Chiari malformation type 1

Alternate names

Chiari type I malformation; Chiari malformation type I; Arnold Chiari malformation type I; Arnold-Chiari malformation type 1; Arnold-Chiari malformation type I

Definition

Chiari malformation type 1 is a structural abnormality of the cerebellum, the part of the brain that controls balance, and the skull.

Summary

• The malformation occurs when the lower part of the cerebellum extends below the foramen magnum (the large hole at the base of the skull which allows passage of the spinal cord), without involving the brainstem.
• Normally, only the spinal cord passes through the foramen magnum.
• Type 1 is the most common type of Chiari malformation and may not cause any symptoms.

Cause

• Primary or congenital Chiari malformations are caused by structural defects in the brain and spinal cord that occur during fetal development.
• The underlying cause of the structural defects are not completely understood, but may involve genetic mutations or lack of proper vitamins or nutrients in the maternal diet.
• Less frequently, Chiari malformation type 1 is acquired after birth.
• Causes of acquired Chiari malformation type 1 involve the excessive draining of spinal fluid from the lumbar or thoracic areas of the spine as a result of injury, exposure to harmful substances, or infection.

Onset

It is usually first noticed in adolescence or adulthood, often by accident during an examination for another condition.

Signs and symptoms

Symptoms, when present, may include headache, neck pain, unsteady gait, poor hand coordination, numbness and tingling of the hands and feet, dizziness, difficulty swallowing, and vision and speech problems.

Clinical presentation

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed.

100% of people have these symptoms

• Arnold-Chiari type I malformation

80%-99% of people have these symptoms

• Neck pain
• Recurrent paroxysmal headache
• Small posterior fossa

30%-79% of people have these symptoms

• Abnormality of the clivus
• Abnormality of the eleventh cranial nerve
• Abnormality of the twelfth cranial nerve
• Abnormality of the vestibulocochlear nerve
• Anteriorly placed odontoid process
• Areflexia of upper limbs
• Cervical C2/C3 vertebral fusion
• Cranial nerve compression
• Cranial nerve paralysis
• Distal peripheral sensory neuropathy
• Dysesthesia
• Dysphagia(Poor swallowing)
• Gait ataxia(Inability to coordinate movements when walking)
• Increased intracranial pressure(Rise in pressure inside skull)
• Lower limb hyperreflexia(Overactive lower leg reflex)
• Myelopathy
• Nystagmus(Involuntary, rapid, rhythmic eye movements)
• Progressive cerebellar ataxia
• Scoliosis
• Sensory impairment
• Stiff neck(Neck stiffness)
• Syringomyelia(Fluid-filled cyst in spinal cord)
• Tinnitus(Ringing in ears)
• Vertigo(Dizzy spell)
• Vocal cord paralysis(Inability to move vocal cords)

5%-29% of people have these symptoms

• Abnormality of the musculature of the lower limbs
• Adult onset sensorineural hearing impairment
• Babinski sign
• Basilar impression
• Basilar invagination
• Brain stem compression
• Central sleep apnea
• Diplopia(Double vision)
• Fatigable weakness of swallowing muscles
• Photophobia(Extreme sensitivity of the eyes to light)
• Urinary incontinence(Loss of bladder control)

Diagnosis

Many people with Chiari malformations have no symptoms and their malformations are discovered only during the course of diagnosis or treatment for another disorder. The doctor will perform a physical exam and check the person's memory, cognition, balance (functions controlled by the cerebellum), touch, reflexes, sensation, and motor skills (functions controlled by the spinal cord). The physician may also order one of the following diagnostic tests:

• Magnetic resonance imaging (MRI) is the imaging procedure most often used to diagnose a Chiari malformation. It uses radio waves and a powerful magnetic field to painlessly produce either a detailed three-dimensional picture or a two-dimensional “slice” of body structures, including tissues, organs, bones, and nerves.
• X-rays use electromagnetic energy to produce images of bones and certain tissues on film. An X-ray of the head and neck cannot reveal a CM but can identify bone abnormalities that are often associated with the disorder.
• Computed tomography (CT) uses X-rays and a computer to produce two-dimensional pictures of bone and blood vessels. CT can identify hydrocephalus and bone abnormalities associated with Chiari malformation.

Treatment

• Some individuals with Chiari malformation type 1 do not have symptoms and do not require treatment.
• People who have mild symptoms, without syringomyelia, can typically be treated conservatively. Mild neck pain and headaches can usually be treated with pain medications, muscle relaxants, and the occasional use of a soft collar.
• People with more severe symptoms may need surgery.
• Surgery is the only treatment available to correct functional disturbances or stop the progression of damage to the central nervous system.
• The goals of surgical treatment are decompression of the point where the skull meets the spine (the cervicomedullary junction) and restoration of normal flow of cerebrospinal fluid in the region of the foramen magnum (the hole in the bottom of the skull where the spinal cord passes to connect to the brain).
• Prognosis after surgery for the condition is generally good and typically depends on the extent of neurological deficits that were present before the surgery. Most people have a reduction of symptoms and/or prolonged periods of relative stability. More than one surgery may be needed to treat the condition.

NIH genetic and rare disease info

• NIH info on Chiari malformation type 1

Chiari malformation type 1 is a rare disease.

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