Chiari malformation is a neurological condition in which brain tissue extends into the spinal canal. This abnormality occurs when part of the cerebellum—located at the back of the brain—pushes downward through the foramen magnum, the opening at the base of the skull. Chiari malformation can disrupt the normal flow of cerebrospinal fluid (CSF) and affect the brain and spinal cord, leading to a wide range of symptoms.

Types of Chiari Malformation

Chiari malformation is classified into several types based on severity and anatomical changes:

Type I

The most common form, often diagnosed in adolescence or adulthood. It involves the downward displacement of the cerebellar tonsils without involvement of the brainstem.

Type II (Arnold–Chiari Malformation)

Typically present at birth and associated with myelomeningocele, a form of spina bifida. Both the cerebellum and brainstem extend into the spinal canal.

Type III

A rare and severe form where parts of the cerebellum and brainstem protrude through an abnormal opening in the skull.

Type IV

Characterized by an underdeveloped or absent cerebellum. This type is extremely rare and often severe.