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:
- Primary neural developmental defect.
- 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
Login to Read More
