Chiari 1 Malformation

Diagnosis: Chiari 1 Malformation 

Clinical Keywords: Chiari 1, tonsillar herniation, foramen magnum crowding, cord syrinx, headache 

Clinical Problems: 

1. Source of headache 

2. Presence may lead to cord syrinx, hydrocephalus 

In Plain Language: 

The brain is primarily made up of the cerebral cortex, brainstem, and cerebellum. The bottom parts of the cerebellum on each side are called the cerebellar tonsils. They sit above the hole at the bottom of the skull called the foramen magnum where the brainstem becomes the spinal cord and the cord then goes into the neck.

Sometimes, the cerebellar tonsils can dip down through the hole and cause crowding which can lead to symptoms such as headache. Any dip of the tonsils more than 5 millimeters is called a Chiari 1 malformation and it is considered something that happens from birth or as we age.

Tonsils below the foramen magnum can cause crowding which may result in headache, arm numbness or weakness, and/or back-up of fluid into the brain or spinal cord. 

Medical Description: 

The human brain is primarily composed of the large cerebral cortex, the brainstem, and the cerebellum. In inferior parts of the cerebellum on either side of the midline are called the cerebellar tonsils and they usually reside directly above the foramen magnum. Normally, there is ample space for the brainstem to become the spinal cord without any crowding or narrowing. 

A Chiari 1 malformation is a defect in which the cerebellar tonsils herniate below the foramen magnum into the cervical spine region resulting in crowding and possible compression of the spinal cord. Herniation greater than 5 mm below the foramen magnum is considered a Chiari 1 malformation and less than 5 mm is called “low lying tonsils” which is usually an asymptomatic finding. While Chiari 1 malformations may also be asymptomatic, they can lead to: 

• Headache: tonsillar herniation can distort the normal flow of cerebrospinal fluid which can result in headaches 
• Cord syrinx: Fluid-filled expansion of the central canal of the spinal cord which can lead to upper extremity symptoms of numbness, tingling, and/or weakness if large. 
• Hydrocephalus: Narrowing of the foramen magnum can result in a build-up of cerebrospinal fluid in the brain resulting in too much fluid 

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