| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (NK) Baylor College of Medicine, Houston, Texas |
| Transcript |
"So, today I want to tell you about two interesting things which is the Duret Hemorrhage and the Kernohan's Notch Phenomenon. The reason these are important syndromes to know about is because they can be supratentorial in origin, either iatrogenic or traumatic and that means they could be a post-neurosurgical case, and they present with oculomotor findings. So when we have ocular motor findings of cranial nerves three, four and six - normally that implies that there's a brainstem problem. However, there are localizing and non-localizing as well as false localizing ocular motor signs, and the prototypes for learning about these things are the Duret Hemorrhage and Kernohan's Notch Phenomenon.; So if you have a lesion in your brain and let's just say it's in the frontal lobe, normally the symptoms and the signs are going to be confined to that location in the frontal lobe. However, if you have transtentorial herniation, you can get compression of the brainstem. So even though the problem is way up here in the cortex, when there's mass effect and shift, the cranial nerves can be affected either from a hemorrhage in the brainstem - for example, if the herniation presses on the blood vessels, the perforating blood vessels from the basilar into the pons, you can get a pontine hemorrhage even though your problem was in the right frontal lobe, you might get a left six in the pons from a Duret Hemorrhage. So, a Duret Hemorrhage is an infratentorial bleed from a supratentorial lesion causing transtentorial herniation and compression of the blood vessels that leads to the hemorrhage. And so, those pontine signs from the oculomotor signs are horizontal problems - six nerve palsy, unilateral or bilateral intranuclear ophthalmoplegia would be adduction deficit rather than an abduction deficit or any combination of those things. Horizontal gaze palsy, which have different names and you can watch the videos for that. One and a half syndrome, WEB INO (the Wall-Eyed Bilateral INO), or unilateral INO. So those are localizing signs because the Duret Hemorrhage is an infratentorial hemorrhage even though the problem was supratentorial. So when we're confronted with ocular motor findings from supratentorial, it could be a real localizing hemorrhage in the pons or the midbrain called a Duret. ; The alternative is the transtentorial herniation occurs and this is the tentorium and when that happens the third nerve can get compressed. So the tentorium is rigid dura, so even though the lesion is frontal when the transtentorial herniation occurs, it could tilt the tentorium like this and the nerve on the contralateral side can get trapped and compressed producing a third nerve palsy. And so even the lesion might be on the left side, it might produce a right third. So, you'll think the lesion is in the right side when it really is on the left side. You'll think the lesion is in the infratentorial third nerve pathway midbrain, fascicles, subarachnoid space when in reality the lesion is a supratentorial hemorrhage or a supratentorial mass. And that Kernohan Notch Phenomenon is that compression from the transtentorial herniation and that is a false localizing sign. It tells you not only the wrong location, it might be the wrong side. So it's falsely localizing and falsely lateralizing. ; And then finally if you have a hemorrhage or a lesion that's large enough in your brain, you can get a sixth nerve palsy and that can just be from increased intracranial pressure. As you know the sixth nerve exits the pons, goes up the clivus and then turns 90 degrees to enter into the cavernous sinus, but it's tethered at those two locations. The root exit zone in the pons and at the petroclival ligament in Dorello's Canal. So because it's tethered at those two locations, elevation of intracranial pressure or a decrease in intracranial pressure - intracranial hypertension or intracranial hypotension - will stretch the cranial nerve six in that location and that is a non-localizing sign of intracranial pressure. Either too high or too low. So you should know about the Duret Hemorrhage, a hemorrhage in your brainstem from perforators from the basilar in the infratentorial fossa from something that's going on in the supratentorial region whether that's trauma, a hemorrhage or neurosurgery. And the Kernohan's Notch Phenomenon, compression of the third from transtentorial herniation that is a false localizing sign because it's telling you not only the wrong side, [but also] the wrong location. The lesion is actually supratentorial. Or a non-localizing finding that's usually non-localizing six nerve from both intracranial hypertension or intracranial hypotension. Duret and Kernohan." Summary: • Ocular motor findings can be iatrogenic or traumatic (post-neurosurgical) • When there are issues with CN III, IV and VI brainstem problem o Can be localizing, non-localizing or falsely localizing ocular motor signs o Prototypes for these signs are Duret Hemorrhage and Kernohan's Notch Phenomenon • Three Possibilities to Ocular Motor Findings in the Brainstem o Duret Hemorrhage - brainstem hemorrhage caused by supratentorial issue affecting the infratentorial fossa. Localizing signs o Kernohan's Notch Phenomenon - supratentorial lesion causing compression of CN III from transtentorial herniation. Falsely localizing and falsely lateralizing o Non-localizing CN VI issue - due to either intracranial hypertension or hypotension • Duret Hemorrhage; o; Normally, the signs and symptoms of a lesion are confined to the location of the initial bleed o In Duret's, there is mass effect and shift Ex: a right frontal lobe problem can cause compression of the perforating blood vessels from the basilar into the pons pontine hemorrhage CN VI issues on the left o Definition: an infratentorial bleed from a supratentorial lesion causing transtentorial herniation and compression hemorrhage in the pons or midbrain; o; Presents with Horizontal Problems (Localizing Signs) CN VI Palsy Unilateral or Bilateral INO One and a Half Syndrome Wall-Eyed Bilateral INO (WEB INO) • Kernohan's Notch Phenomenon o Definition: Supratentorial lesion causing transtentorial herniation compressing CN III; o; Presents as a CN III palsy on the contralateral side to the lesion Ex: Lesion on left side produces palsy on right sided CN III; o; Falsely localizing and falsely lateralizing • Non-Localizing o Hemorrhage or lesion that is so large that is causes a CN VI palsy from increased intracranial pressure o Anatomy CN VI exits pons up clivus turns 90 degrees enters cavernous sinus CN VI tethered at 1) root exit zone in pons and 2) petroclival ligament in Dorello's Canal Because CN VI is tethered, changes in intracranial pressure (hyper or hypotension) stretch CN VI (non-localizing sign of intracranial pressure) |
