Tethered Cord

Diagnosis Definition

• The conus medullaris (tapered end of the spinal cord) starts to ascend relative to the vertebral bodies during intrauterine development and reaches the typical adult level (L1-L3) by about three months of age
• The filum terminale is a fibrous extension of the pia mater that extends from the apex of the conus medullaris to the coccyx
• Tethered cord syndrome is a neurological disorder caused by tissue attachments that limit the movement of the spinal cord; it is a term most commonly used in reference to patients with a low-lying conus medullaris and a thickened filum terminale
• Primary tethered cord syndrome occurs as an isolated anomaly; secondary tethered cord syndrome occurs in the setting of other abnormalities such as myelo/lipo/meningocele, dermal sinus tract, diastematomyelia (split spinal cord), lipoma, thickened/tight filum terminale, trauma, and surgery
• The syndrome can present with cutaneous manifestations, foot and spinal deformities, leg weakness, low back pain, scoliosis, and incontinence

Imaging Findings

• Ultrasound is useful in the neonatal population; the lack of ossification of the posterior arch of the spine in normal infants and the presence of a bony defect in patients with spina bifida permit sonographic examination
• MRI is the imaging modality of choice for evaluating a tethered cord in older children, and can show the location of the conus medullaris (normally superior to L3), assess the thickness of the filum terminale (normally less than 2 mm in cross-sectional diameter), identify traction lesions, and show associated bony dysraphisms
• The filum can be thickened with fat (seen as T1 hyperintensity), fibrous tissue (T2 hypointensity), or both

KEY IMAGES

Pearls

• Although fibrolipomatous thickening of the filum is present in up to 5% of patents on MRI, the majority do not have symptoms of spinal cord tethering
• Although rare, patients with fibrolipomatous thickening of the filum can become symptomatic at any age

References

1. Raghavan N, Barkovich AJ, Edwards M, et al.  MR imaging in the tethered spinal cord syndrome.  AJR Am J Roentgenol.  1989; 152(4):843-852
2. Yousem D, Grossman R.  The Requisites: Neuroradiology.  3rd ed.  Philadelphia, PA: Mosby-Elsevier; 2010:279-320