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I'd like to begin now with a discussion

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of extra-axial collections.

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Extra-axial collections are generally categorized

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into epidural hematomas and subdural hematomas.

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I'd like to use this illustration to distinguish the two.

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This red collection

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is outside of the dura,

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marked in purple.

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As you can see,

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it is associated with a skull fracture,

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as well as an injury to the subjacent artery

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depicted in red.

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So this is an arterial bleed depicted in red.

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It's outside the dura,

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and therefore, this is what is termed an epidural hematoma.

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Epidural hematomas are generally caused by injury to the

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middle meningeal artery associated with temporal

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bone fractures. Alternatively,

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they occasionally will occur due to venous sinus injuries

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where the blood collects outside of the dura.

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Contrast that with this blue collection.

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This is a subdural

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hematoma. The subdural hematoma, as you can see,

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is below the dura,

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although still intracranially.

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And this is due to tearing of shearing

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veins that cross the subdural space.

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It is generally of a venous etiology as

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opposed to most of the epidurals,

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which are arterial with the exception of those

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that are associated with the venous sinus.

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So these are veins as opposed to the venous sinus.

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Let's talk a little bit more about the distinction between

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epidural hematomas and subdural hematomas.

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So, as I mentioned,

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epidural hematomas are associated

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with fractures in 90% of cases,

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and they are usually caused by tearing of either the

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dural venous sinus or the middle meningeal artery.

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They are biconvex in their shape,

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they're lenticular in shape,

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and they are confined by sutures, but not the dura.

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Epidural hematomas,

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despite the fact that they're arterial in their etiology,

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have a good prognosis. Subdural hematomas, however,

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are due to bridging vein tears.

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They usually occur over the convexities,

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and they are usually crescentic in their shape.

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So epidural is biconvex, subdural is crescentic.

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These have a worse prognosis than epidural hematomas.

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It doesn't make a lot of sense.

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It's kept me awake at night.

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Why is it that an epidural hematoma,

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which is arterial in its etiology

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and therefore higher pressure,

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would have a better prognosis than those

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patients who have subdural hematomas?

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And the answer to that is that most of the subdural

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hematomas are contracoup injuries, which means that

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it's been a significant back and forth injury.

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Whereas remember that epidural hematomas by virtue

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of being associated with the fracture,

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are usually at the coup and therefore detected relatively

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early and treated earlier and are not as much

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of a damage occurring to the brain.

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With respect to extra-axial collections,

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they usually do not contain hemosiderin as opposed to

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parenchymal hemorrhages, and they can evolve into lower

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density collections such that they look

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almost as low density as dirty CSF.

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And we will talk about things such as the ISO

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dense subdural hematoma and the hypodense.

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Chronic subdural hematoma and the subdural Hygroma.

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Subdural hygromas are theoretically pure CSF collections

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secondary to tearing of the meninges,

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as opposed to chronic subdural hematomas,

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which are a mixture of blood products and potentially CSF.

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I want to talk at this point about subdural hematomas.

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These are the indications for surgery as defined by the

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Humans and Win 7th edition for intervening

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for acute subdural hematomas.

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These include thickness greater than 10 mm or midline

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shift greater than 5 mm on CT, and this is generally

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measured at the level of the septum

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polysum as depicted previously.

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All patients who have acute subdural hematomas should

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undergo intracranial pressure monitoring with a

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pressure bolt or a ventriculostomy catheter.

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Another indication for surgery is a

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patient who's doing very poorly.

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So one who has a Glasgow Coma Scale less than nine,

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indicating moderate to severe head trauma,

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and one that may have a subdural hematoma that's

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less than 10 mm or less than 5 shift.

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So if it's not that large,

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but the patient is in extremis from the

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standpoint of their neurologic system,

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then they will intervene surgically.

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Here is a slide set of patients

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who have subdural hematomas.

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How do we know that this is a subdural hematoma?

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This is a crescentic collection, not biconvex,

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and therefore, it is a subdural hematoma.

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You notice that the patient has midline shift,

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which is probably around 1.5.

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Therefore, this patient is going to the OR.

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You notice that the thickness of this subdural hematoma,

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I would estimate it probably around 2 CM.

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That also is an indication for surgery.

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This collection crosses where we would normally

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expect to see the coronal suture,

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and therefore it's more likely to represent a subdural

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collection since epidural hematomas do not cross the bony

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sutures where the bone is attached to the dura.

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How about this patient on the right-hand side?

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This patient on the right-hand side?

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We see that the ventricles are shifted from right to left.

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We see subarachnoid space on the left side,

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but we have effacement of the subarachnoid

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space on the right side.

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The issue here is where is the cortical

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margin of the brain tissue?

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And you can actually see that the white matter

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here goes out about this far and then stops.

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And so the actual cortex of the brain

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is right along this direction.

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This patient has a collection known as an isodense

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collection. An isodense subdural hematoma.

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What do we mean by isodense?

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It is the same density as gray matter.

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So it is hard to detect is only by virtue of the

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displacement of the normal gray matter and the gray-white

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junction and the mass effect associated with the

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hemorrhage that one can identify this

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as an isodense subdural hematoma.

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A word about isodense subdural hematoma.

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Most of the time we say that isodense subdural hematomas

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are subdural hematomas that are one to two weeks old

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because they are not hyperdense of acute blood products.

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And therefore, as the time goes on, density,

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and this is time,

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the density goes down over the course of time.

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However, this assumes a normal hematocrit.

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If you have a patient who is anemic,

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their blood is not that dense as a person

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who has a normal hematocrit.

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So remember that the density of blood has to do with the

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hemoglobin molecule, not the iron of it, but the globin.

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But as the hemoglobin concentration increases,

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density increases. So if you have a patient who is anemic,

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for a variety of reasons,

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their density of their blood products goes down.

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This is particularly true, for example,

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at Johns Hopkins University where I work,

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because we have a large African American population.

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That has sickle cell disease or sickle cell

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anemia at a high rate.

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And these patients,

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because of their lower hematocrit,

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generally have the propensity for acute isodense

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subdural hematomas, not subacute ones.

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And this may also be true of those patients who

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are receiving chemotherapy, for example,

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where they become anemic or any other cause of anemia.

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So, to reiterate,

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generally an isodense subdural hematoma refers to one that

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is one to two weeks old on the way from initially being

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hyperdense, like you see in the image to the left,

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and then over the course of time,

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becoming hypodense as the blood products resolve.

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However,

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there are instances where you can have an acute isodense

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subdural hematoma related to the patient's hematocrit.