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. The malformation was also reported some years later by Julius Arnold, a professor of pathology at the University of Heidelberg.² His students used the term Arnoldsche und Chiarische Missbildung and we now call it the Arnold-Chiari malformation.³ 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.⁴
• Some authors have added a severe form of cerebellar hypoplasia without displacement of brain through the foramen magnum and called it Chiari IV malformation.
• A case of acquired Chiari malformation secondary to skull hyperostosis has been described.⁵

Epidemiology

Chiari type I⁶

The true incidence is not known. It was originally considered a rare condition but the advent of the MRI scan suggests it is commoner than was once thought. One study reported a rate 0.6% in all age groups and a rate of 0.9% was reported in a study of only paediatric patients.⁶ There is a female preponderance of around 3:2. There tends to be a familial aggregation suggesting a genetic component.⁷ 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.⁶

Chiari type II (Arnold-Chiari malformation)

An American study found a frequency of 1 in 1,000 in the United States. Of 69 autopsies performed on hydrocephalic patients, 31 demonstrated a Chiari II malformation.⁸

Presentation

Chiari type I^6,9

The presentation of this condition depends upon the severity of the herniation and associated other features. The hydrodynamics of the cerebrospinal fluid (CSF) are upset, possibly causing caudal to cranial flow and this is a contributor to symptoms.⁷ A variety of symptoms can occur:

• Suboccipital headaches are common.
• Pain behind the eyes, visual disturbances, diplopia and photophobia can occur.
• Bilateral hearing loss has been reported.¹⁰
• 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^8,11

• 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 upper motor neurone (UMN) features
• Recurrent pneumonia from aspiration
• Gradual loss of function

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

Investigations^6,8,12

• The investigation of choice is MRI as it shows excessive CSF or loss of neural tissue so well; however, 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 CSF flow.¹³
• Plain X-ray of the skull and cervical spine will show skeletal abnormalities like scoliosis.
• CT scan demonstrates caudal displacement of the fourth ventricle.
• Ultrasound scan is only useful whilst the fontanelle is open and it tends not to offer information that other techniques do not.
• It is, however, useful for prenatal screening in Chiari type I and II.^14,15

Management

Non-surgical

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

Surgical

Chiari type I⁶
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 usually 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.¹⁶
• A shunt is usually inserted in the presence of a large syrinx with or without hydrocephalus.¹⁷ However, endoscopic third ventriculostomy provides a suitable alternative. It may be effective as a primary treatment. Management of hydrocephalus alone is often sufficient and may obviate decompression, although a significant proportion of patients will still need both procedures.¹⁸
• 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.^12,13
• Chiari-related syringomyelia can be treated successfully with surgery.¹⁹

Prognosis

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.²¹ Adult patients with associated scoliosis and syringomyelia are more likely to develop complications and have a poorer response to surgical treatment.²² A few patients resolve spontaneously.⁶

Chiari type II

The under 2 age group is at greatest risk of fatalities and complications, mainly resulting from hindbrain herniation.⁸ 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.²³

Document references

1. Hans Chiari; whonamedit.com
2. Julius Arnold; whonamedit.com
3. Chiari Malformation Information Page; National Institute of Neurological Disorders and Stroke 2009
4. Garg K, Malik N, Jaiswal, A et al; Chiari III malformation with hypertelorism and microcephaly in a neonate: Case report and a review of the literature. J Pediatr Neurosci 2008;3:169-71
5. Albert L Jr, Hirschfeld A; Acquired Chiari malformation secondary to hyperostosis of the skull: a case report and literature review. Surg Neurol. 2009 Aug;72(2):157-61. Epub 2008 Jun 2. [abstract]
6. Siddiqi, N Laine,F; Chiari I Malformation eMedicine, 2009.
7. Milhorat TH, Chou MW, Trinidad EM, et al; Chiari I malformation redefined: clinical and radiographic findings for 364 symptomatic patients. Neurosurgery. 1999 May;44(5):1005-17. [abstract]
8. Incesu, L Khosla A; Chiari II Malformation eMedicine, 2008.
9. Chiari Malformation Type 1; OMIM 2007
10. Dolgun H, Turkoglu E, Kertmen H, et al; Chiari Type I malformation presenting with bilateral hearing loss. J Clin Neurosci. 2009 Sep;16(9):1228-30. Epub 2009 Jun 4. [abstract]
11. Chiari Malformation Type II; OMIM 2007
12. Sridharan, S Krishnaney, A; Management of Chiari Malformation and Fibromyalgia spineuniverse.com 2007
13. McGirt MJ, Nimjee SM, Fuchs HE, et al; Relationship of cine phase-contrast magnetic resonance imaging with outcome after decompression for Chiari I malformations. Neurosurgery. 2006 Jul;59(1):140-6; discussion 140-6. [abstract]
14. Iruretagoyena JI, Trampe B, Shah D; Prenatal diagnosis of Chiari malformation with syringomyelia in the second trimester. J Matern Fetal Neonatal Med. 2009 Jul 1:1-3. [abstract]
15. Callen AL, Stengel JW, Filly RA; Supratentorial abnormalities in the Chiari II malformation, II: tectal morphologic changes. J Ultrasound Med. 2009 Jan;28(1):29-35. [abstract]
16. Ergun R, Akdemir G, Gezici AR, et al; Surgical management of syringomyelia-Chiari complex. Eur Spine J. 2000 Dec;9(6):553-7. [abstract]
17. Alzate JC, Kothbauer KF, Jallo GI, et al; Treatment of Chiari I malformation in patients with and without syringomyelia: a consecutive series of 66 cases. Neurosurg Focus. 2001 Jul 15;11(1):E3. [abstract]
18. Hayhurst C, Osman-Farah J, Das K, et al; Initial management of hydrocephalus associated with Chiari malformation Type I-syringomyelia complex via endoscopic third ventriculostomy: an outcome analysis. J Neurosurg. 2008 Jun;108(6):1211-4. [abstract]
19. Aghakhani N, Parker F, David P, et al; Long-term follow-up of Chiari-related syringomyelia in adults: analysis of 157 surgically treated cases. Neurosurgery. 2009 Feb;64(2):308-15; discussion 315. [abstract]
20. Stevenson KL; Chiari Type II malformation: past, present, and future. Neurosurg Focus. 2004 Feb 15;16(2):E5. [abstract]
21. Strayer A; Chiari I malformation: clinical presentation and management. J Neurosci Nurs. 2001 Apr;33(2):90-6, 104. [abstract]
22. Ono A, Ueyama K, Okada A, et al; Adult scoliosis in syringomyelia associated with Chiari I malformation. Spine. 2002 Jan 15;27(2):E23-8. [abstract]
23. Rintoul NE, Sutton LN, Hubbard AM, et al; A new look at myelomeningoceles: functional level, vertebral level, shunting, and the implications for fetal intervention. Pediatrics. 2002 Mar;109(3):409-13. [abstract]

Internet and further reading

• Information about Syringomyelia and Arnold Chiari Malformation; Ann Conroy Trust 2007
• Aitken LA, Lindan CE, Sidney S, et al; Chiari type I malformation in a pediatric population. Pediatr Neurol. 2009 Jun;40(6):449-54. [abstract]
• Isik N, Elmaci I, Silav G, et al; Chiari malformation type III and results of surgery: a clinical study: report of eight surgically treated cases and review of the literature. Pediatr Neurosurg. 2009;45(1):19-28. Epub 2009 Feb 17. [abstract]

Acknowledgements