Arnold-Chiari Malformation

Hans Chiari was a German pathologist who, between 1891 and 1896, described various anomalies of the caudal cerebellum and brainstem from post mortem studies.¹

• He first described an abnormality of elongated peg like cerebellar tonsils that are displaced into the upper cervical canal through the foramen magnum. This is now called the Chiari Type I malformation. Abnormalities of the skull and upper vertebrae are common in this type.
• Five years later he reported a complex congenital malformation of the brain, nearly always associated with myelomeningocele. It is now called the Chiari Type II malformation. This condition includes downward displacement of the medulla, fourth ventricle, and cerebellum into the cervical spinal canal, as well as elongation of the pons and fourth ventricle, probably due to a relatively small posterior fossa. About 25% have distension of the central or paracentral canal of the cervical spinal cord, causing hydromyelia or syringomyelia.
• He also described a single case of cervical spina bifida with herniation of the cerebellum through the foramen magnum, now called Chiari III malformation.
• Some authors have added a severe form of cerebellar hypoplasia without displacement of brain through the foramen magnum and called it Chiari IV malformation.

Julius Arnold was professor of pathology at the University of Heidelberg.² He did not work with Chiari and his descriptions were a few years later but his students used the term Arnoldsche und Chiarische Missbildung and we now call it the Arnold-Chiari malformation.

Chiari Type I³

The true incidence is not known. It was originally considered a rare condition but the advent of MRI scan suggests it is commoner than was once thought. There is a female preponderance of around 3:2. There tends to be a familial aggregation suggesting a genetic component.⁴ The age at presentation can vary from 6 to 60 years with a mean around 40 years. It tends to present earlier if there is syringomyelia.³

Chiari Type II

An American study found a frequency of 1 in 1000 in the United States. Of 69 autopsies performed on hydrocephalic patients, 31 demonstrated a Chiari II malformation.⁵

Chiari Type I^3,6

The presentation of this condition depends upon the severity of the herniation and associated other features. The hydrodynamics of the CSF are upset, possibly causing caudal to cranial flow, and this is a contributor to symptoms.⁴ A variety of symptoms can occur:

• Suboccipital headaches are common.
• Pain behind the eyes, visual disturbances, diplopia and photophobia can occur.
• Dizziness, vertigo, disturbance of hearing and nystagmus may develop.
• Compression of the hindbrain can cause weakness, paraesthesia, ataxia, cranial nerve palsies, dysphagia, dysphasia, palpitations, syncope, apnoea, and sudden death.
• Problems of the spinal cord present in about 95% of patients with syringomyelia and two thirds of those without it. Symptoms include central cord syndrome, impaired sensation, impaired motor control, gait disturbance, torticollis, bowel and/or bladder symptoms, neuropathic joints, trophic phenomena, and pain.
• Various abnormalities of the skull and upper vertebrae are found in 25 to 50%.

Chiari Type II^5,7

• This tends to present much earlier with significant morbidity and mortality in the neonatal period.
• A third of patients with meningomyelocoele develop brainstem dysfunction by the age of 5 and a third of these die in infancy.
• Cranial nerve and brainstem dysfunction are the most serious features.
• There are 2 types of presentation in Type II. One involves infants and the other older children. Infants rarely present before a few weeks old but life is threatened by involvement of cranial nerves IX and X and compression of the respiratory centre.

• Inspiratory stridor
• Dysphagia or nasal regurgitation
• Aspiration from bilateral abductor vocal cord paralysis or central neural dysfunction or both
• Respiratory distress
• Episodes of apnoea
• Weak cry
• Scoliosis
• Quadriparesis
• Opisthotonic posture

• Syncope
• Nystagmus
• Spastic quadriparesis with UMN features
• Recurrent pneumonia from aspiration
• Gradual loss of function

Presentation of Types III and IV have been ignored as they are much rarer.

• The investigation of choice is MRI as it shows excessive CSF or loss of neural tissue so well but it may be less effective at demonstrating lesions of bone. MRI now means that myelography is not required. Injection of a contrast and enhancing agent such as gadolinium may help to clarify the anatomical abnormalities. The use of cine MRI is sometimes necessary to elucidate whether an abnormality seen on static films is causing a significant physiological obstruction to cerebrospinal fluid (CSF) flow.⁹
• Plain X-ray of the skull and cervical spine will show skeletal abnormalities like scoliosis.
• CT demonstrates caudal displacement of the fourth ventricle.
• Ultrasound is only useful whilst the fontanelle is open and it tends not to offer information that other techniques do not.

Non-Surgical

All patients, whether they are suitable for surgery or not, should be considered for rehabilitative therapy and psychological support.

Surgical

Chiari Type I

The main issues to be determined in the management of a patient with a Chiari I malformation are:

• What is the anatomical malformation?
• What are the main disabling symptoms?
• How does the malformation relate to physical symptoms?

A decision on whether to proceed to surgery should be based on the following approach:

• A multidisciplinary assessment is helpful, with neurologists, neurosurgeons and rheumatologists all giving an opinion about the patient.
• A decision regarding surgery should be taken on reviewing these opinions together with the imaging results.
• Suboccipital craniectomy and upper cervical laminectomy to decompress the malformation at the foramen magnum is required with cord drainage and institution of drainage of the fourth ventricle, if necessary.
• Decompression of the foramen magnum gives good results in terms of arresting deterioration.¹⁰
• The issue of whether or not to insert a shunt in the presence of a large syrinx is currently under review.¹¹
• Patients most likely to benefit from surgery are those with reproducible neurological signs (e.g. nystagmus, absent gag reflex), and demonstrably abnormal CSF flow in the hindbrain on cine MRI.^8,9

Chiari Type I

Some patients are asymptomatic and remain so for the length of their lives. Many however develop serious neurological sequelae, and these are probably the patients with the greatest degree of tonsillar herniation. Generally speaking, the prognosis of patients who undergo surgical treatment is variable and depends on the symptomatology at the time of presentation and the recovery potential of the spinal cord.¹³ Adult patients with associated scoliosis and syringomyelia are more likely to develop complications and have a poorer response to surgical treatment.¹⁴ A few patients resolve spontaneously.³

Chiari Type II

The under 2 age group is at greatest risk of fatalities and complications, mainly resulting from hindbrain herniation.⁵ A review of the literature shows a steady improvement in mortality and morbidity figures, as diagnostic and surgical techniques improve. One study of 297 patients with myelomeningocoele (the principle abnormality in Chiari Type II) showed a mortality rate of 2%, which is significantly lower than previous studies.¹⁵