Chiari malformation is a condition where the bottom part of the cerebellum (the “tonsils”) protrudes down into the upper spinal canal. The herniated tissue blocks the circulation of cerebrospinal fluid in the brain and can lead to the formation of a cavity (syrinx) within the spinal cord. There are four types of Chiari malformations.
- Chiari I malformation describes low-lying cerebellar tonsils without other congenital brain malformations. This is the most prevalent form and it is generally considered to be a congenital malformation. It is rarely apparent at birth
- Chiari 2 malformation is a more severe malformation that is apparent at birth and is associated with complex defects of the brain and spinal cord
- Type 3 and Type 4 Chiari malformations are extremely rare
Patients with Chiari 1 malformations usually present with pain, especially pressure like headaches in the back of the head, aggravated by coughing and straining. They could also experience weakness, particularly in the hands, when there is associated syringomyelia (a cavity within the spinal cord). Other potential symptoms include neck, arm, and leg pain, numbness, loss of temperature sensation, unsteadiness, double vision, slurred speech, trouble swallowing, vomiting, dizziness, vertigo and tinnitus (ringing in the ears). As a result of the wide variety of symptoms that may be present, patients with Chiari 1 malformation are often misdiagnosed
In most cases the cause of Chiari 1 malformation is congenital (present at birth). In many cases the compartment of the brain holding the cerebellum (posterior fossa) is smaller than normal. In rare instances, abnormally low pressure in the spinal canal resulting from a lumboperitoneal shunt or condition called spontaneous intracranial hypotension, can pull the cerebellar tonsils downward. In addition, certain conditions that cause high pressure in the brain compartment can force the cerebellar tonsils downward. Some of these conditions include cerebellar brain tumors, hydrocephalus, posterior fossa arachnoid cysts and pseudotumor cerebri.
An MRI of the brain and cervical spine is the best diagnostic study to identify a Chiari malformation. The cervical portion of the study will also evaluate for the presence of syringomyelia which is present in 20-30 % of cases