Fat in the filum terminale is not an infrequent occurence, seen in 4 – 6%, and is usually easily detected on MRI (especially T2* sequences, as a result of chemical shift artefact). It is usually an incidental finding of no clinical concern.
In some individuals however it is associated with spinal dysraphism, thickening of the filum terminale (>3mm) and tethering of the spinal cord.
Imaging findings:
CT:
If large enough then fat density (-90 to -30HU) can be seen below the level of the conus. If small, and depending on the quality of the CT scanner, the size of the patient, and the amount of quantum mottle, it may be inapparent.
MRI:
Signal follows that of fat.
– hyperintense on T1 and T2 FSE
– saturates on fat saturation sequences
– demonstrates chemical shift artefact
– no enhancement.
Differential diagnosis:
There is little DDx when the presence of fat is confirmed, however other filum terminale lesions can be considered only to be eliminated.
References
1. E Brown et al “Prevalence of incidental intraspinal lipoma of the lumbosacral spine as determined by MRI.” Spine. 1994 Apr 1;19(7):833-6.
2. K Koeller et al “Neoplasms of the Spinal Cord and Filum Terminale: Radiologic-Pathologic Correlation” RadioGraphics 2000; 20: 1721-1749.
3. JM Provenzale et al “Duke Radiology Case Review: Imaging, Differential” Published 1997 Lippincott Williams & Wilkins ISBN:0397516134
Credit: Dr Frank Gaillard
