Sagittal MRI. Cerebellar tonsils dip below the foramen magnum.
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Chiari Malformation
Overview
- Chiari malformation is a wide-ranging syndrome, which involves displacement of the cerebellar tonsils through the foramen magnum and other potential structural anomalies.
- It is divided into three different subtypes: types I (the most mild), type II, and type III (the most severe).
- Patients with Chiari malformation range from being entirely asymptomatic (when the malformation is only incidentally found on radiographic imaging) to being severely affected with considerable developmental delay and substantial motor and sensory deficits.
- Chiari malformation morbidity is determined by:
- The degree of cerebellar displacement.
- The degree of displacement of additional brainstem structures.
- The associated pathologic involvement of other areas of the central nervous system.
Chiari Malformation and Association with Syringomyelia and Myelomeningocele
- Type I Chiari malformation is found in roughly two-thirds of cases of syringomyelia (a central cavitation of the spinal cord).
- Type II Chiari malformation (aka Arnold-Chiari malformation) is almost universally associated with myelomeningocele.
- Myelomeningocele is a protrusion of the spinal cord and meninges through a defect in the posterior vertebral column.
Chiari Malformation and Basilar Invagination (aka Basilar Impression)
- Basilar invagination (aka basilar impression) is a craniocervical junction abnormality wherein the tip of the odontoid process projects superior to the foramen magnum and it manifests with a short neck on physical exam. It's seen in Chiari malformation and also in more rare skeletal anomalies, including:
- Achondroplasia
- Klippel-Feil syndrome
- Osteogenesis imperfecta
- Cleidocranial dysostosis