What is a Chiari malformation?

Chiari malformation is a group of several disorders in which there is an abnormal shape or position of part of the brain near the base of the skull. The most common type by far is the Chiari I malformation, which we will focus on here.

Chiari I occurs when the cerebellar tonsils descend beneath the bottom of the skull through an opening called the foramen magnum (see image below). The foramen magnum is the hole in the skull where the brainstem passes down and becomes the spinal cord. When the cerebellar tonsils sit lower than normal and occupy part of the upper spinal canal, they can squeeze or compress the back of the brainstem, causing symptoms.

Chiari I is considered a congenital or developmental disorder, meaning that a person is born with it, though there are some examples of it developing later in life. Many patients do not experience symptoms until young adulthood or even later. Chiari I is estimated to affect roughly 1 in 1000 people.

What are the symptoms?

Many patients with Chiari I never develop symptoms. For those who do, the most common symptoms are headache and neck pain near the base of the skull. In particular, the headache and neck pain tend to be brought on or worsened by activities such as coughing, sneezing, laughing, straining, or exercising. Other symptoms may include nausea and vomiting, sleep apnea, difficulty swallowing, balance problems, tinnitus (ringing in the ears), double vision, and changes in the sensation or strength in the arms, among others.

How are Chiari malformations diagnosed and treated?

Chari I can be diagnosed after a careful medical history, physical examination, and review of a scan of your brain (usually an MRI).

The primary treatment for Chiari I is surgery, often referred to as a Chiari decompression or suboccipital craniectomy. The goal of this procedure is to open up space around the cerebellar tonsils so that they are no longer pushing against the back of the brainstem.

Surgery consists of shaving away bone at the base of the skull in an effort to widen the foramen magnum. Sometimes part of the back of the first cervical vertebrae (C1) is also removed. The amount of bone removal depends on how low the tonsils descend. I also open and expand the covering around the brain called the dura. This helps ensure that there is absolutely no source of compression remaining, since the dura can constrict the tonsils and brainstem even if the bone is removed.

What can a patient expect after a Chiari decompression?

Most patients stay in the hospital two or three nights, depending on how they feel. The muscles in the back of the neck near the base of the skull tend to be sore or stiff for a few weeks after the operation. Relief from Chiari symptoms tends to occur quickly, though it can sometimes be hard to tell in the beginning due to pain from the incision. It's important to discuss with me in the office which of your symptoms are most bothersome to you and whether they are likely to respond to surgery.