| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (SA) Class of 2022, Baylor College of Medicine, Houston, Texas |
| Transcript |
So, today we're going be taking about shunt malfunction. It's really important that you know a little bit about shunts and shut malfunction because it can present to neuro-ophthalmology. The way it presents to us is the patient has a known shunt. So, for example, they've had a ventriculoperitoneal shunt for hydrocephalus or more commonly for idiopathic intracranial hypertension that has failed maximal medical therapy. Their chief complaint can either be on the afferent side (they have blurry vision, loss of vision or visual field), or on the efferent side (which is a sixth nerve palsy or the dorsal midbrain syndrome). So, both these complaints both an afferent and an efferent in a patient who has a shunt, you should be thinking about ventriculoperitoneal shunt malfunction, until proven otherwise. So, if we see papilledema and they didn't have it before well, that's easy they have increased intracranial pressure and the shunt isn't working. If we see a sixth nerve palsy, that is a non- localizing finding of increased intracranial pressure and can be either unilateral or bilateral. And because the shunt can decompress the ventricles if the ventricle gets big enough the aqueduct can enlarge and cause the dorsal membrane syndrome. So, the dorsal midbrain syndrome is also a sign and a symptom of a shut malfunction. So, these are the three things that we're going to be looking for. But what if the patient already has optic atrophy? Well then a dead nerve can't swell, and so if the patient has optic atrophy, we cannot utilize the papilledema as the marker of increased intracranial pressure. So, we're gonna have to still work this up. So, the workup for shunt malfunction is gonna be first to do a cat scan of the head non-contrast, and what we're looking for is ventriculomegaly. So, if the CT scan shows the half of the ventricles are getting bigger and bigger well of course the shunt isn't working. The problem is sometimes a shunt is not working but the ventricle is small, and that we call the slit ventricle. And in the slit ventricle the ventricle is collapsed and that could either be from too much drainage causing it to collapse. But it paradoxically can be in front of shunt malfunction because once the ventricle collapses the radius decreases, and as you know from the law of La Place that if the radius goes down to maintain the same tension, we have to have an increase in pressure. It's analogous to our alveoli we cannot allow our alveoli to collapse because if it does collapse the amount of pressure that's gonna be necessary to open back the alveoli in your lung is going to be too much. So we maintain that tension with surface tension, to maintain the wall tension to keep the alveoli from collapsing, and that is also an example of the Law of La Place. So, in the slit ventricle, the thing you need to know is a slit ventricle could represent shunt malfunction. If the CT scan doesn't show anything, we're gonna do a shunt series. A shunt series is just a bunch of x-rays going from the head all the way down to the abdomen. What we're looking for is a disconnection in the shunt. However, the shunt could be completely connected and still be broken because it's obstructed. And so, if the shunt series is negative we're gonna proceed to interrogate the shunt as well as do a lumbar puncture, and measure the pressure. We can inject technetium a radioactive isotope that's been liganded on to a biologic with a chelating agent called DTPA. Technetium-99 DTPA is one example of a radioisotope that we can inject directly into the reservoir of the ventriculoperitoneal shunt, and see how fast it takes, if at all, to get into the abdomen. So, if we see delay or no flow of the technetium radioactive isotope into the abdomen, we know that this shunt is either partially or fully obstructed. And that means we have to call the neurosurgery. But really you should be calling neurosurgery from the start in any patient who has a shunt in place, who has afferent or efferent complaints that suggest increased intracranial pressure. Or the reverse. Neurosurgery has already admitted the patient and are now calling us to look for papilledema, sixth-nerve palsy, or dorsal midbrain syndrome. But be especially worried when there's optic atrophy. And it really doesn't matter it CT and the shunt series are normal. We have clinical findings of shunt malfunction, it is broken. |
