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Medical College of Wisconsin Chiari Malformation Program

Advancing the diagnosis and treatment of Chiari Malformation and related disorders.

Program Details

What is Chiari Malformation?
Chiari malformation is a congenital (i.e., present at birth) structural problem at the base of the skull that affects the brain and spinal cord. In fact, it is not a malformation of the brain at all. More accurately, the lower portion of the skull, the portion known as the posterior fossa, is too small to accommodate the lower portion of the brain. As a result, the portion of the cerebellum called the tonsil is forced to protrude into the spinal column. This results in a compression of the brainstem and spinal cord. It is the compression of the brainstem and spinal cord that is primarily responsible for the symptoms. We have learned that even minimal protrusion of the cerebellar tonsils can cause symptoms.
Our Approach to Chiari Malformation

Chiari malformation has always been classified as a rare disease and is officially reported to occur in less than 1% of the population. The actual occurrence of Chiari malformation in the general population is in fact unknown. Why? First, we do not yet know how to best define the problem. Second, many neurosurgeons with extensive experience in treating Chiari malformation have come to learn that the current criteria for diagnosing Chiari on an MRI scan are much too strict. As a result, many patients go undiagnosed. Rather than focus on the position of the cerebellar tonsils as shown on the MRI scan, we have come to view the problem as the result of the compression of the brainstem or spinal cord at the base of the skull. This may occur even if the tonsils of the cerebellum protrude through the foramen magnum by as little as 1 mm. In fact, patients with the smaller Chiari malformations may have more symptoms than those with the larger Chiari malformations.

Our studies have shown that the neurological symptoms of Chiari malformation may also occur because of other disorders such as cervical stenosis, tethered cord syndrome, and syringomyelia. These different disorders may occur independently of Chiari malformation but frequently occur in conjunction with the Chiari malformation.

We have to prioritize the conditions that we diagnose from the most severe to the least severe. In this manner, we can select that treatment that is likely to have the greatest benefit for the patient. Each of these conditions is diagnosed by MRI imaging. Newer imaging techniques, some developed by Dr. Heffez and his radiology colleagues, have improved our ability to recognize brainstem compression and spinal cord compression

Signs & Symptoms

Despite the fact that Chiari malformation is usually present at birth, the symptoms of the malformation are not usually experienced until adulthood. Chiari malformation is often difficult to diagnose because the symptoms can be vague and so numerous that many doctors just cannot make sense of them.

The symptoms of Chiari malformation include, but are not limited to:

  1. Headache - This is the most common symptom of Chiari malformation. Headache is often pressure-like and usually begins at the back of the head, often radiating behind the eyes. Coughing, laughing, bending forward, sneezing or looking up can worsen the headache. Headache may be confused with a migraine.
  2. Neck pain - Often pressure-like and radiating down the spine and across the shoulders
  3. Dizziness, vertigo - Often worsened by extension of the neck
  4. Vague pains throughout the body
  5. Impaired balance
  6. Clumsiness
  7. Chronic nausea
  8. Foggy thinking, poor memory and concentration
  9. Frequent or urgent urination
  10. Irritable bowel syndrome
  11. Auditory symptoms - Including ringing in ears, increased sensitivity to sounds
  12. Difficulty swallowing
  13. Changes in the voice - This can include hoarseness or inability to regulate the voice when shouting or singing
  14. Visual symptoms - Including double vision, sensitivity to light, and seeing floaters
Types of Chiari Malformation
There are three types of Chiari malformation. Type I relates to the extension of the cerebellar tonsils into the foramen magnum and below causing compression of the brainstem. This manifests in adult life and is the Chiari malformation that we treat at this clinic. Type II and type III are much more extreme disorders that are present, diagnosed and treated at birth. Some people describe Chiari zero malformation. This is simply a malformation with cerebellar tonsils that do not protrude by standard 5 mm. Many of our patients fall into this category.
Testing & Diagnosis

The diagnostic process begins with a complete medical history and physical examination. These are followed by a complete neurological evaluation that will assess your specific symptoms and neurological function. The patient with a Chiari malformation may have an entirely normal examination. In such cases, it becomes more difficult to determine if the Chiari is indeed a problem and if surgery is indeed the best solution. In such cases, judgment of an experienced neurosurgeon becomes very important. When the neurological examination is abnormal, the pattern of abnormal findings can make it easy to pinpoint the problem to the cervical spinal cord and brainstem.

Patients may have difficulty with coordination, balance, eye movement, sensation, and strength. The reflexes may be too active or not active enough. Other reflexes that are never present except when the spinal cord is not functioning normally—pathological reflexes—may also be detected.

Magnetic resonance imaging (MRI) is the best diagnostic tool for detecting Chiari malformation. This test provides the doctor with detailed anatomical information regarding the structure of the base of the brain. The criteria for diagnosing Chiari malformation, however, are very arbitrary. As a result, some doctors adhere to a rigid standard—5 mm of tonsillar herniation—before making the diagnosis of Chiari, even in the face of typical patient symptoms and obvious neurological findings. Hence, many patients with Chiari go undiagnosed and untreated for years. We have developed some MRI imaging strategies that demonstrate the critical problem—brainstem compression—more clearly. These MRI techniques allow us to identify some Chiari patients who would otherwise go undiagnosed.

What Happens if Your Symptoms Reoccur?

Some patients may undergo Chiari surgery by another surgeon and either fail to experience any improvement in symptoms or, worse, they may deteriorate. This is considered failed Chiari surgery. Perhaps 20% of patients that I have treated have been treated elsewhere with poor results. There are several possible explanations:

  1. Excessive bone removal causing slumping or further settling of the cerebellar tonsils and causing the Chiari problem to recur after initial improvement.
  2. Failure to do a dural patch, resulting in inadequate decompression of the brainstem.
  3. Failure to perform intradural exploration, leaving compression of the brainstem unresolved.
  4. CSF leak with pseudomeningocele formation which results in headache, dizziness, nausea whenever the patient is upright. In addition, the CSF leakage can promote further settling of the brain and recurrence of the Chiari malformation.
  5. Failure to recognize cervical stenosis, which can mimic all the symptoms of the Chiari malformation.
  6. Failure to recognize and treat lumbar tethered spinal cord, which occurs in 20% of patients with Chiari.

All of these problems can be corrected and the patient can go on to have an excellent result.


Some people with Chiari malformation have no symptoms and do not require treatment.

Some symptoms of Chiari malformation such as headache and dizziness at times may be effectively treated by medication. Medication alone will not correct the root cause of the symptoms—brainstem compression. As a rule, when Chiari malformation causes symptoms that seriously impair the patient's quality of life, it is best to consider surgery.

Surgery for Chiari malformation is basically about creating more room for the brain. Surgery relieves the compression of the brainstem and spinal cord and improves the circulation of spinal fluid.

Neurosurgery Chiari Malformation Program Faculty


Saman Shabani, MD

Assistant Professor; Director, Spinal Oncology Surgery; Director, Adult Spinal Deformity Surgery; Co-Director, Spine Fellowship Program