Chiari malformation

A Chiari malformation is a structural defect in the cerebellum, the part of the brain that controls balance. It involves the lower part of the cerebellum, known as the cerebellar tonsils, extending into the foramen magnum, the opening at the base of the skull through which the spinal cord passes.

Sagittal MRI scan of brain of patient with Chiari malformation

Classification

• Chiari malformations are classified into four types:
• Chiari I is the most common type and is often asymptomatic. Symptoms, if they occur, generally appear during adolescence or adulthood. This type involves herniation of the cerebellar tonsils into the foramen magnum.
• Chiari II, also known as Arnold-Chiari malformation, is associated with myelomeningocele, a form of spina bifida. Both cerebellar and brain stem tissue extend into the foramen magnum in Chiari II.
• Chiari III is a rare and severe malformation involving herniation of the cerebellum and brain stem into a spina bifida defect in the neck or upper back.
• Chiari IV involves an incomplete or underdeveloped cerebellum—a condition known as cerebellar hypoplasia. It's extremely rare and associated with poor outcomes.

Symptoms

Symptoms vary widely and depend on the type of Chiari malformation. Symptoms may include headaches, particularly after sudden coughing, sneezing or straining, problems with balance and coordination, dizziness, dysphagia, vision problems, and numbness or weakness in the limbs.

Diagnosis

Diagnosis is usually made by magnetic resonance imaging (MRI) which can visualize the structures of the brain, spinal cord, and the position of cerebellar tonsils relative to the foramen magnum.

Treatment

Treatment depends on the severity of the symptoms. Asymptomatic individuals usually require no treatment. Symptomatic cases are treated surgically, with a procedure known as a posterior fossa decompression, which creates more space for the cerebellum and relieves pressure on the spinal cord.

References

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• Meadows, J., Kraut, M., Guarnieri, M., Haroun, R. I., & Carson, B. S. (2000). Asymptomatic Chiari Type I malformations identified on magnetic resonance imaging. Journal of *Neurosurgery, 92(6), 920-926.
• Batzdorf, U. (1995). Chiari I malformation with syringomyelia. Evaluation of surgical therapy by magnetic resonance imaging. Journal of Neurosurgery, 82(5), 799-805.
• Noudel, R., Jovenin, N., Eap, C., Scherpereel, B., Pierot, L., Rousseaux, P., ... & Brotchi, J. (2008). Incidence of basilar invagination in Chiari malformation type I: comparative *morphometric study of 364 symptomatic patients with Chiari malformation type I. Journal of Neurosurgery: Spine, 9(5), 461-467.

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