A lipoma or fibrolipoma of the filum terminale is a somewhat uncommon (4-6%) and usually incidental, asymptomatic finding on MRIs of the lumbar spine.
Best visualized on sagittal T1-weighted MRIs
T1-weighted MRI = hyperintense
T2-weighted MRI = hyperintense (though not nearly as obvious)
Can sometimes be associated with a low-lying and thickened conus in cases with clinical findings consistent with tethered cord syndrome.