Children's Hospital Colorado

Chiari Malformation

What is Chiari malformation (CMI)?

A Chiari malformation is an abnormal connection between the bottom of the brain and the spinal column. In the most common type of Chiari malformation, Type I (called CMI), the structure at the bottom of the brain, called the cerebellar tonsils, extends past the bottom of the skull and into the spinal canal. Sometimes the malformation can include more structures of the brain and is considered a more serious form of the condition.

What are the types of Chiari malformation?

There are four different types of Chiari malformation (I, II, III and IV).  Although they share some characteristics, they are very different. Type I is by far the most common in children. Ten to 20% of patients with CMI also have scoliosis, an abnormal curvature of the spine, or a syrinx, a pocket of fluid that collects in the spinal cord. These conditions often contribute to the patient's symptoms and findings during a neurological exam.

What causes Chiari malformation?

Current research indicates that CMI usually happens when the volume of the inside of the back or bottom of the skull is too small to hold all the neural tissue within it. As a result, a small portion of the bottom of the cerebellum, the back of the brain, pushes downwards into the spinal canal.

Current research does not suggest that there are any environmental or maternal risk factors that cause CMI.

Who gets Chiari malformation?

Because most children with CMI have no symptoms and do not require therapy, the exact number of patients with the condition is not known. Some sources estimate that 3% of the total population has Chiari malformation.

While no gene or gene combination has been correlated with CMI, occasionally families have more than one member with CMI. There are some genetic syndromes that include CMI, which indicates that people with some genetic profiles may be more likely to develop the condition.

Get to know our pediatric experts.

Kelly Knupp, MD

Kelly Knupp, MD

Neurology - Pediatric, Neurophysiology, Neurology

Corbett Wilkinson, MD

Corbett Wilkinson, MD

Neurosurgery, Neurosurgery - Pediatric

Teri Schreiner, MD, MPH

Teri Schreiner, MD, MPH

Neurology - Pediatric

Megan Barry, DO

Megan Barry, DO

Neurology - Pediatric, Vascular Neurology