Tethered cord

Findings

On the spinal ultrasound, the conus medullaris is abnormally positioned at the lower endplate of the L3 vertebral body level. The filum is prominent in size on ultrasound. The skin tag is confined to the subcutaneous level. The lumbar spine MRI demonstrates the conus at the same L3 level with blunting of the conus tip and thickening of the filum. Incidental note is made of a transitional vertebral body. Again, the skin tag appears confined to the subcutaneous level.

Differential Diagnosis:
- Tethered cord
- Normal variant low-lying conus
- Open or closed spinal dysraphism
- Post-surgical low-lying conus


Diagnosis: Tethered cord


Key points

Tethered cord occurs when the distal spinal cord does not completely involute and the conus improperly ascends. The stretching of the cord may result in vascular compromise.
Best demonstrated as a conus lying below the inferior endplate of the L2 vertebral body. (Normal conus medullaris tip position is at L4-5 at 16 weeks gestation, at L2-3 at birth, and then generally resides at L1-2 after 3 months of age.)
Associated with imperforate anus, diastematomyelia, filar lipoma, and filar cysts. Also, patients may demonstrate muscle atrophy, gait problems, orthopedic issues, bladder dysfunction, and may have hair patches or dermal sinus tracts.
Affects females more often than males (3:2).
On MRI, may see prolonged T1 relaxation in the cord that could represent hydromyelia or myelomalacia. Look for a thick and shortened filum terminale.
The tethered cord must meet criteria of position (below L2 at age 12 and below L3 at birth). The cord does not freely move on cine imaging, and the nerve roots may have an aberrant course. The cord may be fused to vertebral arches.
The tight filum measures more than 2mm at the L5-S1 level. May see associated cysts or lipomas on ultrasound or MRI.
On imaging, look for vertebral body abnormalities like scoliosis, spina bifida, and increased interpedicular distance.
Treated with decompressive laminectomy, removal of lipomas, untethering the spinal cord.