CHIARI MALFORMATION

Too much brain for your skull


Chiari Malformations occur when someone's skull isn’t big enough for their brain. This usually means that the posterior fossa of the skull is shrunken, which puts the squeeze on the cerebellum. So, the cerebellum is forced to poke its head into the spinal canal through the foramen magnum. The cerebellar tonsils are the most inferior part of the cerebellum, so they are usually the parts of the cerebellum to squeeze in there. 


Types?

Type 1 

The cerebellar tonsils herniate. Often asymptomatic, at least until adulthood. Hydrocephalus is rare, but it can cause syringomyelia (neck pain, cape-like analgesia, later on gets bilateral motor problems).


Type 2 

The cerebellar tonsils AND vermis herniate (2 structures). This is also called the Arnold-Chiari Malformation. Type 2 is much more severe. It will be really obvious during childhood. The damage to the vermis causes ataxia, vertigo and nystagmus. The CSF will be more blocked, and the hydrocephalus will be a lot more problematic (headache). The nearby medulla is often squished among the crowded posterior fossa (laryngeal stridor, tongue fasciculations, lower CN palsies, impaired reflexes). There is a decent chance that the patient will have another nasty disease as well, a myelomeningocele. Recall that it’s the most severe form of spina bifida where the spinal cord is squished into a bubble on the baby’s back. Syringomyelia is usually absent!



The cerebellum is being squished down the foramen magnum, which has several unfortunate consequences on neighboring structures. The 4th ventricle can be compressed, creating a non-communicating hydrocephalus. The medulla can be crushed, causing all sorts of nasty phenomena.