C. Developmental disorders of the brainstem
- 1. Arnold-Chiari malformation includes displacement of the
cerebellar tonsils and fourth ventricle down into the cervical segments.
Other abnormalities of the brainstem in this malformation are less important.
See section III.
- 2. Agenesis
- a. inferior olivary nuclei may be absent for no known reason
- b. pyramids may be absent and this anomaly is often related
to abnormalities of the cerebral hemispheres