| Transcript |
"So today, we're going to be talking about what you need to know as an ophthalmologist in the bottom part of the brainstem, which is the medulla. And the predominant thing in the medulla that we need to know about are lateral lesions. And if you have a lateral medullary syndrome, the most common cause of that is the Wallenberg. So the Wallenberg syndrome is usually an infarction from the PICA, the posterior inferior cerebellar artery. PICA, it produces a lateral medullary syndrome, and that thing has an eponym called the, "Wallenberg syndrome". And so they're going to have a lateral involvement, which is going to involve the oculosympathetic pathway and produce the Horner's syndrome, which is going to make the anisocoria. And because of the damage to the vestibular system, a central vestibulopathy might occur which might produce a rotary nystagmus. But it can be other forms of nystagmus as well, that are central vestibulopathy. And the key and differentiating feature of the Wallenberg is the crossed sign, so they have a face problem on one side, and the body on the other side. So this is a crossed sign, so the trigeminal to the face is usually an ipsilateral problem, but because of the involvement at the level of the brainstem, the patient's body findings; temperature and pain are on the contralateral side, so this is what we call a crossed sign. And then the patients might have diplopia from a skewed deviation. So in the medulla, because the third, fourth and sixth nerve do not go down to the medulla, the third and fourth are at the level of the midbrain and the sixth is at the level of pons, normally we don't see double vision. And we never hardly ever go down to the medulla land, however, you should know that we do sometimes have to be wary of medullary syndromes both because the sympathetic pathway descends into the medulla, but also you can get skewed deviation causing diplopia from a medullary lesion. The other thing that you need to know about for the medulla for neurop is the Guillain Mollaret triangle. In the Guillain Mollaret triangle, we have any lesion that can extend from the red nucleus in the midbrain all the way to the dentate nucleus into the cerebellum, and down to the medulla, which is called the inferior olive. So, this triangle, the Guillain Mollaret triangle, any lesion that occurs within this triangle from the red nucleus, to the inferior olive, or the dentate on this contralateral side of the cerebellum, can result in a very specific eye finding called, "oculopalatal myoclonus". And what this means is, the eye is moving in a small, pendular, vertical movement. It's not downbeat nystagmus or upbeat nystagmus, it's this pendular vertical. And you need to look in their mouth for the palate. The palate could be synchronous or asynchronous movement in oculopalatal myoclonus, and you have a disruption basically in the inhibitory input somewhere inside the Guillain Mollaret triangle. So it's usually a delayed effect, often from a pontine lesion, like a pontine hemorrhage or a cavernous malformation, and that releases the inhibition on the inferior olive and that causes inferior olivary hypertrophy on the MRI scan. So the olive starts getting bigger. And because the medulla also provides the support for the lower cranial nerves to your palate, the palate will jump. So if we disinhibit the palate, it'll start moving like this. And because we have a lesion in the Guillain Mollaret triangle, it's also disinhibiting the eye movement. So we'll have bilateral, conjugate, slow, pendular, small amplitude vertical movement. Oculopalatal myoclonus. So every patient who has a vertical bilateral conjugate movement that isn't downbeat or upbeat, we should look in their mouth. And what you're looking for is oculopalatal myoclonus, it is a lesion in the Guillain Mollaret triangle. It causes MRI finding of inferior olivary hypertrophy, and is one of the two things you need to know about the medulla." |
