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Chiari Malformation & EDS

Posted By Alan Hakim, April 15, 2014

This article is written for both patients with Ehlers-Danlos Syndrome (EDS), healthcare professionals, and the general public. It describes the nature of type 1 Chiari malformation, the symptoms that can be associated with it, what we currently understand about the association with EDS, how it is identified, and the treatment options. This article does not discuss cranio-cervical or cervical instability.

What is a Chiari malformation?

In some people the lower part of the brain can sit much lower than normal so that it is below the entrance to the skull. This is called a Chiari malformation (CM). It may cause no problem at all, however in this position it can put pressure on the lowest part of the brain and the top of the spinal cord and cause symptoms.

There are 3 types of CM.  Type 1 CM is the most common and the least serious form of the condition. In type 1 CM the lowest part of the back of the brain called the cerebellar tonsils is found to lie at the top of the spinal canal rather than the normal position inside the base of the skull. There may also be tethering of the spinal cord. Here the cord has become abnormally attached within the spine and is less free to move with movement of the spine. There occasionally may also be a syrinx – a fluid filled cavity in the spinal cord or brain stem.

Type 2 and 3 CM are less common. They are more serious. They are associated with a condition called spina bifida, a birth defect of spine development, and a condition called hydrocephalus that describes a build-up of fluid in the brain.

This article focuses on type 1 CM. To read more about CM in general take a look at the NHS page by clicking HERE, or the National Institutes of Health page HERE.

What are the symptoms?

Many people with a type 1 CM will not have any symptoms, or do not develop symptoms until later in life.

The symptoms include:

  • headaches, usually at the back of the head – these are brought on, or made worse by, exercise, straining, laughing or bending over
  • neck pain
  • dizziness and balance problems
  • numbness or tingling in the arms or legs
  • blurred vision and involuntary movement of the eyes (nystagmus)
  • swallowing problems
  • hearing loss and ringing in the ears (tinnitus)
  • feeling sick and vomiting

The difficulty with many of theses symptoms is that they might also come from a combination other musculoskeletal problems, migraine, cardiovascular autonomic problems (e.g. POTS and hypotension (read more)), and gastric problems (read more). A detailed assessment by a doctor is required to determine how all the symptoms might fit together.

How common is Type 1 CM in the General Population?

The National Institute for Neurological Disorders and National Institutes of Health state that type 1 CM is said to occur in about 1 in 1000 people. However they recognize that the overall frequency is difficult to know given that CM is often asymptomatic and found incidentally in people having CT or MRI scans for another reason.

Is Type 1 CM more common in neck pain suffers than in the General Population?

We do not know the answer to this question.

In 2010 Freeman and colleagues published a paper describing the study of 1200 individuals with neck pain (Reference 1). Half of them were people with neck pain symptoms but with no recent history of trauma; the other half was made up of people with neck symptoms caused by vehicle-related accidents (whiplash). Everyone had an MRI. The researchers found that in the first group (the non-trauma control group) around 5% of people had a type 1 CM. In the second group (the symptomatic trauma group) the researchers found that around 10-20% had a type 1 CM. This study suggests that around 1 in 10 people with neck pain might be shown to have a CM, though how this affects their symptoms and recovery is not clear.

So, is CM more common in neck pain suffers than non-neck pain suffers?

To try and find the answer to this question one would have to scan a large general population that included people with and without neck pain to see if there was any difference between them.

Is CM more common in people with EDS than in the general population?

Again, we do not know the answer to this question. To attempt to answer this question one would have to study a large number of patients with EDS and compare them with a population that did not have EDS.

However, there is some evidence to suggest that the cause of a CM in EDS may be different. There is one published large study that has looked at the association between type 1 CM and EDS. This was undertaken by Milhorat and colleagues at The Chiari Institute, New York, USA (Reference 2). They looked at 2813 patients with a known diagnosis of type 1 CM. They found that 357 (12-13%) had features of EDS.

The researching team noted that the mechanisms that may cause EDS to become symptomatic in the presence of CM could be:

i. Sliding of tissues down from their normal resting position when in the upright position, and or

ii.. Hypermobility at in the vertebral bones at the very top of the neck, leading to changes in the position / angle of these bones when upright.

This is a helpful insight in to the type of imaging that should be considered when assessing EDS patients (see below).

Is spinal cord tethering linked to EDS and CM?

In a separate study by Milhorat’s team an association was found between tethering of the spinal cord and type 1 CM (Reference 3). Tethering arose in 14% of 408 patients studied. However, it is important to note that they did not look at how often this specifically occurred in EDS cases. Also, the anatomical findings that they note as being particularly common to the tethered cord in type 1 CM were not the same as the findings recorded in their study looking at EDS patients. It should be considered for now that it is not known whether there is an association between EDS and spinal cord tethering in type 1 CM.

