| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (AC) Baylor College of Medicine, Houston, Texas |
| Transcript |
Today we're going to be talking about posterior fossa cysts, cystic lesions, and the reason this comes to neuro-ophth is sometimes these patients have hydrocephalus, they have to be shunted and sometimes you have to shunt the cyst, which is a cysto-peritoneal shunt versus a ventriculo-peritoneal shunt and so what that means for us in neuro-ophth is we could have papilledema, the disc non-localizing finding of increased intracranial pressure. If we have involvement of the aqueduct you can have the dorsal midbrain syndrome,where the hydrocephalus itself is acting as the mass lesion pressing on the dorsal midbrain. And we can have a non-localizing number-6 palsy from increased intracranial pressure so these are the ways that these cystic lesions in the posterior fossa come to me. And usually neurosurgery is asking us areal simple question: do we see evidence of increased intracranial pressure. And the reason is sometimes it's difficult to differentiate these posterior fossa cystic lesions. And so one of the prototypes that you're aware of is if you have vermian abnormalities - so you have vermian hyperplasia or a plasiaraised rarely. So if you have too small of a vermis aplasia or hyperplasia of the vermis, that can lead to this whole thing moving up. And in that setting, they don't have a very good vermis here, the big malformation back here. So this posterior malformation created by the vermi and atrophy causing a fourth ventricle that is quite dilated,that thing is called the Dandy Walker malformation. And so the Dandy Walker is characterized by inferior vermian hypoplasia and is a really dilated fourth ventricle. So that's one malformation that you need to know about and that can come to us. Usually that's a childhood thing, but it can occur later. And you can have problems from the lack of fenestration of the Foramen of Magendie, so if you have Magendie Foramen here and it doesn't do its job, it's not fenestrated, then you'll get a big cyst right here, and that thing is called the Blake's pouch cyst. Blake's pouch cyst. It's also a malformation presumably because you have something wrong with the foramen not fenestrating. And then we've got the one that most commonly comes to me which is a reduplication of the arachnoid, and that thing is called an arachnoid cyst. And so that thing could have increased intracranial pressure, mass effect. It's a reduplication arachnoid cyst. And then you have the one that we don't do anything with, which is the mega cisterna magna. That's just a big thing that was already big. It was Cisterna Magna but it's bigger,so that's a normal variant. So if we have just a big mega Cisterna Magna, we don't we don't really operate on. That's an incidental finding, that's something that people see on scans, and we don't even rescan that. So mega cisterna Magna is not going to be coming to me because it doesn't have any findings, it's just an incidental. The ones that come to me are the arachnoid cyst because it has mass effect,that's what we're looking for this, and so they might put a shunt right here. Alternatively, they might fenestrate this cyst. So when you have a posterior fossa cystic lesion in neuro-ophth, it's really not that important that you know which one it is. Don't operate pretty much on the mega Cisterna Magna, that's normal variant. If it's arachnoid cyst what we're interested in is, is there mass effect, shift, papilledema, dorsal midbrain syndrome, 6th nerve palsy, Dandy Walker malformation - that does have neuro-ophth findings but usually that's a kid thing, and the Blake's pouch - this can be differentiated because there's lack of fenestration in the Foramen of Magendie but that the vermian atrophy is absent. |
