Is conus medullaris (lower end of the spinal cord) compression a condition affecting the terminal portion of the spinal cord?

Conus Medullaris Compression: Definition and Clinical Significance

Yes, conus medullaris compression refers specifically to compression of the terminal portion of the spinal cord. The conus medullaris is the tapered, cone-shaped distal end of the spinal cord that typically terminates at the level of the L1-L2 vertebral disc space in adults 1.

Anatomical Considerations

The conus medullaris represents a critical anatomical transition zone where:

• The spinal cord proper ends in a tapered, cone-like structure
• Below this level, the spinal nerve roots continue as the cauda equina
• The filum terminale extends from the conus medullaris to the coccyx 2

By 2 months after birth, the conus medullaris normally ascends to end at the L1-L2 disc space, with the lowest normal position (95% confidence limits) being at the middle third of the L2 vertebra 1. A conus that ends below this level is considered radiographically tethered, though clinical correlation is required to determine if this causes tethered cord syndrome 1.

Clinical Manifestations of Conus Medullaris Compression

Compression of the conus medullaris can result in a distinct clinical syndrome with symptoms that may include:

• Back pain (local and/or radicular)
• Perineal or saddle anesthesia
• Bladder and bowel dysfunction (often early and prominent)
• Symmetric lower extremity weakness and sensory changes
• Sexual dysfunction 3, 4

Interestingly, some cases of conus medullaris syndrome may present without lower extremity involvement, making diagnosis challenging but possible through careful neurological examination 3.

Causes of Conus Medullaris Compression

Common causes include:

1. Traumatic injuries at the thoracolumbar junction 4
2. Disc herniations (including intradural disc herniations) 3, 5
3. Tumors (extradural, intradural extramedullary, or intramedullary) 1
4. Vascular malformations affecting the terminal spinal cord 5
5. Congenital anomalies including tethered cord syndrome 1, 6

Diagnostic Approach

MRI is the gold standard for evaluating conus medullaris compression:

• MRI without contrast can identify structural abnormalities affecting the conus 1
• MRI with contrast may be necessary when infection or neoplasm is suspected 1
• The entire lumbar spine must be imaged to properly evaluate the conus, filum terminale, and potential spinal dysraphism 1

It's important to note that a conus medullaris in normal position can still be pathologically tethered, causing symptoms despite normal radiographic appearance 6. Therefore, clinical correlation with imaging findings is essential.

Management Considerations

Management of conus medullaris compression depends on the etiology but generally follows these principles:

• Urgent decompression is indicated for acute compression to prevent permanent neurological damage 1
• Corticosteroids may be administered when spinal cord compression is suspected, even before radiographic confirmation 1
• Surgical intervention is required for:
  • Spinal instability
  • Bony retropulsion causing cord compression
  • Progressive neurological deterioration despite conservative management 1

Prognosis

The prognosis for patients with conus medullaris compression depends on:

1. Timing of intervention (earlier treatment generally yields better outcomes)
2. Degree of neurological deficit before treatment
3. Underlying cause of compression
4. Presence of comorbidities

Patients who are ambulatory at presentation generally have better outcomes than those who present with paralysis 1.

Key Pitfalls to Avoid

1. Delayed diagnosis: Symptoms of conus medullaris compression represent a medical emergency requiring prompt evaluation and treatment
2. Incomplete imaging: The entire lumbar spine must be imaged to properly evaluate the conus
3. Over-reliance on imaging alone: Clinical correlation is essential, as a normally positioned conus can still be pathologically tethered 6
4. Failure to recognize atypical presentations: Some cases may present without lower extremity symptoms 3

Understanding the anatomy, clinical presentation, and management principles of conus medullaris compression is essential for timely diagnosis and treatment to prevent permanent neurological damage.