| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (MH) Baylor College of Medicine, Houston, Texas |
| Transcript |
So today we're just going to talk a little bit about the pons, and as you know, the pons is in the middle of the brainstem. So we've got the midbrain, the pons which is this bulgy part, and the medulla. Usually neuro-oph we don't really go down to the medulla because the cranial nerves three and four are in the midbrain at the level of the superior and inferior colliculus, and it is six that's in the pons. So six has a nucleus in the caudal pons, then this fascicle piece, and it rises up that bone and you remember we talked about that bone before which is the clivus, and then turns at Dorello's canal, enters into the cavernous sinus through the superior orbital fissure to the orbit. So today we're just going to be talking about this piece right here of the sixth, and that's because the pontine syndromes can affect both the sixth nerve nucleus and the sixth nerve fascicle as well as the interneuron between the sixth nerve nucleus and the third nerve which is the medial longitudinal fasciculus. So, when we have pontine lesions, we can either be dealing with ventral lesions or dorsal lesions. You're very familiar with the dorsal midbrain syndrome, but these are dorsal pontine syndromes. The dorsal pontine syndromes can either affect the dorsal structures which is like the sixth nerve nucleus, and so if you ding out the sixth nerve nucleus dorsally, you'll get a horizontal gaze palsy. If you ding out the MLF you'll get an internuclear ophthalmoplegia. You can have combinations of these things. A horizontal gaze palsy which is a one plus an INO which is a half, which is a one and a half gaze palsy. And because the seventh nerve kind of wraps around the sixth nerve nucleus, we can get seventh nerve dysfunction and that seven plus one and a half would be like an eight and a half. So these dorsal things often produce seventh nerve lesions. So, the dorsal pontine syndromes come to neuro-ophthalmology primarily because the dorsal syndromes have eye problems (horizontal gaze palsy, sixth nerve fascicle what causes sixth nerve palsy, INO MLF with or without seventh). However, you need to know a little bit about the ventral pontine syndromes as well because the ventral ones are more dangerous because they have other things involved. And so if you have a medial ventral syndrome, you might just get the sixth plus the corticospinal tract which is going to cause hemiparesis. So, the combination of a right hemiparesis and a left sixth nerve palsy is going to be that left ventral pons, and if it's sufficiently medial it'll miss this seven. However, if the lesion goes a little bit laterally, it'll get both six and seven and corticospinal tract, and so by adding in that seven laterally that's also a ventral problem but because it's lateral you got a six, a seven, and a hemiparesis. This we call Millard Gubler. If we just have the medial but we miss the seven, similar hemiparesis; a sixth on one side and a contralateral hemiparesis. That we call Raymond. And if it's more caudal it'll involve the lower brainstem cranial nerves and so you might get a seven, an eight, a Horner's syndrome, a five, a six. This is called Foville. So Foville just has a lot more stuff because it's more extensive either rostral caudally or more medial lateral. It's just bigger. So the Foville has way more stuff. The dorsal pontine syndromes are easy. They come to us with ophthalmoplegia, horizontal gaze palsy, fascicular sixth, INO one and a half with or without the seventh as the genu. The ventral pontine lesions a little more difficult; however, you're going to be involving other structures. Leminiscus which means they might have difficulty with hemi-sensory loss and ataxia from the cerebellar afferent and efferent. And the ones that affect us, Millard Gubler (six and seven plus corticospinal tract),Raymond (corticospinal tract plus hemiparesis on the contralateral side), Foville (involving your face, both sensation in the face, facial nerve seven, Horner's syndrome, eight nerve dysfunction, more caudal extension. Foville involving way more stuff). These three are the ventral pontine centers that come to us. There are other pontine syndromes like getting locked in or having pure sensory versions of this which go to neurology. The ones that come to us are the dorsal pontine syndromes that involve the nucleus or the fascicle or the MLF. The ventral ones when they involve six. We really don't see the way lateral ones because those don't come to us. We only see the ones that have the double vision, and that means the ones that knock out either the MLF or the sixth nerve fascicle or its nucleus. So you need to know a little bit about the dorsal pons. |
