Chiari malformation

What is a Chiari malformation?

A Chiari malformation is a structural problem where the lowest part of your brain, called the cerebellum, is pushed down into the top of your spinal canal through an opening in the base of your skull. This can put pressure on your brain and spinal cord, and block the normal flow of the fluid that cushions them.

Symptoms of a Chiari malformation

Many people with a Chiari malformation, especially a mild type 1, have no symptoms at all. When symptoms do appear, they typically include:

• headaches at the back of the head, often triggered or made worse by coughing, sneezing, straining or bending over
• neck pain
• dizziness and balance problems
• muscle weakness, or numbness and tingling in the arms or legs
• blurred or double vision, and sensitivity to light
• swallowing problems, hoarseness or a change in your voice
• hearing loss and tinnitus (ringing in the ears)
• feeling or being sick
• difficulty sleeping, including sleep apnoea
• problems with memory or concentration.

These symptoms can also affect your mood, and some people develop depression as a result. In babies born with the rarer type 2 form, symptoms are usually more serious and can include a weak cry, pauses in breathing, swallowing difficulties, and arm or facial weakness.

Causes and who is at risk

In most cases, a Chiari malformation happens because part of the skull didn't grow large enough during development in the womb, so the brain becomes crowded and the cerebellum is pushed down. This is present from birth, even though symptoms might not appear until later in life, often in your 20s or 30s.

Much less commonly, it can develop later in life if too much spinal fluid drains away, due to injury, infection, or exposure to harmful substances.

It can sometimes run in families, and researchers think a faulty gene may be involved in some cases, though the overall risk of passing it on to your children is small.

It's thought to affect around 1 in every 1,000 people, though this may be an underestimate now that MRI scans are more widely used and can pick up cases that don't cause symptoms. It affects around three times more women than men.

Are there different types of Chiari malformation?

Yes. Doctors classify Chiari malformations into types, based on how much brain tissue is displaced and what other structures are involved:

• Type 1: The most common type. The lower part of the cerebellum extends into the opening at the base of the skull. It's often found by chance in teenagers or adults, and sometimes causes no symptoms at all
• Type 2: Also called Arnold-Chiari malformation: both the cerebellum and part of the brainstem extend down. This type is present from birth and almost always occurs alongside myelomeningocele, a serious form of spina bifida
• Type 3: A rare and very serious form, where brain tissue pushes through an abnormal opening in the back of the skull. It's usually identified at birth and can be life-threatening
• Type 4: A very rare type, where the cerebellum doesn't develop properly, or parts of it are missing.

Some specialists also describe a type 0 (crowding at the base of the skull without the cerebellum itself extending down) and a type 1.5 (a stage between type 1 and type 2), though these are newer, less established categories.

How is a Chiari malformation diagnosed?

There's no blood test or single test that confirms a Chiari malformation. Because symptoms are so varied, and can overlap with conditions such as migraine, fibromyalgia, chronic fatigue syndrome or multiple sclerosis, it can sometimes take a while to reach the right diagnosis.

Your doctor will ask about your symptoms and carry out a physical and neurological examination, checking things like your balance, reflexes, sensation, and eye movements. You may also be referred for a hearing or vision assessment, or a sleep study.

Imaging is the main way to confirm a diagnosis:

• MRI scan: This is the most useful test as it shows how far the cerebellum extends into the spinal canal, and can also show a build-up of fluid in the spinal cord (syringomyelia)
• Cine MRI: This is a specialised scan that captures the flow of spinal fluid as a moving image, to check whether, and how much, it's being blocked
• CT scan or X-ray: These can be used to look at the bones of the skull and spine, for example to check for thickening or instability.

Occasionally, a Chiari malformation is picked up on a scan done for a completely different reason, or on an ultrasound during pregnancy.

How is a Chiari malformation treated?

Non-surgical treatment

If you don't have any symptoms, you probably won't need treatment, just regular check-ups and imaging to monitor whether anything changes. For mild symptoms, options include:

• pain-relieving or anti-inflammatory medicines for headaches and neck pain
• physical therapy or massage
• hearing aids or glasses, if hearing or vision are affected
• a sleep study and treatment such as CPAP, if you have sleep apnoea
• keeping to a healthy weight, and staying active with low-impact exercise such as walking, cycling or swimming.

Some activities are best avoided if you have a Chiari malformation, since they put extra strain on the neck. These include high-velocity chiropractic neck manipulation, trampolines, roller coasters, scuba diving, contact sports, and straining during bowel movements.

If you're pregnant, or planning to become pregnant, let your obstetrician and neurosurgeon know, as pushing during childbirth can also increase the herniation.

Surgical treatment

If your symptoms are more severe, getting worse, or you have a related problem such as syringomyelia (a fluid-filled cavity in the spinal cord) or hydrocephalus (fluid on the brain), surgery may be recommended.

The main operation is called posterior fossa decompression surgery. Under general anaesthetic, the surgeon makes a cut at the back of your head and removes a small piece of bone from the base of your skull, sometimes together with a small piece of bone from the top of your spine. This creates more space, relieving pressure and helping fluid flow normally again. The surgeon may also open the covering of the brain (the dura) and sew in a patch to enlarge it further.

Other procedures that may be used include:

• A shunt: A thin tube that drains excess fluid away, used for hydrocephalus or a persistent syrinx
• Endoscopic third ventriculostomy (ETV): A small hole made in the brain to release trapped fluid, as an alternative to a shunt
• Untethering: Separating a spinal cord that's abnormally attached (tethered) within the spine
• Spinal fixation: Stabilising the spine with surgery, for people who also have a hypermobility condition such as Ehlers-Danlos syndrome.

Surgery aims to stop your symptoms getting worse, and many people also see an improvement, particularly in headaches, though this isn't guaranteed and headaches specifically aren't always fully resolved by surgery.

As with any operation, there are risks, including a small chance of paralysis, stroke, infection, or the symptoms not improving or getting worse. Your neurosurgeon will talk you through the risks and benefits that apply to your specific situation.

When should I see a doctor?

If you've been diagnosed with a Chiari malformation, contact your doctor if you notice any new symptoms, or if your existing symptoms get worse. Keeping a symptom diary, noting how you feel day to day, can help you spot patterns and describe changes clearly at your appointments.

Because symptoms can be vague and easily mistaken for other conditions, it's worth persisting with your doctor if you don't feel you're getting clear answers, particularly if you have several of the symptoms above together.