How is CM diagnosed?

This requires Magnetic Resonance Imaging (MRI) of the brain and the first part of the spinal cord. It is stated that this should be in the ‘upright position’, however there is no absolute evidence for this, although there is logic in this for EDS patients based on observing the effect of gravity on lax tissues as per the observations made in Milhorat’s study (Reference 2).

It should be noted however that upright MRI facilities are difficult to access at present in the UK as there are very few machines. Also, it cannot be assumed that funding would automatically be made available through the NHS. It is very likely doctors would need to seek approval for funding from local Commissioners (read more).

In Freeman’s study (Reference 1) half of each group had normal recumbent (laying) MRI and half had upright MRI. In the non-trauma group the frequency (prevalence) of CM was the same regardless of the type of scan. In the trauma group, upright MRI picked up twice as many cases compared to recumbent MRI but one must note that approximately 80-90% of all people in the study had no abnormality at all on MRI.

A pragmatic approach would seem to be that where there is a clinical concern, and after detailed clinical assessment, a recumbent MRI should be performed first. If a CM is not found by this method then an upright MRI should be considered. If surgery was being considered further tests to look at stability of the neck are likely to also be required.

How is a CM treated?

A type 1 CM is usually managed with medication to try and relieve the various symptoms.

In general if surgery is performed then a decompression procedure is undertaken. Here the surgeon makes an incision at the back of the head and removes a small piece of bone from the base of the skull. This will widen the space in the opening to the skull. A small piece of bone from the top of the spine is also removed. The aim is to increase the space around the spinal cord and relieve the pressure of the brain pressing on the cord.

However, one must think very carefully about this in EDS, not just because of the potential increased risk of bleeding, poor wound healing, and scarring. If laxity of the brain supporting tissues is leading to the brain pressing down on the cord then there is a theoretical and unknown risk that these lax tissues will simply drop further in to the enlarged space made by the surgery. Also, if there is instability of the upper neck then this should probably be surgically treated. These are very complex issues for which require expert neurosurgical advice.

As with all types of surgery there are potential complications, and surgery may result in no improvement or worsening of symptoms. In the type of surgery undertaken for CM these risks include:

  • stroke or bleeding
  • paralysis of the limbs
  • meningitis or other infection
  • impaired speech
  • memory loss or problems with thinking
  • swallowing impairment
  • balance problems
  • fits or seizures, and
  • a risk to life


The ‘bottom line’ is:

i. There is a probable association between Chiari Malformation and Ehlers-Danlos syndrome

ii. There is no known association between Chiari Malformation and hypermobility per se.

iii. Some individuals with a Chiari malformation may also have a syrinx.

iv. There is no known direct association between syrinx and either hypermobility or Ehlers-Danlos syndrome.


Like so many aspects of Medicine this area is complex. A detailed medical assessment is required before determining whether MRI tests might help in making a diagnosis.

Non-surgical treatments including medicines to manage symptoms and physical therapies to strengthen and stabilize the neck should be tried first.

Surgery can be effective but it is difficult to determine whether it is appropriate in many cases, and there are significant risks. This should always be thought through carefully with expert advice

For a review of what we know of Cranio-Cervical instability in hEDS and the role of dynamic MRI please read the open access paper Reference 4 below.


Dr A J Hakim MA FRCP, Chief Medical Advisor and Trustee

Published April 2014, Reviewed by Prof R Grahame, Dr H Cohen, and Donna Wicks. Revised Nov 2017. Planned update Summer 2018.


1. Freeman MD, Rosa S, Harshfield D, et al. A case-control study of cerebellar tonsillar ectopia (Chiari) and head/neck trauma (whiplash). Brain Inj. 2010;24(7-8):988-94.

2. Milhorat TH, Bolognese PA, Nishikawa M, McDonnell NB, Francomano CA. Syndrome of occipitoatlantoaxial hypermobility, cranial settling, and chiari malformation type 1 in patients with hereditary disorders of connective tissue. J Neurosurg Spine 2007; 7(6):601-9

3. Milhorat TH, Bolognese PA, Nishikawa M et al. Association of Chiari malformation type 1 and tethered cord syndrome: preliminary results of sectioning filum terminale. Surg Neurol. 2009; 72(1):20-35

4. Health Quality Ontario. Positional Magnetic Resonance Imaging for People With Ehlers-Danlos Syndrome or Suspected Craniovertebral or Cervical Spine Abnormalities: An Evidence-Based Analysis. Ont Health Technol Assess Ser. 2015 Jul 1;15(13):1-24. eCollection 2015.


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