What is the management plan for a newborn with a low-lying conus (cauda equina) terminating below L2-L3 on ultrasound?

Management of a Newborn with Low-Lying Conus Medullaris Below L2-L3 on Ultrasound

A low-lying conus medullaris terminating below L2-L3 on ultrasound in a newborn is radiographically consistent with tethered cord, but clinical follow-up without additional imaging is appropriate in the absence of other neurological findings or cutaneous markers.

Understanding Normal Conus Medullaris Position

The conus medullaris (CM) is the tapered lower end of the spinal cord. According to established guidelines:

• By 2 months after birth, the CM normally ends at the L1-L2 disc space 1
• The lowest normal level (95% confidence limits) is the middle third of the L2 vertebra 1
• A CM that ends below the middle third of L2 is radiographically considered tethered 1

Clinical Significance of Low-Lying Conus

The position of the conus medullaris has developmental implications:

• During fetal development, the spinal cord ascends relative to the vertebral column
• A low-lying conus may represent incomplete ascent or tethering
• A CM that appears below mid-L2 level should be considered potentially tethered 2

Assessment Algorithm for Low-Lying Conus

Step 1: Evaluate for Associated Findings

• Examine for cutaneous markers (dimples, hair tufts, hemangiomas, lipomas)
• Check for neurological abnormalities of lower extremities
• Assess for anorectal or genitourinary malformations
• Look for foot abnormalities

Step 2: Risk Stratification

• Low risk: Isolated finding without cutaneous markers or neurological deficits
• High risk: Presence of cutaneous markers, neurological deficits, or other congenital anomalies

Step 3: Management Based on Risk

• For low-risk newborns:

  • Clinical follow-up for developmental milestones
  • No immediate additional imaging needed
  • Reassure parents about favorable prognosis

• For high-risk newborns:

  • Referral to pediatric neurosurgery
  • MRI of the spine (without and with contrast)
  • More intensive neurological monitoring

Evidence Supporting Conservative Management

Research evidence strongly supports a conservative approach for isolated low-lying conus:

• In a study of 748 spinal sonograms, isolated borderline low conus was found in 12% of infants 3
• Follow-up of 50 children with isolated borderline low conus showed normal motor milestones in all cases 3
• Follow-up imaging in 11 children showed normalization of conus position in 10 cases 3

Important Considerations

1. Terminology clarification: A CM below L2-L3 is radiographically tethered but may not lead to clinical tethered cord syndrome 1

2. Tethered cord syndrome refers to clinical deterioration resulting from spinal cord tethering, which involves physical stretching of the spinal cord leading to impaired blood flow and neurological dysfunction 1

3. Avoid unnecessary imaging: Additional imaging studies expose the infant to potential risks:

   • MRI may require sedation, which carries risks for brain development in children under 3 years 1
   • Radiation exposure from CT should be avoided when possible 1

4. Monitoring approach: Focus on developmental milestones, particularly gross motor skills

When to Consider Additional Imaging

MRI should be considered if:

• Neurological symptoms develop
• Cutaneous markers of spinal dysraphism are present
• Associated structural abnormalities are suspected
• Failure to meet developmental milestones

Conclusion

For a newborn with an isolated finding of low-lying conus medullaris below L2-L3 on ultrasound, clinical follow-up without additional imaging is the most appropriate management strategy. Parents should be educated about monitoring developmental milestones and signs that would warrant reassessment.