Lipoma of the Filum Terminale

T1 sagittal image of the lumbar spine showing multiple osteoporotic collapsed vertebral bodies with elongated linier  wavy hyperintense intraspinal structure from the level of L2 to S1 consistent with filum terminale lipoma.

Axial T1 weighted image showing filum terminale lipoma as small intraspinal hyperintense dot (arrow).

Discussion:

Fat in the filum terminale is not an infrequent occurence, seen in 4 – 6%, and is usually easily detected on MRI (especially T1 sequences). 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.
Classification: Four patterns: 

1) fatty filum with descended conus medullaris and symptoms.

2) fatty filum with descended conus medullaris and no symptoms.

3) fatty filum with normal conus medullaris position and symptoms.

4) fatty filum with normal conus medullaris position and no symptoms

Imaging findings:

CT scan: If the lesion is large, seen as hypodense focus (fat density HU -90 to -30) below the level of conus. If it is  small may not be visible.

MRI: is modality of choice.

• Hyperintense on T1 and T2 FSE
• Saturates on fat saturation sequences
• Demonstrates chemical shift artefact
• No enhancement.

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.