Chiari malformation type 1 is a structural abnormality of the cerebellum, the part of the brain that controls balance, and the skull. 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. It is usually first noticed in adolescence or adulthood, often by accident during an examination for another condition. 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. Depending on the symptoms present and severity, some individuals may not require treatment while others may require pain medications or surgery.

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. Click here to view a diagram of the spine.

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.

The prognosis for someone diagnosed with Chiari malformation type 1 is often unknown. Many people with this condition do not have any symptoms, and it is not possible to predict if symptoms will develop in the future. Other people with Chiari malformation may experience dizziness, muscle weakness, numbness, vision problems, headache, or problems with balance and coordination. In these people, it is not always known if symptoms will get worse over time. It is important for people with Chiari malformation type 1 to receive regular medical care so they can be monitored by a physician for any new symptoms.

There are some treatments that may help reduce or eliminate the symptoms of Chiari malformation type 1. Medications may ease certain symptoms, such as pain. Surgery is another treatment option, but it is typically reserved for people with severe symptoms. Many patients who have had surgery see a reduction in their symptoms and/or prolonged periods of relative stability.