Chiari malformation refers to a condition where part of the cerebellum is positioned within the foramen magnum. There are four types, Chiari II and Chiari II (also sometimes referred to as Arnold-Chiari malformation) and Chiari III & IV – these last tow types are very rare.
Chiari type I
- The cerebellar tonsils are displaced into the upper cervical canal
- The tonsils themselves are often elongated and sometimes referred to as ‘peg-like’
- There may be associated abnormalities of the skull and cervical vertebrae
- Clinically tends to have the mildest symptoms – many cases are asymptomatic
- Incidence of about 1 in 2000
Chiari type II
- Displacement of the medulla, 4th ventricle and cerebellum into the spinal column
- Usually associated with myelomeningocoele – which is a congenital defect whereby part of the spinal cord develops outside of the body, contained within a fluid-filled sac, and is seen in certain severe cases of spina bifida
Chiari type III
- Similar to type II Chiari malformation – this is a variation of spina bifida that involves herniation of the cerebellum into the spinal column
The condition is named after Hans Chiari – a German pathologist who described various neurological abnormalities in the 1890s.
Presentation can vary widely depending on the degree of herniation. Cases of type I Chiari malformation may be asymptomatic. The degree of symptoms is often dependent on the flow of CSF – in more symptomatic cases there is more likely to be disruption of the flow of CSF and it may even flow in a caudal to cranial direction.
Type I Chiari Malformation
Presentation can occur at any stage of life. More severe cases tend to present earlier.
- Headaches – usually occipital and neck regions
- Periorbital pain is also common
- Visual distrubance
- Dizziness, vertigo, nystagmus
- Cerebellar signs
- Spinal cord related signs
- Altered sensation
- Altered motor function
- Bladder or bowel symptoms
- Other neurological signs
- Cranial nerve palsy
- Skull and vertebrae abnormalities in up to 50% of cases
Type II Chiari Malformation
Typically presents at a young age (sometimes as early as the neonatal period). Assocaited with significant mortality and morbidity. There are typically two types of presentation – those in infants and those in adolescents.
- Only seen in individuals with meningomyelocele – which is seen in more severe cases of spina bifida
- Occurs in 30% of cases of meningomyelocele
- Mortality at age of 5 years is about 30%
- Associated with significant cranial nerve and brainstem dysfunction
- Nasal regurgitation
- Apnoeic episodes
- Weak cry
- Symptoms often progressive
- Quadriparesis – typically with UMN signs
- Recurrent episodes of aspiration and aspiration pneumonia
- The gold standard investigation
- With contrast may provide better quality images for diagnosis of Chiari malformation
- Cine MRI may help to determine CSF flow
- Of the skull and spinal cord can show structural deformities
- Less useful than MRI
- May show ventricular abnormalities of the 4th ventricle
- Can be used in neonates with an open fontanelle
- Used mainly as a screening tool where appropriate
All patient should be offered rehabilitation therapy. Surgery is indicated in many cases.
Patients with obvious reproducible neurological sings – such as nystagmus, or specific weakness are most likely to benefit from surgery.
- MDT approach to determine the indication for surgery
- In particular – a close assessment of the symptoms in relation to the visualised structural abnormalities should be made
- Typical surgical therapies might include craniectomy and/or upper cervical laminectomy to decompress the malformation.
- This is often effective at preventing further deterioration but may not improve ongoing symptoms
- A shunt may also be used, even without the presence of hydrocephalus
- There are some case reports of spontaneous resolution of Chiari I
- Many cases are asymptomatic and do not require intervention
- Earlier surgery is associated with better long-term outcome