Neurosurgery notes/Paediatrics/Developmental abnormalities/Craniospinal anomalies/Chiari 3

Chiari 3

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Craniospinal anomalies

General

  • An extremely rare condition
  • This malformation is rarely compatible with life.

Main feature

  • Herniation of posterior fossa contents (cerebellum, pons and medulla) through a spina bifida defect at the C1–C2 level (encephalocele).
  • Herniated contents is grossly abnormal and often non functioning
    • In the most severe presentations, the herniated tissue within the encephalocele can include the brainstem, occipital lobes, parietal lobes, dural venous sinuses, and subarachnoid spaces.
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notion image
notion image
Posterior vault encephalocele.A congenital defect allowing herniation of meninges and sometimes brain tissue through the posterior skull, typically between the lambda and the foramen magnum.
Posterior vault encephalocele.A congenital defect allowing herniation of meninges and sometimes brain tissue through the posterior skull, typically between the lambda and the foramen magnum.

Associated features

Hindbrain Displacement:

  • The displacement of the cerebellum, brainstem, and fourth ventricle extends into the cervical canal, frequently reaching the C3–C5 level or even more. The herniating tissue realizes a posterior cranial fossa (PCF) encephalocele through a bony defect.

Bony anomalies:

  • C-III is typically characterized by an undersized PCF
  • An enlarged foramen magnum.
  • Scalloping of the clivus.
  • Hypoplasia of the parietal bones and possible posterior cervical agenesis (missing posterior elements from C1 to C5).
  • Lückenshädel (thinning or erosion of the skull).

Intracranial anomalies

  • Medullary kinking.
  • Tectal beaking.
  • Callosum dysgenesis.
  • Colpocephaly.
  • Hydrocephalus, which is present in up to 88% of cases.

Associated Spinal Anomalies:

  • Syringomyelia is common, occurring in up to 70% of cases.
  • Associated anomalies may include Dandy-Walker malformation, Klippel-Feil syndrome, and split cord malformation.

Pathogenesis

  • The most advocated theory is that C-III results from a chronic escape of cerebrospinal fluid (CSF) at the occipito-cervical neural tube defect level. This leakage causes the underdevelopment of the cerebral ventricle and posterior cranial fossa.
  • Alternatively, the malformation may stem from a primary neuroectodermal defect resulting in abnormal neurulation and consequent PCF hypoplasia, or a primary mesodermal defect leading to bone deficiency.

Prognosis and Outcome

  • Mortality:
    • There is a high risk of spontaneous and surgical mortality (overall rate of 29%).
  • Negative Prognostic Factors:
    • These include stridor at birth, poor neurological status prior to surgery, large encephalocele, and hydrocephalus.
    • The amount of herniating brainstem is crucial; a better outcome is registered if the ectopia is less than 5 cm.
  • Long-term Sequelae:
    • Surviving children almost invariably experience developmental delay, motor deficits, lower cranial nerve deficits, and epilepsy.
    • These neurological issues are generally attributed to primary brainstem dysfunction or secondary damage from distortion and traction of the brainstem caused by the malformation.