Delving into the Anatomy of the Filum Terminale
The filum terminale is a fine, thread-like filament of connective tissue at the lower end of the spinal cord. It is an extension of the pia mater and acts as an anchor for spinal stability. Its structure is divided into two parts.
The Two Segments of the Filum Terminale
- Filum Terminale Internum (FTI): This upper, longer segment is inside the dural sac, surrounded by the cauda equina and cerebrospinal fluid. It extends about 15 cm from the conus medullaris to the level of the second sacral vertebra (S2).
- Filum Terminale Externum (FTE): Also called the coccygeal ligament, this shorter segment is outside the dural sac. At S2, the FTI is covered by dura mater and becomes the FTE, which attaches to the coccyx.
Embryological Origin and Composition
Developing from the caudal cell mass, the filum terminale is a remnant of the spinal cord's caudal portion. It primarily consists of fibrous tissue with some glial and ependymal cells. A healthy filum is usually less than 2mm in diameter and provides stability to the spinal cord.
The Filum Terminale and Tethered Cord Syndrome
An abnormal filum terminale can lead to Tethered Cord Syndrome (TCS), where the spinal cord is restricted and stretched by attachments. This stretching can cause neurological problems as the spine grows.
Causes of Tethered Cord Syndrome
- Fatty or Thickened Filum Terminale: The most common cause of TCS is an abnormally thick or fatty filum that limits spinal cord movement.
- Spinal Lipomas: Fatty tumors can tether the spinal cord if they involve the filum terminale.
- Other Spinal Abnormalities: Conditions like spina bifida, split cord malformations, or scar tissue can also cause tethering.
Symptoms of Tethered Cord Syndrome
TCS symptoms vary by age and can worsen with growth.
In infants and young children:
- Skin marks on the lower back like dimples or hair tufts.
- Foot deformities or leg length differences.
- Delayed motor skills.
- Bowel and bladder control problems.
In older children and adults:
- Back and leg pain that worsens over time.
- Numbness or weakness in the legs.
- Bladder or bowel issues.
- Scoliosis.
- Changes in walking.
Diagnosis and Treatment
Diagnosing filum terminale conditions involves clinical assessment and imaging, mainly MRI of the lumbosacral spine. MRI shows detailed views of the spinal cord and filum. Spinal ultrasound is used for screening in infants.
Comparison of Normal vs. Tethered Filum Terminale
| Feature | Normal Filum Terminale | Tethered Filum Terminale |
|---|---|---|
| Appearance on MRI | Thin, elastic, typically less than 2mm in diameter | Thickened (>2mm), often fatty, and less flexible |
| Position of Conus Medullaris | Ends at or above the L1-L2 interspace in adults | Located abnormally low (below L2) or under tension |
| Movement | Spinal cord moves freely within the dural sac | Restricted movement of the spinal cord |
| Elasticity | High elasticity allows for normal spinal cord movement | Reduced elasticity, causing constant traction on the spinal cord |
Surgical Untethering
Surgical untethering is the main treatment for symptomatic TCS caused by an abnormal filum terminale. This surgery releases the filum to allow the spinal cord to move freely. For a simple fatty filum, the procedure involves sectioning the filum. Recovery is needed after surgery. Early surgery, especially in children, helps prevent lasting neurological damage. Surgery can improve symptoms, but may not reverse all damage, like bladder or bowel problems.
Conclusion
The filum terminale, a small spinal structure, is essential for spinal cord function by providing stability. Abnormalities can cause neurological issues like Tethered Cord Syndrome. Recognizing these conditions is key for timely diagnosis and management, particularly in children. If symptoms like back pain, leg weakness, or bladder/bowel problems occur, especially in children, evaluation for a tethered spinal cord is recommended. For more information, consult resources like the National Institutes of Health website (https://www.ncbi.nlm.nih.gov/).
