The Chiari malformation is an abnormality in the lower part of the brain called the cerebellum. There are several different forms. The most common type is the Chiari I malformation (CM) which this article addresses. Less commonly, it may be known as Arnold-Chiari malformation, tonsillar herniation or tonsillar ectopia. Most cases of Chiari are congenital, meaning they are present from birth.
In normal anatomy, the cerebellar tonsils are located just above this (red) line called the foramen magnum. But in an individual with Chiari, the tonsils hang below the line (herniate) into the spinal canal. The degree to which the tonsils extend can vary tremendously.
The most common symptom of Chiari malformation is a headache, which begins at the back of the head (neck) and radiates upward. The pain is often made worse or can be brought on by coughing, sneezing or straining. These activities are known as valsalva maneuvers.
Visual problems such as nystagmus (involuntary eye movements), double or blurred vision may occur. Balance difficulties, vertigo and dizziness also may be present. Some people may have cranial nerve compression. This can result in apnea (cessation of breathing), gagging, swallowing difficulties, facial numbness or syncope (temporary loss of consciousness).
Patients may have muscle weakness, particularly in the upper extremities, coordination problems, and gait abnormalities. Imaging of the spine may reveal a fluid collection inside of the spinal cord, known as a syrinx. Some individuals may have hydrocephalus, a buildup of fluid in the ventricles of the brain.
The first step after diagnosis is to consult with a neurosurgeon who has experience treating and managing this disorder. Be aware that you may need to travel and you may wish to consult with more than one specialist.
If symptoms are mild and not progressing, your doctor may recommend conservative management. Supportive care such as headache and pain management, physical therapy or a reduction in activities can help manage symptoms.
An operation may be recommended. This is referred to as a posterior fossa decompression. The surgeon makes more room in the back of the head by removing small pieces of the skull bones. This reduces compression of the brain stem and allows the tonsils to move back into their natural position. The specific surgical techniques will vary among surgeons; no consensus yet exists on the best variation on this surgical procedure.
Researchers investigated the genetic implications of the Chiari malformation with or without syringomyelia. A genetic prevalence has been identified in some families. Researchers continue to search for the gene(s) that are responsible for producing the Chiari malformation.
MRI scanning is recommended for family members who have signs or symptoms of the disorder.