What does a disc extrusion on a lumbar computed tomography (CT) scan mean?

Understanding Disc Extrusion on Lumbar CT Scan

A disc extrusion on a lumbar CT scan indicates a severe form of disc herniation where the nucleus pulposus has broken through the annular fibers and extruded into the spinal canal, potentially causing nerve compression and associated neurological symptoms.

What Is Disc Extrusion?

Disc extrusion represents an advanced stage of disc herniation with specific characteristics:

• The disc material has broken through the outer annular fibers
• The extruded material may migrate up or down the spinal canal
• It appears as a lobulated soft tissue mass on CT, often 6mm or more from the parent disc 1
• The extruded material can sometimes become a free fragment separate from the parent disc
• In rare cases, calcification of the extruded material may occur

CT vs. MRI for Disc Extrusion Evaluation

While your question specifically asks about CT findings:

• CT shows disc extrusion as a soft tissue mass with similar attenuation to the disc space 1
• CT is excellent for detecting bony pathology but less sensitive for soft tissue details
• MRI is superior for evaluating disc pathology, including extrusions, due to better soft tissue contrast 2
• MRI more accurately depicts nerve root compression and can evaluate for cord compression 2

Clinical Significance and Implications

Disc extrusions often have more significant clinical implications than other disc abnormalities:

• Potential for nerve compression: Extruded disc material can compress nerve roots, causing radiculopathy (radiating pain, numbness, weakness in a nerve distribution)
• Cauda equina risk: Large central extrusions can compress multiple nerve roots and potentially cause cauda equina syndrome, a surgical emergency 2
• Natural history: Studies show that disc extrusions can spontaneously resolve in many patients (up to 75%) when treated non-operatively 3
• Surgical considerations: The location of extrusion (central vs. far lateral) affects surgical approach if intervention is needed 4

When Further Evaluation Is Needed

If a disc extrusion is identified on CT, consider:

1. MRI evaluation: For better soft tissue detail and to assess nerve compression

   • MRI without contrast is typically sufficient for initial evaluation 2
   • MRI with contrast may be helpful if there's concern for infection, inflammation, or to distinguish recurrent disc from scar tissue in post-surgical patients 2

2. Neurological assessment: Evaluate for signs of nerve root compression or cauda equina syndrome

   • Motor/sensory deficits
   • Bladder/bowel dysfunction
   • Saddle anesthesia

Management Considerations

Management depends on clinical presentation:

• Conservative management is often appropriate for most disc extrusions without severe neurological deficits
• Surgical intervention may be indicated for:
  • Progressive neurological deficits
  • Cauda equina syndrome
  • Intractable pain despite conservative management
  • Large extrusions causing significant compression

Important Caveats

• Imaging findings must be correlated with clinical symptoms, as asymptomatic disc abnormalities are common 2
• CT may miss some soft tissue details that could be important for treatment planning
• The presence of disc extrusion on imaging does not automatically indicate need for surgery
• Follow-up imaging may be warranted to assess for spontaneous resorption in patients managed conservatively

Remember that disc extrusion represents one point on a spectrum of disc pathology, and treatment decisions should be based on both imaging findings and clinical presentation.