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Overview of Brain Herniation Types

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As I mentioned,

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the secondary complications of traumatic brain injury are

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more likely to cause permanent damage

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than those of the primary injury.

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So far, we've looked at some of the vascular complications,

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secondary complications of traumatic brain injury,

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demonstrating dissections, occluded vessels,

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as well as pseudo aneurysms,

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with the potential for embolic infarcts,

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secondary to the pseudo aneurysm.

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Now, I'd like to talk to you a little bit about herniations.

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Again,

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this is usually not what is occurring at the initial time of

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the insult with the traumatic event is usually something

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that we see over the course of time with

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delay after the initial event.

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The different types of hernia depend upon where the

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patient's lesion is and these lesions that I refer to may

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be interparenchymal. That is a hematoma or contusion.

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Or they may be extra-axial.

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That is a subdural hematoma or an epidural hematoma.

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Both of them can cause enough mass effect that leads to

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herniation. Now, when we refer to the right left shift,

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that can occur with an extra-axial collection.

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In this case, an isodense subdural hematoma,

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we usually refer to the degree of displacement

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from the midline of the septum pellucidum.

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However,

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simple displacement from the midline does not necessarily

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lead to or qualify for subfalcine herniation.

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By subfalcine herniation,

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we mean that the patient has brain tissue which

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is crossing over from, in this case,

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the right side to the left side under the falx cerebri.

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And this is the free edge of the falx cerebri.

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So why?

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While normally we can have a degree of midline shift without

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brain tissue herniating over when we see the brain tissue

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actually crossing from right to left, in this instance,

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that's where we refer to the term subfalcine herniation.

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So although midline shift is concurrent

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with subfalcine herniation,

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it does not complete the qualifications

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for subfalcine herniation.

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Subfalcine herniation is usually due to mass

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effect in the superior portion of the brain,

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not the inferior portion of the brain,

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and in the supratentorial portion of the brain,

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certainly not the infratentorial posterior fossa

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of the brain. In a similar fashion,

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we have a degree of uncal herniation.

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By uncal herniation,

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we mean that the medial temporal lobe

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extends into the cistern and will.

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Will lead to effacement of the cisterns

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around the brain stem.

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So that would be uncal herniation when that uncus or when

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the amygdala or when the medial temporal lobe

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then crosses downward the tentorial edge.

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And you see brain tissue below the tentorial edge,

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for example, in a coronal image,

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then we would say that the patient had transtentorial uncal

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herniation or transtentorial temporal lobe herniation

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or transtentorial herniation. So again,

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this is a degree midline shift to subfalcine

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herniation uncal deviation,

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uncal herniation to transtentorial herniation as it goes

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downward. These are, again, supratentorial herniations.

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When we refer to cerebellar herniations,

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we're obviously talking about the posterior fossa.

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And again, this may be both an intraparenchymal.

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Hemorrhage or it may be extra-axial as in an

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epidural hematoma or a subdural hematoma.

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So again,

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posterior fossa for upward and downward

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cerebellar herniation.

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A lesion in the central aspect of the cerebellum may lead

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to this cerebellar tissue herniating upwards through the

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tentorial incisura the opening of the tentorium superiorly

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in that place it will compress the midbrain and efface

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the perimesencephalic cisterns. At the same time,

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1 may have downward cerebellar herniation what

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we usually refer to as tonsillar herniation.

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And that's when the tonsils are seen at the foramen magnum

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herniating downward through the foramen magnum.

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This then causes compression on the cervical medullary

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junction and the medulla and can lead

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to cardiorespiratory arrest.

Report

Description

Faculty

David M Yousem, MD, MBA

Professor of Radiology, Vice Chairman and Associate Dean

Johns Hopkins University

Tags

Trauma

Spine

Skull Base

Non-infectious Inflammatory

Neuroradiology

Emergency

CT

Brain

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