Dysraphism of the Posterior (Spinal) Neural Tube

  • Located posterior to the point of initial neural tube closure (below the foramen magnum).

Terminology and Definitions

  • Spinal Dysraphism: A broad spectrum of anomalies involving variable degrees of non-fusion of neural, vertebral, and mesenchymal tissues.
  • Spina Bifida: Specifically refers to incomplete bony vertebral closure around the spinal cord.
  • Dysraphic lesions categorized based on skin coverage:
    • Open Dysraphism: Not skin-covered (e.g., myelomeningocele, myeloschisis).
    • Closed Dysraphism: Skin-covered lesions (e.g., meningocele, lipomeningocele).

    Open Spinal Dysraphism (OSD)

    Pathophysiology

    • Occurs due to regional failure of neural tube closure (~3rd week of gestation).
    • Fundamental defect: Non-disjunction of neural and cutaneous ectoderm.
    • Prevents mesenchyme from separating neural tube from skin, thus impeding vertebral development.
    • Results in exposure of ependymal-lined central canal (placode) to external environment.

    Types of Open Dysraphism

    • Myeloschisis (Myelocele):
      • Placode flush with skin surface.

      Pathogenesis: Two-Hit Hypothesis

      • Neural tissue displaced dorsally by expanded anterior subarachnoid space.
      • Placode protrudes externally beyond skin level.

      Epidemiology

      • Neurological deficits result from:
        1. Primary neural developmental defect.
        2. Secondary damage from amniotic fluid exposure (chemical, inflammatory, physical insults).

      Aetiological Factors

      • Incidence: ~0.5–1.0 per 1000 live births (regional variability).
      • Predominantly sporadic, multifactorial aetiology.

      Clinical Features and Associations

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      Information
      Published:30 April 2025
      Modified: 30 April 2025