Chiari Malformation (CM)

A Chiari Malformation is a congenital bony deformity of the rear underside of the skull and the first cervical vertebra.
The malformation causes the lowest part of the cerebellum (the cerebellar tonsils) and / or the brainstem to droop towards the spinal cord, due to an opening in the base of the skull.
In normal circumstances, the cerebellum and brain stem are located in the cranial cavity, above the opening in the occipital bone of the skull (the foramen magnum).


It does not always have to be a congenital defect. If, due to a brain disorder, the the brain takes up more space, parts of the cerebellum and brainstem may also move down and outside the skull. This is often referred to as a cerebellomedullary malformation.


Complaints that may occur depend on the severity of the situation. Sometimes there are no complaints, sometimes there are serious complaints with disturbed brain functions, and sometimes complaints only come to light later in life in case the condition
is congenital, but has not been noticed.


Four types

  • Type I

In a Chiari malformation type I, the skull that was probably too small during its development, leaving no room for part of the cerebellum within the skull.
Often there are also other bone abnormalities, such as cervical vertebrae that are (partly) attached to each other or to the skull, or have an open arch.

In case of type I, the lowest part of the cerebellum, the cerebellar tonsils, have sunk at least 4 mm into the spinal canal. This does not always have to cause complaints. That is why this condition is sometimes only discovered by chance.


  • Type II

In a Chiari type II, in addition to the cerebellar tonsils, other areas of the cerebellum, brainstem and fourth brain cavity has sunk into the spinal canal.

Because there is no space, the brain stem is also narrower than usual. Type II often occurs together with hydrocephalus and  meningomyelocele. A meningomyelocele usually results in partial or complete paralysis of the area below the spinal cord opening. The higher in the back, and therefore closer to the head, the opening is, the greater the consequences may be.


  • Type III

This is a rarer condition in which part of the membranes surrounding the brain or spinal cord, brain, brainstem and spinal cord end up in a kind of sac (encephalocele), outside the skull.
There may be other brain abnormalities. The posterior part of the skull and / or the vertebral arches may be open.
Type III causes serious complaints. Many type II symptoms are similar to type II symptoms. However, more serious neurological disorders also occur, including epilepsy and developmental problems..


  • Type IV

Type IV is also a very rare abnormality with very serious complaints.

A child with this defect is not viable. The small
brain is incomplete, underdeveloped or not constructed (cerebellar hypoplasia), nor is the back part of the skull
constructed. Parts of the skull and spinal cord may be visible.


Cause of complaints

The complaints are related to the degree of pressure or oppression of the brain, membranes, spinal cord, nerves or bone that is involved. They are also related to the brain area involved: brainstem or cerebellum.
The complaints are also related to the build-up of high pressure  of cerebrospinal fluid (CFS).


Possible complaints

  • Headache, usually at the back of the head, especially with coughing, sneezing, straining and exertion (suboccipital headache)
  • Pain in the neck
  • Blurred or poor vision or light sensitivity
  • Eyeball jerks (nystagmus)
  • Oscillopsia, where the image moves when the head is moved, which can cause problems with balance
  • Problems maintaining balance, balance disorders, balance problems, coordination problems (ataxia),
  • Dizziness
  • Sensory changes in arms or legs, tingling, pricking sensations, numbness
  • No longer feeling the difference between temperature differences of hot or cold (sensitivity disorder)
  • Breathing problems, rapid breathing, wheezing, pauses in breathing (apnea) or sleep apnea (both obstructive and central sleep apnea can occur)
  • Respiratory tract infections
  • Difficulty swallowing or difficulty removing saliva, choking, gagging
  • Difficulty speaking
  • Hoarseness (dysphonia) or changes in the voice
  • Nausea, vomiting
  • Fecal/urinary incontinence
  • Difficulty speaking, difficulty articulating (dysarthria), difficulty speaking consciously (apraxia of speech)
  • Ringing in the ears (tinnitus)
  • Abnormal lateral twisting and curvature of the spine (scoliosis)
  • Hydrocephalus, because the daily amount of brain fluid produced has difficulty finding its way to the spinal cord. The cerebral cavities become overfilled with this cerebrospinal fluid
  • Dilated cavity in the spinal cord (syringomyelia). The cavity is dilated by the amount of cerebrospinal fluid that has no other route. Usually the cavity is at the level of the cervical vertebrae


Other possible complaints

  • Insomnia
  • Depression
  • Overweight, underweight
  • Changes to the cervical vertebrae



The most common procedure is surgery to create more space for the small brain (cerebellum). In addition, the pressure on the spinal cord is reduced and the normal flow of the spinal fluid is restored.

The surgery is called posterior fossa decompression.

Sometimes the bony roof of the spinal canal (vertebral arch or lamina) is removed (spinal laminectomy).


A shunt can be applied in the case of hydrocephalus or hydrocephalus. This can drain excess fluid and relieve pressure in the head. The fluid is either drained to the abdominal or chest cavity. There it is absorbed by the body. If a shunt becomes clogged, the surgeon can replace the part that has become clogged or replace the entire shunt.


More information:



NHS (UK): Spina Bifida