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Anomalies of the base of the skull and spine are seen in 30–50 percent of patients with a Type I Chiari malformation. These anomalies include:

  • Basilar impression (compression of the upper part of the spine into the base of the skull with resultant compression of the brain stem)
  • Atlanto-occipital fusion (bony union of the first level of the spine to the base of the skull)
  • Atlanto-axial assimilation (partial bony union of the first and second levels of the spine)
  • Klippel-Feil deformity (congenital union or fusion of levels of the spine within the neck with possible associated maldevelopment of levels of the neck's spine)
  • Cervical spina bifida occulta (bony defect in a the posterior part of the spine)
  • Scoliosis—commonly seen when hydromyelia exists (in 16–80 percent of patients), especially in children with immature spines

There may be signs of brain stem dysfunction in some who have a Chiari malformation (10–47 percent). This occurs when the displaced tissue of the malformation compresses the lower part of the brain stem. The following problems may develop as a result:

  • Drop attacks (sudden loss of body muscle tone with collapse to floor)
  • Postural and cough headaches (majority of cases)
  • Dull, chronic headache involving back of head or neck
  • Paroxysmal, severe headache associated with a Valsalva maneuver (cough headache)
  • Visual disturbances from nystagmus (jerking of eyes when looking to right or left), oscillopsia (vertical bobbing of eyes) or diplopia (double vision)
  • Spasticity (muscle stiffness)
  • Sensorimotor deficits (abnormal body sensation and/or muscle strength)
  • Ataxia (difficulty with balance and coordination)
  • Dysarthria (difficulty talking)
  • Dysphagia (difficulty swallowing)

Cases have been reported of children with previously undiagnosed Chiari malformations sustaining injuries to the spinal cord with no obvious abnormality in the X-rays of their spine. Evaluation of children who have sustained a spinal cord injury should include an MRI scan of their spinal cord, which includes imaging of the base of the brain to rule out a Chiari malformation.

Chiari II Malformation

As stated previously, this malformation is part of a larger syndrome seen in children with myelodysplasia (spina bifida). This is frequently misunderstood, and many parents think their child has a Type II malformation in spite of the fact that they do not have a myelodysplasia. It is exceedingly unusual to have a Type II malformation without having myelodysplasia. While all children with myelodysplasia will have the Chiari malformation, only 9–21 percent will exhibit symptoms that warrant treatment. Those destined to exhibit symptoms will do so either early in infancy or later in childhood with the presentation and outlook differing for the two groups.

Infants who are destined to develop difficulties due to their Chiari malformation will do so after several weeks or months of relative normalcy. Their families will notice increasingly stridorous breathing or higher-pitched crying. There may be apneic episodes. Left to deteriorate, these infants will develop dysphagia with associated nasal regurgitation and aspiration. They will appear very uncomfortable and prefer to assume a position with their head and back arched posteriorly with the head tilted to one side. Deterioration will progress rapidly from this point.

Treatment of infants with this condition is controversial. The first question to be answered is whether the shunt is malfunctioning; if it is, these symptoms can rapidly be reversed with correction of the shunt's functioning. If the symptoms are due to the Chiari malformation, however, treatment becomes more difficult and controversial, because it is particularly difficult in infants to differentiate symptoms due to mechanical compression of the lower brain stem from symptoms due to an untreatable malformation of the lower brain stem. Additionally, an abnormally formed brain stem that is marginally functional may sustain an additional injury due to compression, rendering the situation irretrievable. Invariably a judgment is made based on the condition of the infant before onset of symptom progression and the degree of disability at the time of decision making.

Older children and adolescents have a more insidious presentation, with headache and lower cranial nerve dysfunction (weakness in gag, tongue, voice and swallowing) predominating early with fainting episodes and abnormal eye movement following. If hydromyelia develops, there will be increasing spasticity in the arms and legs as well as progressive weakness and changes in sensation. Once again the first question to be answered is whether there is a shunt malfunction. If there is not, then attention is directed toward whether the severity of symptoms mandates a surgical decompression of the malformation.