Chiari Malformations

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Chiari malformations\: Abnormal displacement of the hindbrain (cerebellum, medulla oblongata, pons) into the spinal canal
through a skull defect. Occurs in 1 in 1000 births, with a slight female predominance (3\:1 ratio).
Type 1\: Most common and mildest form; presents in late childhood or adulthood; downward displacement of cerebellar
tonsils >5mm through foramen magnum.
Type 2\: Also known as Arnold-Chiari malformation; involves more brain tissue and a shallower posterior fossa; associated
with myelomeningocele; presents in early childhood or infancy.
Type 3\: Rare, involves herniation of posterior fossa contents through a posterior encephalocele; poor prognosis.
Type 4\: Very rare, not compatible with life; involves incomplete development of the cerebellum.
Symptoms\: Sub-occipital headaches (worsened by Valsalva manoeuvres), Lhermitte’s sign, neck pain, dizziness, balance
problems, limb weakness, numbness/tingling, double vision, slurred speech, swallowing problems, hearing loss, tinnitus.
Clinical
nystagmus).
Investigations\: MRI head and spine (high-resolution images of skull defect and neural structures), ultrasound (prenatal
screening).
Management\:
Conservative\: Monitoring for asymptomatic patients.
Surgical\: For symptomatic patients; options include posterior decompression of the foramen magnum, ventriculoperitoneal
(VP) shunt, and syringo shunt.
Complications\: Hydrocephalus (blockage of normal CSF drainage), syringomyelia (formation of a CSF-
the spinal cord).
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Introduction

Chiari malformations are a group of conditions characterised by abnormal displacement of the hindbrain (cerebellum,
medulla oblongata, pons) into the spinal canal through a defect in the skull.
1
Chiari malformations are estimated to occur in 1 in 1000 births and with a slight female predominance (3\:1 ratio of females
to males).

Aetiology

There are four types of Chiari malformations.
2
Type 1 Chiari malformation
Type 1 Chiari malformation is the most common and mildest form of the disease.
Patients with type 1 malformations tend to present during late childhood or adulthood.Type 1 Chiari malformation is characterised by a downward displacement of the cerebellar tonsils, of more than 5mm,
through the foramen magnum.
This type of malformation can occur due to congenital or acquired (e.g. previous neurosurgery) structural defects in the
skull base.
The defect in the skull base reduces the space available in the posterior fossa for the cerebellum, resulting in the
cerebellar tonsils protruding through the foramen magnum. As a result, nearby neurological structures can become
compressed, which then causes neurological symptoms and signs.
Type 2 Chiari malformation
Type 2 Chiari malformation (also known as Arnold-Chiari malformation) involves a greater range of brain tissue and a more
shallow posterior fossa than is seen in type 1.
There is downward displacement of the cerebellar tonsils, as well as the fourth ventricle, brainstem and inferior vermis.
Because there is more brain matter involved with this type of malformation, the clinical presentation tends to be more
severe than type 1.
People with this type of malformation present earlier, typically during early childhood or even infancy.
Type 2 Chiari malformation is also often associated with myelomeningocele as a result of the vertebrae and spinal canal
not closing properly before birth (i.e. spina bi
Type 3 Chiari malformation
Type 3 Chiari malformation is much rarer than type 1 and 2. In type 3, there is herniation of the posterior fossa's contents
through a posterior encephalocele.
This is a rare congenital type of neural tube defect in which a portion of the skull has not formed properly, which enables
parts of the brain and meninges to protrude through it. It is usually associated with a poor prognosis.
Type 4 Chiari malformation
Type 4 Chiari malformation is very rare and is not compatible with life. It involves the incomplete development of
the cerebellum.

Clinical features

This section will focus on the clinical features of type 1 and type 2 Chiari malformations.
Although both type 1 and type 2 Chiari malformations present with similar clinical features, the severity of these features is
typically worse in patients with a type 2 malformation.
History
Typical symptoms of type 1 and 2 Chiari malformations include\:
1-3
Sub-occipital headaches\: often worsened by Valsalva manoeuvres such as coughing, straining or sneezing
Lhermitte’s sign\: an electric shock-type sensation that, upon neck
the limbs
Neck pain
Dizziness and balance problems
Arm and/or leg weakness
Numbness/tingling in the arms and/or legs
Double vision
Slurred speech
Swallowing problems
Hearing loss
Tinnitus
Clinical examinationAll patients require a thorough neurological examination.
Typical clinical
1-3
Motor or sensory de
Dysarthria
Diplopia
Sensorineural hearing loss
Cerebellar features such as ataxia and nystagmus

Investigations

Imaging
Relevant imaging investigations include\:
MRI head and spine\: can provide high-resolution images of the defect in the skull and the position of the neural
structures in the cranium and spinal canal
Ultrasound\: used for prenatal screening and can identify Chiari malformations in utero
Figure 1. Type 1 Chiari malformation, shown in red, on an MRI scan.
5

Management

Conservative management
A conservative approach is adopted for patients who remain asymptomatic despite their Chiari malformation.
Routine monitoring of the defect and associated structures may be performed to allow early identi
complications.
Surgical management
Surgical management is o
of associated complications.Patients with symptomatic type 2 Chiari malformations are typically o
signi
Surgical treatments aim to decompress the brainstem and relieve pressure within the skull and spinal canal.
The main surgical options for the management of Chiari malformations include\:
Posterior decompression of the foramen magnum
Ventriculoperitoneal (VP) shunt\: to treat secondary hydrocephalus
Syringo shunt (to treat some forms of syringomyelia - e.g. syringo-subarachnoid shunt)

Complications

Complications of Chiari malformations may include\:
Hydrocephalus\: due to the blockage of normal CSF drainage within the CSF
Syringomyelia\: a CSF-
syrinx destroys the centre of the spinal cord, resulting in pain, weakness and sensory loss.

References

National Institute of Neurological Disorders and Stroke. C h i a r i M a l f o r m a t i o n F a c t S h e e t . Published in 2018. Available from\:
[LINK]
Jones J. C h i a r i m a l f o r m a t i o n s . Published in 2018. Available here\: [LINK]
Khare S, Seth D. A n n a l o f I n d i a n A c a d e m y o f N e u r o l o g y . 2015. April; 18(2)\: 154-156. DOI\: 10.4103/0972-2327.150622 Available
from\: [LINK].
Neurosurgery Department at Great Ormond Street Hospital for Children. E n c e p h a l o c e l e . Available from\: [LINK].
Frank Gaillard (Radiopaedia 2592). Chiari Malformation 1. License\: [CC-BY-NC-SA]
Frank Gaillard (Radiopaedia 16048). Chiari Malformation 2. License\: [CC-BY-NC-SA]

Reviewer

Mr Konstantinos Lilimpakis
Neurosurgical Clinical Fellow

Aphasia
Benign Paroxysmal Positional Vertigo (BPPV)
Cervical Radiculopathy
Down's Syndrome
Epilepsy

Test yourselfContents

Introduction
Aetiology
Clinical features
Investigations
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