Presentation

Anomalies of the base of the skull and spine are seen in 30-50% of patients with the Chiari Malformation, Type 1. These anomalies include:

• basilar impression (compression of the upper part of the spine into the base of the skull with resultant compression of the brainstem)
• 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 (16-80% 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%). 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)
  

There have been reported cases of children with previously undiagnosed Chiari Malformations sustaining injuries to the spinal cord with no obvious abnormality in the x-rays of their spine. The evaluation of children who have sustained a spinal cord injury should include a MR scan of their spinal cord which includes imaging of the base of the brain to rule out a Chiari Malformation.

Chiari ll Malformation

As stated previously, this malformation is part of a larger syndrome seen in children with myelodysplasia (spina bifida). This is frequently misunderstood and I receive frequent emails from individuals thinking they have 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% will exhibit symptoms which warrant treatment. Those destine to exhibit symptoms will do so either early in infancy or later in childhood with the presentation and outlook differing for the two groups.

Those infants destine to develop difficulties due to their Chiari Malformation will do so after several weeks or months of relative normalcy. Their families will notice increasingly stridorsis breathing, a 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 rapidly progress from this point.

Treatment of infants with this condition is controversial. The first question to be answered is the shunt malfunctioning for if it is, these symptoms can rapidly be reversed with correction of the shunt's functioning. On the other hand, if the symptoms are due to the Chiari Malformation, treatment becomes more difficult and controversial. This is because it is particularly difficult in infants to differentiate symptoms due to mechanical compression of the lower brain stem from symptoms due to a untreatable malformation of the lower brain stem. Additionally, there can be a combination of the two processes when an abnormally formed brainstem which is marginally functional sustains an additional injury due to compression rendering the situation unretrivable. Invariably a judgment is made based on the condition of the baby 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 "is there a shunt malfunction?" If there is not then attention is directed towards whether the severity of symptoms mandate a surgical decompression of the malformation.

Peter Semczuk,