Chiari malformation is an abnormality or structural defect in the cerebellum, the lower part of the brain in the back of the head that controls balance. The indented space at the base of the skull, above the foramen magnum, is a funnel-like opening to the spinal canal that normally holds the cerebellum and parts of the brainstem. A Chiari malformation occurs if part of the cerebellum extends below the foramen magnum.


There is no known cause for primary Chiari malformations. However, acquired or secondary Chiari malformations may arise from excessive drainage of spinal fluid from the lumbar or thoracic areas of the spine due to injury, exposure to harmful substances, or infection.

  • Primary or congenital Chiari malformation: structural defects in the brain and spinal cord that occur during fetal development
  • The bony space is typically deformed or smaller than normal, and the normal structures are crowded and compressed

Graphic image courtey of


Risk factors are traits or lifestyle habits associated with an increased chance of developing a disease or condition. There are no known risk factors for Chiari malformation.

Chiari malformation can become a progressive disorder and lead to serious complications:

  • Hydrocephalus: accumulation of excess fluid within the brain
  • Syringomyelia: a cavity or cyst (syrinx) forms within the spinal column
  • Paralysis, which may occur due to the crowding and pressure on the spinal cord, tends to be permanent, even after treatment with surgery
  • Death: an uncommon outcome, usually early in infancy, when a child is born with severe congenital abnormalities in other parts of the central nervous system


Chiari malformations are classified by type, depending on their severity, and symptoms vary according to the type.

Symptoms that may occur with any of the three types:

  • Headaches, often severe, typically precipitated with sudden coughing, sneezing, or straining
  • Neck pain
  • Muscle weakness
  • Numbness in arms, legs, or face
  • Problems with balance and coordination
  • Double or blurred vision
  • Dizziness
  • Swallowing difficulties
  • Hydrocephalus
  • Syringomyelia or syrinx (a cyst within the spinal cord); this may cause weakness, numbness, tingling and/or clumsiness involving the upper and lower extremities
  • Spinal curvature

Type I

  • Sometimes asymptomatic-often found by accident during an examination for another condition
  • Patients are usually in their mid- to late-thirties at diagnosis The syndrome is somewhat more common in women

Type II

  • A greater amount of tissue protrudes into the spinal canal compared with Type I
  • Myelomeningocele: the spinal canal and backbone do not close before birth, causing the spinal cord to protrude through an opening in the back. This can cause partial or complete paralysis below the spinal opening.

Type III

  • Severe neurological defects
  • A portion of the lower back part of the brain (cerebellum) or the brainstem extends through an abnormal opening in the back of the skull


Diagnosis usually involves a thorough neurological exam and radiological imaging.

  • Complete physical examination in which the physician takes a medical history and asks whether symptoms such as head and neck pain are present; physician will also conduct a check of fine motor skills, reflexes, memory, cognition, balance, and cranial nerve function
  • Magnetic resonance imaging (MRI) is the imaging procedure most often used to diagnose a Chiari malformation
  • Computed tomography (CT scan) can identify hydrocephalus and bone abnormalities associated with Chiari malformation
  • X-ray of head and neck: can detect bone abnormalities often associated with Chiari malformation but cannot detect the Chiari malformation itself


Treatment depends on the severity and characteristics of your condition.

  • Monitoring with regular examinations for those with no symptoms
  • Headache and pain management with pain medication, physical therapy or a reduction in activities can help manage symptoms
  • Primary surgical repair to reduce pressure on the cerebellum and the spinal cord and restore the normal flow of spinal fluid

The most common operation for Chiari malformation is posterior fossa craniectomy or posterior fossa decompression during which the surgeon removes a small section of bone in the back of the skull and possibly the upper cervical spine, relieving pressure by giving the brain and brainstem more room.

Medications may ease certain symptoms, such as pain, but surgery is the only treatment available to correct functional disturbances or halt the progression of damage to the central nervous system. Primary repair of the Chiari malformation is frequently all that is required. Occasionally the hydrocephalus or spinal syrinx do not go away and require separate shunting procedures.

Case Study

One such patient was a man in his mid-thirties with a history of severe, progressive headaches that were made worse by coughing, bending, and stooping. He had noticed a change in the quality of his voice and a difficulty swallowing. He also found himself gasping for breath on occasion. His workup led to an MRI scan (left), which demonstrated a severe Chiari malformation associated with compression of the cervicomedullary junction and a large cervical syrinx. After decompressive surgery and recovery, the patient returned home and noticed almost immediate improvement in his symptoms. He continued to improve and returned to his normal work schedule.

Preoperative MRI showing hydrocephalus, herniation of cerebellar tonsils and spinal syrinx

Postoperative MRI showing decrease in hydrocephalus, return to normal position of cerebellar tonsils, and resolution of syrinx

MRI images used with permission from Joshua B. Bederson, MD


There is no known way to prevent Chiari malformations.


To learn more about Chiari malformations call the Mount Sinai Department of Neurosurgery at 212-241-2377.

Written by the Mount Sinai Department of Neurosurgery.

This information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. Call you health care provider immediately if you think you may have a medical emergency. Always seek the advice of your physician or other qualified health provider before starting any new treatment or with any questions you may have regarding a medical condition.