintens with signal supression on STIR.
In most cases is an incidental finding of no clinical significance. However it is considered as one of the causes in tethered cord syndrome and may be associated with tethered cord, where there is associated markedly thickened filum with low lying conus. Location and the size of fatty filum are considered as the important factors for Tethered cord syndrome. The thickened fatty filum terminale (more than 2mm) considered as one of the causes of the tethering. Fat in the filum may represent mesodermal cells that did not properly migrate to their normal position in the process of canalization. The presence of fatty tissue may alter the developmental properties of the filum and may predispose patients to cord tethering. Bursara et al. reported the correlation between the fat and the neural dysfunctions with MRI. They concluded that fat in the filum terminale within 13mm of the conus medullaris was most predictive of neurological deficits. And TCS in adults is caused by the anoxia due to over-stretching of the conus medullaris - See more at h:ttp://www.ispub.com/journal/the-internet-journal-of-spine-surgery/volume-3-number-1/fatty-filum-terminale-on-mri.html#sthash.5KQVStuW.dpuf
In asymptomatic patients, nothing need be done. Difficulty arises in patients who have some symptoms suggesting tethered cord syndrome, but whose conus terminates at a normal level. Controversy as to the benefits of division of a fatty filum in such patients exists.
Imagingwise there is little or no differential when signals of fat is confirmed, however other filum terminale lesions like paraganglioma of the filum terminale and myxopapillary ependymoma can be considered.