||Andrew G. Lee, MD, Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, TX; Professor of Ophthalmology, Weill Cornell Medicine; Mariam Hussain, Texas A&M College of Medicine Class of 2020
||We're going to talk today about the chiari malformation, used to be described as the 1-4 categories, but now we're pretty much only talking about chiari type I versus chiari type II. As you know, the chiari malformation is due to a volume problem between the posterior fossa and the cerebellum and the brainstem and so when you have too much stuff in a closed space, the tonsils can go down the foramen magnum. When the tonsils descend below the foramen magnum, we call that the chiari I malformation. If more stuff goes down the hole, parts of the brainstem, more severe Chiari II. Chiari II is often associated with myelomeningocele and other problems. The Chiari I can be either congenital or acquired. The way the Chiari malformation, both I and II, come to neuro-ophth is with nystagmus. The most common form of nystagmus we see with the Chiari malformation is downbeat nystagmus, but other forms of nystagmus can occur with the Chiari malformation. We can also see increased intracranial pressure from crowding at the foramen magnum and they can have hydrocephalus, or they might just have what looks like pseudotumor cerebri. There's no tumor, there's no mass, but they have novel edema, or they have signs of increased intracranial pressure or symptoms of increased intracranial pressure. We can also have esotropia, either from a six nerve palsy that is non localizing increased intracranial pressure related or patients sometimes present with acute comitant esotropia. Comitant just means it's the same in all directions, so as opposed to a six nerve palsy which is normally incomitant and worse towards the direction of the weak muscle, the lateral rectus at the sixth on the side that's affected. A comitant esotropia may be the presenting or only sign of the Chiari malformation. So we should be imaging for the Chiari malformation in neuro-ophthalmology in patients who have symptoms of increased intracranial pressure, headache, especially postural headache, and the usual symptoms of increased ICP, nausea, vomiting, pulse synchronous tinnitus, transient visual obscurations, or if they have signs of increased intracranial pressure, papilledema, six nerve palsy non localizing or down beat nystagmus or any form of nystagmus and a comitant acquired new onset esotropia. All of those require imaging, and the best imaging is the sagittal cut to look for the tonsillar descent at the level of the foramen magnum, and if there's more severe descent from the posterior fossa contents, that's called Chiari II.