Final answer:
Chiari II malformation is typically present at birth and associated with other congenital conditions, while Chiari I malformation may present later in life and does not involve other congenital conditions.
Step-by-step explanation:
The Chiari II malformation and Chiari I malformation are two different conditions affecting the brain and spinal cord. Chiari II malformation is typically present at birth and is characterized by the downward displacement of the brainstem and cerebellum through the foramen magnum, which is the opening at the base of the skull. It is often associated with other congenital conditions, such as myelomeningocele, where the spinal cord protrudes through an opening in the vertebrae.
Chiari I malformation, on the other hand, is usually congenital as well but may not present symptoms until later in life. It involves the downward displacement of the cerebellar tonsils through the foramen magnum, without the involvement of other congenital conditions.
In summary, Chiari II malformation is typically present at birth and associated with other congenital conditions, while Chiari I malformation may present later in life and does not involve other congenital conditions.