“When symptoms such as headaches, dizziness, and fatigue persist, they often rob a person of their quality of life. Though not everyone experiencing these symptoms is suffering from Chiari I Malformation, for those that are, we’re here to provide answers and options. We’re here to help.” – John Oró, MD 

Symptoms from the Chiari I malformation often develop in a slow and insidious manner. The symptoms are often vague and progress slowly over a number of years. Many patients have symptoms for years before they are diagnosed with the Chiari I Malformation. About 1 out of 4 patients develop symptoms after trauma. The trauma is often mild or moderate in nature. Patients have reported accidents such as a falling off a trampoline, falling off a porch, accidentally hitting the back of their head or falling while riding a bicycle.

Many researchers believe that the Chiari malformation results from underdevelopment of the lower part of the skull. The Posterior Fossa is too small and does not provide the room needed for the Cerebellum and the lower brain stem. Thus, the lower part of the cerebellum, and sometimes the lower part of the brain stem, develops below the foramen magnum.

Magnetic resonance imaging (MRI) has revolutionized  the diagnosis of many disorders. It gives detailed pictures of the brain, the spinal cord, and the surrounding tissues. The MRI of patients with the Chiari I Malformation will show crowding of the foramen magnum at the bottom of the skull.

Shown above are two MRI scans. The scan on the left is normal and shows spinal fluid below the Cerebellum. The MRI on the right is that of a patient with the Chiari I Malformation. The Tonsils hang down below the foramen magnum and crowd out the spinal fluid space.

In 1891, Hans von Chiari, Professor of Morbid Anatomy at Charles University in Prague, published a report describing three types of brain malformations:

The Chiari malformation Type I (CMI) consists of hanging down (Herniation) of the cerebellar Tonsils into the upper Cervical spinal canal. In some cases the lower brain stem also hangs down into the spinal canal.

In the Type II malformation (almost always associated with spina bifida), the lower brain stem, cerebellar vermis, and tonsils hang down below the foramen magnum.

In the very rare Type III malformation the tissues of the Posterior Fossa are displaced into a soft sac (meningocele) at the back of the head and upper neck.

The inside of the skull (called the intracranial space) is partly separated into two compartments by a tent like structure called the tentorium. The large compartment above the tentorium is called the supratentorial compartment and the compartment below the tentorium is called the infratentorial compartment (supra means above, and infra means below). Most doctors call the infratentorial compartment the Posterior Fossa.

Chiari I malformation is an uncommon congenital (present at birth) disorder in which the Posterior Fossa (rear cranial cavity) is not large enough and, as a result, causes the lower part of the Cerebellum (referred to as the “Tonsils” of the brain) to protrude down into the spinal canal. This results in tissue compression and hinders normal spinal fluid flow. Although the Chiari (pronounced kee-ar'-ee) I malformation can cause problems in childhood, many people with this disorder do not do not develop symptoms until adulthood.