T2 W MR sagittal cervical spine image shows herniation of cerebellar tonsils with extensive syrinx in cervical and dorsal spinal cord.
Chiari I malformation (CMI) is characterized by herniation of the cerebellar tonsils through the foramen magnum into the cervical spinal canal. The cerebellar tonsils often are elongated and peglike. Mild caudal displacement and flattening or kinking of the medulla may be present. The vermis cerebelli and the fourth ventricle are normal or only minimally deformed. Its symptoms may result in occipital headache, difficulty swallowing, numbness and tingling in the hands.
Distention with cerebrospinal fluid (CSF) of the central canal of spinal cord (ie, hydromyelia) or paracentral cavities (Syringomyelia) is present in approximately 25% of patients with CMI. The cervical cord is the most common site of syringohydromyelia.
Classification:
| Type | Presentation | Other notes |
|---|---|---|
| I | Is generally asymptomatic during childhood, but often manifests with headaches and cerebellar symptoms. Herniation of cerebellar tonsils. | The most common form. |
| II | Usually accompanied by a myelomeningocele leading to partial or complete paralysis below the spinal defect. Abnormal development of the cerebellar vermisand medulla oblongata occur, and they both descend into the foramen magnum. Hydrocephalus is frequently present. | |
| III | Causes severe neurological defects. It is associated with an encephalocele. | |
| IV | Characterized by a lack of cerebellar development. |
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