Neurosurgery notes/Spine/Deformity/Craniocervical deformity/Central pillar condition/Congenital anomalies of the posterior atlas arch

Congenital anomalies of the posterior atlas arch

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Central pillar condition
 

General

  • Relatively common anomalies.
  • Should not be confused with Currarino triad (an inherited congenital disorder of the sacrum and anus or rectum).

Numbers

  • Incidence 0.7-3%

Clinical presentation

  • Highly variable
  • Most asymptomatic and incidental
  • Severe symptoms
    • intermittent tetraparesis after minor cervical trauma have been described
    • Not surprisingly, higher morphological groups (especially C and D, owing to a posterior tubercle) tend to be symptomatic, either post-trauma or intermittent to chronic.
    • For example, symptoms due to impingement of the cord by a posterior tubercle during extension
    • Post-traumatic symptoms have been described in the milder forms

Classification

  • Currarino 1994: a combination of morphology and clinical presentation
      • Morphological types
        • type A: failure of posterior midline fusion of the two hemiarches
        • type B: unilateral defect
        • type C: bilateral defects
        • type D: absence of the posterior arch, with persistent posterior tubercle
        • type E: absence of the entire posterior arch, including the tubercle
      • Clinical subgroups
        • 1: incidental imaging finding, asymptomatic
        • 2: neck pain or stiffness after trauma to the head or neck
        • 3: chronic symptoms referable to the neck
        • 4: various chronic neurological problems
        • 5: acute neurological symptoms following minor cervical trauma
      notion image
  • Type A and subgroup 1
    • commonest (approximating 80% of cases)
    • encountered in 4% of the general population
  • All other morphological types (B to E) are encountered in only 0.69% of the population

Pathology

  • Embryology
    • A developmental failure of chondrogenesis (lack of chondrification).
    • In the embryological period C1 is usually formed from three primary ossification centres:
      • an anterior centre developing into the anterior tubercle
      • two lateral centres giving rise to the lateral masses and posterior arch
    • ~2% of the population, an additional ossification centre develops in the posterior midline, subsequently forming into a posterior tubercle.
    • During ossification different anomalies can develop, comprising:
      • Median cleft(s) of the posterior arch
      • Varying degrees of posterior arch dysplasia
      • Either with or without the presence of posterior tubercle (see above)
    • Fusion of ossicles usually occurs during age 3 to 5 years.
      • Incomplete posterior fusion may even be normal in children up to 10 years old.
  • Mechanism
    • A reduced distance between occiput and spinous processes in extension causes spinal cord compression by inward buckling of the ligaments and that this is a possible mechanism of acute or chronic injury.
    • Secondary hypertrophy of the ligaments and dura due to a partial or complete absence of the posterior arch causing cord compression

Associations

  • Arnold-Chiari malformation
  • gonadal dysgenesis
  • Klippel-Feil syndrome
  • Down syndrome
  • Turner syndrome

Treatment and prognosis

  • For asymptomatic cases, no treatment or follow-up is needed, as considered a benign anatomical variant.
  • avoid contact sports
    • patients with type C and D
  • In cases with symptomatic compression, surgery with excision of the posterior arch is considered curative