| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (AC) Class of 2023, Baylor College of Medicine, Houston, Texas |
| Transcript |
So today we're going to be talking about spontaneous intracranial hypotension and that's different than idiopathic intracranial hypertension, so we have SIH versus IIH. One is too high an intracranial pressure and the other is too low an intracranial pressure. Now it doesn't have to be spontaneous, it could be post-surgical or post-traumatic, but the ones that normally come to us don't have a cause and so they are spontaneous intracranial hypertension. And so the hypotension could actually be result of hypertension. So if you have IIH and high enough pressure and an empty sella it can erode through the floor to sella and cause a CSF rhinorrhea or CSF otorrhea and when the high pressure is released, created by the dehiscence, you suddenly have spontaneous intracranial hypotension now, even though the cause was actually hypertension. We can differentiate these both clinically and radiographically, and so the things that come to us in neuro-ophth clinically from intracranial hypotension or intracranial hypertension are non-localizing sixth nerve palsy and it's non-localizing because you can't tell where the lesion is. In fact, there is no lesion, it's just pressure. As you know, the sixth nerve leaves the pons and its root exit zone at the pons, it climbs up this bone, the clivus, and then turns 90 degrees at the petroclival ligament. And so because it's tethered right here and right here, the subarachnoid space can affect that sixth nerve. So either low pressure can make stretch or high pressure can make stretch of the sixth nerve right in this subarachnoid space as it's climbing this clivus. And so double vision by knocking a horizontal diplopia with an incomitant esotropia and an abduction deficit, either unilateral or bilateral, could be a non-localizing finding of both increased intracranial pressure and decreased intracranial pressure from the sixth nerve palsy. In addition, if it's high pressure, normally we have papilledema. And so that is a differentiating feature because intracranial hypotension does not produce papilledema. However, if the nerve is already atrophic or if the nerve is normal, it doesn't differentiate between the two. And finally you might have symptoms of the dorsal midbrain syndrome and it's the same mechanism except you're at the level of the midbrain this time. So at the level of the midbrain, the dorsal midbrain, you might have lid traction, the Collier's lid retraction sign, or an upgaze palsy or the sunsetting sign where the eyes are looking down like near dissociation of the pupils and convergence retraction nystagmus. So patients who have a shunt could have signs of increased intracranial pressure from shunt malfunction and present us the dorsal midbrain syndrome. So the key clinical features are non-localizing sixth nerve palsy, the dorsal midbrain syndrome, and if it's increased intracranial pressure, papilledema. Radiographically, we're gonna be able to tell the difference as well. So on the MRI scan, from increased intracranial pressure, idiopathic intracranial hypertension, we have fluid in the sheet, flattening of the globe, empty sella and stenosis of the venous sinuses. When you have intracranial hypotension, instead of an empty sella you have a full sella because of venous congestion. We do not see the venous sinus stenosis but instead we see meningeal enhancement because the venous congestion. And so we get a full rather an empty sella and venous congestion with dural enhancement rather than venous sinus stenosis in intracranial hypertension. And clinically, the symptoms are sometimes the same. They both have headache but in low pressure headaches, the patient's headache is worse when they stand up versus high pressure headaches it's worse when they lie down. They can have the diplopia from the non-localizing sixth nerve palsy. They could have pulse-synchronous tinnitus, which is usually from increased intracranial pressure from venous sinus stenosis. And the patients might have loss of vision from papilledema, so the intracranial hypotension people normally don't have vision loss because they don't have the papilledema. If however, you see vision loss, optic atrophy, or papilledema, it could still be increased intracranial pressure that led to low intracranial pressure. If the high intracranial pressure erodes through the sella and causes a CSF leak so it kind of treats it and if you treat someone who has intracranial hypotension and the leak is found and you've closed that leak either surgically or the blood patch, they might get intracranial hypertension. And so SIH could be fixed and become IIH. So in summary you should know the difference between SIH, spontaneous intracranial hypotension, and intracranial hypertension -that's IIH versus SIH. The radiographic features: sixth nerve palsy, papilledema, dorsal midbrain syndrome. You should know the differentiating radiographic features of both conditions and that one can lead to the other. |
