Chiari III malformation
Chiari III is one of the rarest of the Chiari malformations and is characterized by a high cervical or low occipital encephalocele and osseous defect with or without spinal cord involvement and may include many of the anatomical characteristics seen in the Chiari II malformation.
Type III is the most serious form of Chiari malformation (CM).
The cerebellum and brain stem protrude, or herniate, through the foramen magnum and into the spinal cord. Part of the brain’s fourth ventricle, a cavity that connects with the upper parts of the brain and circulates CSF, may also protrude through the hole and into the spinal cord.
In rare instances, the herniated cerebellar tissue can enter an occipital encephalocele, a pouch-like structure that protrudes out of the back of the head or the neck and contains brain matter. The covering of the brain or spinal cord can also protrude through an abnormal opening in the back or skull.
Type III causes severe neurological defects.
Out of 57 reported cases of Chiari III malformation, encephaloceles were in a high cervical/low occipital position in 23, 8 were in a high cervical position, 17 were in low occipital position, and the position in 9 cases was not reported. The pathogenesis of Chiari III malformation remains unclear. The majority of patients have concomitant hydrocephalus. Brain parts occurring in the sac from the most to least common include the following: cerebellum, occipital lobe, and parietal lobe. The severity of symptoms is correlated with the amount of brain structures within the encephalocele. Neurologic functional outcomes have been varied and depend on the neurological status of the patient before surgery 1).