Chiari Malformation

What happens in Chiari malformation

The back of the skull (posterior fossa) holds the cerebellum and brainstem. In Chiari malformation, this space is often too small or crowded, so the cerebellar tonsils are pushed down through the foramen magnum, the large opening where the skull meets the spine. This can:

• block the normal pulsing flow of cerebrospinal fluid (CSF) between the brain and spine
• compress the brainstem, upper spinal cord and lower cranial nerves
• lead to a fluid-filled cavity in the spinal cord, called a syrinx (syringomyelia)

Tonsils extending 5 mm or more below the foramen magnum is the usual imaging definition of type I, though symptoms do not always match the measurement.

Types

Chiari can also be acquired, for example after repeated lumbar punctures or shunts that lower spinal fluid pressure, or in some connective tissue disorders.

Symptoms

Many people with type I Chiari have no symptoms. When present:

• Headache: at the back of the head and upper neck, brought on or worsened by coughing, sneezing, laughing, straining or bending, usually lasting seconds to minutes
• neck pain
• dizziness, poor balance and unsteady walking
• numbness, tingling or weakness in the arms and hands
• difficulty swallowing, choking, hoarseness
• tinnitus (ringing in the ears) and hearing changes
• abnormal eye movements, blurred or double vision
• sleep apnea
• in children: scoliosis, irritability, and in infants, feeding difficulties and breathing problems

With a syrinx, people may develop loss of pain and temperature sensation in a "cape" distribution across the shoulders and arms, and hand weakness.

Causes

Most type I Chiari malformations are thought to be present from birth, due to a small or abnormally shaped posterior fossa. Some run in families. Type II is linked to the development of spina bifida during pregnancy. Associations include Ehlers-Danlos syndrome, craniosynostosis and some skeletal disorders.

Diagnosis

• MRI of the brain and cervical spine: confirms the diagnosis and measures how far the tonsils descend.
• MRI of the whole spine: checks for a syrinx and tethered cord.
• CSF flow (cine) MRI: shows whether fluid flow is blocked.
• Neurological examination: reflexes, strength, sensation, coordination and cranial nerves.
• Sleep study and swallowing studies where relevant.

Because Chiari is commonly found by chance, a key step is deciding whether symptoms are actually caused by it.

Treatment

Observation

People without symptoms, or with mild headaches only, are usually monitored with periodic MRI and symptom review. Headaches can be managed with standard pain relief. Avoiding heavy straining helps some people.

Decompression surgery

Posterior fossa decompression is recommended for significant symptoms, brainstem compression, or a syrinx. The surgeon removes a small piece of bone at the back of the skull and sometimes part of the top vertebra, and often enlarges the covering membrane (duraplasty) to give the brain more space and restore CSF flow.

Most people with the classic cough headache improve. Other symptoms such as numbness or weakness may stabilize rather than resolve completely. Risks include CSF leak, infection, meningitis and the need for further surgery.

Treating associated conditions

• shunting for hydrocephalus in type II
• spina bifida care
• scoliosis treatment

Outlook

Many people with type I Chiari never need surgery. Those who do usually see improvement, particularly in headaches. Type II outcomes depend on the severity of the associated spina bifida and hydrocephalus.

Frequently asked questions

What are the symptoms of Chiari malformation?

The most typical symptom is a headache at the back of the head triggered by coughing, sneezing or straining. Others include neck pain, dizziness, poor balance, numbness or weakness in the hands, swallowing problems and ringing in the ears. Many people have no symptoms.

Is Chiari malformation serious?

It ranges from harmless to serious. Type I is often mild or symptom-free. Type II, with spina bifida, and Chiari with a syrinx or brainstem compression are more serious and often need surgery.

Can Chiari malformation go away?

The structural difference does not go away by itself, though symptoms may fluctuate. Mild cases may never cause problems. Surgery creates more room and can relieve symptoms.

What activities should I avoid with Chiari malformation?

Doctors may advise avoiding activities with heavy straining, such as maximal weightlifting, and contact sports with risk of neck injury, especially if you have symptoms. Discuss your specific activities with your neurosurgeon.